Radiological Anatomy - Faculty of Applied Health Sciences Technology 2020 Final Exam PDF

Radiological Anatomy FACULTY OF APPLIED HEALTH SCIENCES TECHNOLOGY Prepared by: Assistant Professor Dr. Sahar Mahmoud Abd elsalam Revised By Professor Ahmed Hesham Saeed Radiological Anatomy Faculty of Applied Health Sciences Technology Table of content Section number Items Page number 1 Head and neck 2 2 Neuroanatomy 26 3 Chest 32 4 Gastrointestinal tract 49 5 Genitourinary system 85 6 Musculoskeletal 107 1 Radiological Anatomy Faculty of Applied Health Sciences Technology Section 1: Head and neck THE SKULL AND FACIAL BONES The skull consists of the calvarium, facial bones and mandible. The calvarium is the brain case and comprises the skull vault and skull base. The bones of the calvarium and face are joined at immovable fibrous joints, except for the temporomandibular joint, which is a movable cartilaginous joint. The skull vault: The skull vault is made up of several flat bones, joined at sutures, which can be recognized on skull radiographs. The bones consist of the diploic space - a cancellous layer containing vascular spaces - sandwiched between the inner and outer tables of cortical bone. The skull is covered by periosteum, which is continuous with the fibrous tissue in the sutures. The periosteum is called the pericranium externally and on the deep surface of the skull is called endosteum. The endosteum is the outer layer of the dura. The diploic veins within the skull are large, valveless vessels with thin walls. They communicate with the meningeal veins, the dural sinuses and the scalp veins. The paired parietal bones form much of the side and the roof of the skull and are joined in the midline at the sagittal suture. Parietal foramina are paired foramina or areas of thin bone close to the midline in the parietal bones. They are often visible on a radiograph, may be big and may even be palpable. They may transmit emissary veins from the sagittal sinus. The frontal bone forms the front of the skull vault. It is formed by two frontal bones that unite at the metopic suture. The frontal bones join the 2 Radiological Anatomy Faculty of Applied Health Sciences Technology parietal bones at the coronal suture. The junction of coronal and sagittal sutures is known as the bregma. The occipital bone forms the back of the skull vault and is joined to the parietal bones at the lambdoid suture. The lambdoid and sagittal sutures join at a point known as the lambda. The greater wing of sphenoid and the squamous part of the temporal bone form the side of the skull vault below the frontal and parietal bones. The sutures formed here are: (i) the sphenosquamosal suture between the sphenoid and temporal bones; (ii) the sphenofrontal and sphenoparietal sutures between greater wing of sphenoid and frontal and parietal bones; and (iii) the squamosal suture between temporal and parietal bones. The sphenofrontal, sphenoparietal and squamosal sutures form a continuous curved line on the lateral skull radiograph. The Skull base: The inner aspect of the skull base is made up of the following bones from anterior to posterior: The orbital plates of the frontal bone, with the cribriform plate of the ethmoid bone and crista galli in the midline; The sphenoid bone with its lesser wings anteriorly, the greater wings posteriorly, and body with the elevated sella turcica in the midline; Part of the squamous temporal bone and the petrous temporal bone; and The occipital bone. 3 Radiological Anatomy Faculty of Applied Health Sciences Technology Individual bones of the skull base The orbital plates of the frontal bones are thin and irregular and separate the anterior cranial fossa from the orbital cavity. The cribriform plate of the ethmoid bone is a thin, depressed bone separating the anterior cranial fossa from the nasal cavity. It has a superior perpendicular projection, the crista galli. The sphenoid bone consists of a body and greater and lesser wings, which curve laterally from the body. The body houses the sphenoid sinuses and is grooved laterally by the carotid sulcus, in which the cavernous sinus and carotid artery run. The sphenoid body has a deep fossa superiorly known as the sella turcica or pituitary fossa, which houses the pituitary gland. On the anterior part of the sella is a prominence known as the tuberculum sellae; anterior to this is a groove called the sulcus chiasmaticus, which leads to the optic canal on each side. The optic chiasm lies over this sulcus. Two bony projections on either side of the front of the sella are called the anterior clinoid processes. The posterior part of the sella is called the dorsum sellae, and this is continuous posteriorly with the clivus. Two posterior projections of the dorsum sellae form the posterior clinoid processes. The temporal bone consists of four parts: A flat squamous part. A pyramidal petrous part. An aerated mastoid part; and An inferior projection known as the styloid process. 4 Radiological Anatomy Faculty of Applied Health Sciences Technology The zygomatic process projects from the outer side of the squamous temporal bone and is continuous with the zygomatic arch. The curved occipital bone forms part of the skull vault and posterior part of the skull base. It has the foramen magnum in the midline, through which the cranial cavity is continuous with the spinal canal. Cranial fossae : The anterior cranial fossa is limited posteriorly by the sphenoid ridge and anterior clinoid processes and supports the frontal lobes of the brain. The middle cranial fossa is limited anteriorly by the sphenoid ridge and anterior clinoid processes. Its posterior boundary is formed laterally by the petrous ridges and in the midline by the posterior clinoid processes and dorsum sellae. It contains the temporal lobes of the brain, the pituitary gland, and most of the foramina of the skull base. The posterior cranial fossa is the largest and deepest fossa. Anteriorly it is limited by the dorsum sellae and the petrous ridge, and it is demarcated posteriorly on the skull radiograph by the groove for the transverse sinus. It contains the cerebellum posteriorly, and anteriorly the pons and medulla lie on the clivus and are continuous, through the foramen magnum, with the spinal cord. Radiological features of the skull base and vault Plain films Several projections are required for a full assessment of the skull vault. The standard projections are lateral, OF20 and Towne's projections. The pituitary fossa is visible on OF20 (occipitofrontal view with 20° caudal angulation), FO30 (fronto-occipital projection with 30° caudal 5 Radiological Anatomy Faculty of Applied Health Sciences Technology angulation) and SMV views, but the lateral view is the most frequently used for its assessment. The major sutures have been described. The metopic suture between the two halves of the frontal bone normally disappears by 2 years of age, but persists into adulthood in approximately 10% of people, and may be incomplete. The spheno-occipital synchondrosis is the suture between the anterior part of the occipital bone and the sphenoid body. This usually fuses at puberty. Intraoccipital or mendosal sutures are often seen extending from the lambdoid suture and should not be mistaken for fractures. Wormian bones are small bony islands that may be seen in suture lines and at sutural junctions, particularly in relation to the lambdoid suture. Cross-sectional imaging Computed tomography (CT) provides excellent visualization of the skull base and foramina when narrow high resolution images are obtained. MRI with narrow section thickness slices is excellent for demonstration of the soft tissue contents of the foramina, in particular the cranial nerves. The plane of imaging can be chosen to demonstrate the structure of interest: for example, imaging in several planes is necessary to demonstrate the course of the facial nerve through the skull base from its entry into the internal auditory canal to its exit through the stylomastoid foramen. The posterior fontanelle closes by 6-8 months of age and the anterior fontanelle is usually closed by 15-18 months. Two pairs of lateral fontanelles close in the second or third month. By 6 months the sutures have narrowed to 3 mm or less. 6 Radiological Anatomy Faculty of Applied Health Sciences Technology The facial bones : Several bones contribute to the bony skeleton of the face, including the mandible, which forms the only freely mobile joint of the skull. The maxillae, zygomata and mandible contribute most to the shape of the face, and the orbits, nose and paranasal sinuses form bony cavities contained by the facial skeleton. The zygoma This forms the eminence of the cheek and is also known the malar bone. It is a thin bony bar that articulates with the frontal, maxillary and temporal bones at the zygomaticofrontal, zygomaticomaxillary and zygomaticotemporal sutures. Its anterior end reinforces the lateral and inferior margins of the orbital rim. The zygoma forms the lateral boundary of the temporal fossa above and the infratemporal fossa below. The nasal bones The paired nasal bones are attached to each other and to the nasal spine of the frontal bone. The bony orbit: The orbit is a four-sided pyramidal bony cavity whose skeleton is contributed to by several bones of the skull. The base of the pyramid is open and points anteriorly to form the orbital rim. Lateral, superior, medial and inferior walls converge posteromedially to an apex, on to which the optic foramen opens, transmitting the optic nerve and ophthalmic artery from the optic canal. The lateral orbital wall is strong 7 Radiological Anatomy Faculty of Applied Health Sciences Technology and is formed by the zygomatic bone in front and the greater wing of sphenoid behind. It separates the orbital cavity from the temporal fossa. The superior wall, or roof, is thin and undulating and separates the orbit from the anterior cranial fossa. It is formed by the orbital plate of the frontal bone in front and the lesser wing of sphenoid behind. The medial orbital wall is a thin bone contributed to by maxillary, lacrimal and ethmoid bones, with a small contribution from the sphenoid bone at the apex. It separates the orbit from the nasal cavity, ethmoid air cells and anterior part of sphenoid. The bone between the orbit and ethmoids is paper-thin and is known as the lamina papyracea. The inferior wall, or floor, is formed by the orbital process of the maxillary bone, separating the orbit from the cavity of the maxillary sinus. The orbital process of the maxillary bone also extends superomedially to contribute to the medial part of the orbital rim, and the zygoma contributes to the orbital floor laterally. The superior orbital fissure is a triangular slit between the greater and lesser wings of sphenoid (converging lateral and superior walls of the pyramid). The inferior orbital fissure is a slit between the lateral and inferior walls of the orbit as they converge on the apex. Radiology of the bony orbit Plain films The orbits may be assessed on OF20 and OM projections. The floor of the orbit and the infraorbital canal are best seen on the OM and OM30 projections. Computed tomography 8 Radiological Anatomy Faculty of Applied Health Sciences Technology The bony orbit and its soft-tissue contents are demonstrated very well by CT. Axial or coronal images may be obtained. Coronal imaging shows the floor of the orbit and is useful for the assessment of trauma where a fracture is suspected. MRI is more valuable for demonstration of the soft- tissue contents of the orbit than the bone. THE NASAL CAVITY AND PARANASAL SINUSES The nasal cavity is a passage from the external nose anteriorly to the nasopharynx posteriorly. The frontal, ethmoid, sphenoid and maxillary sinuses form the paired paranasal sinuses and are situated around, and drain into, the nasal cavity. The entire complex is lined by mucus secreting epithelium. The nasal cavity This is divided in two by the nasal septum in the sagittal plane. The nasal septum is part bony and part cartilaginous. The floor of the nasal cavity is the roof of the oral cavity and is formed by the palatine process of the maxilla, with the palatine bone posteriorly. The lateral walls of the cavity are formed by contributions from the maxillary, palatine, lacrimal and ethmoid bones. These walls bear three curved extensions known as turbinates or conchae, which divide the cavity into inferior, middle and superior meati, each lying beneath the turbinate of the corresponding name. The space above the superior turbinate is the sphenoethmoidal recess. Blood supply of the nasal cavity 9 Radiological Anatomy Faculty of Applied Health Sciences Technology -The sphenopalatine artery is the terminal part of the maxillary artery. -The greater palatine artery. -The superior labial branch of the facial artery. -Anterior and posterior ethmoidal branches of the ophthalmic artery from the internal carotid artery. The paranasal sinuses The frontal sinuses These lie between the inner and outer tables of the frontal bone above the nose and medial part of the orbits; they vary greatly in size and are often asymmetrical. They may extend into the orbital plate of the frontal bone. The ethmoid sinuses These consist of a labyrinth of bony cavities or cells situated between the medial walls of the orbit and the lateral walls of the upper nasal cavity. The sphenoid sinuses These paired cavities in the body of the sphenoid are often incompletely separated from each other, or may be subdivided further into smaller bony cells. The maxillary sinuses The maxillary sinuses, or antra, are the largest of the paranasal sinuses. They are sometimes described as having a body and four processes. The processes comprise: (i) the orbital process, which extends superomedially to contribute to the medial rim of the orbit; (ii) the zygomatic process, which is continuous with the zygomatic arch; (iii) the alveolar process, which bears the teeth; and (iv) the palatine process, which forms the roof of the mouth and floor of the nasal cavity. 10 Radiological Anatomy Faculty of Applied Health Sciences Technology The body of the maxilla is roughly pyramidal in shape, with its apex projecting superomedially between the orbit and nasal cavity. It houses the maxillary sinus. Radiology of the nasal cavity and paranasal sinuses Plain films: The frontal sinuses are not visible on the skull radiograph until the age of 2 years and achieve adult proportions by the age of 14. Asymmetry is common, and one or both may fail to develop. Development of the ethmoids occurs at a rate similar to that of the frontal sinuses. Pneumatization of the sphenoid sinus commences at 3 years of age and may extend into the greater wings of sphenoid or clinoid processes. The maxillary sinuses are the first to appear and are visible radiologically from a few weeks after birth. Computed tomography and MRI: CT scanning in either axial or coronal planes provides excellent visualization of the paranasal sinuses. Particular attention is paid to the region of the osteomeatal complex, where the maxillary, frontal and anterior ethmoidal sinuses drain, and the sphenoethmoid recess and superior meatus, on to which the sphenoid and posterior ethmoid sinuses drain. The pneumatized sinuses should contain nothing but air. MRI is surprisingly good at demonstrating the sinuses, as the bony septa, which have no signal themselves, are lined by high-signal mucosa. The bone is seen as a low intensity structure sandwiched between high- intensity mucosal layers. Air is also of low signal intensity. 11 Radiological Anatomy Faculty of Applied Health Sciences Technology THE MANDIBLE AND TEETH The mandible : The mandible is composed of two halves united at the symphysis menti. Each half comprises a horizontal body and a vertical ramus joined at the angle of the mandible. The ramus has two superior projections, the coronoid process anteriorly and the condylar process posteriorly, separated by the mandibular (or condylar) notch. The coronoid process gives attachment to the temporalis muscle, and the condylar process (or head of mandible) articulates with the base of the skull at the temporomandibular joint. The body of the mandible bears the alveolar border with its 16 tooth sockets. The temporomandibular joint: This is a synovial joint between the condyle of the mandible and the temporal bone. The temporal articular surface consists of a fossa posteriorly, the temporomandibular fossa, and a prominence anteriorly, the articular tubercle. The head of the mandible sits in the fossa at rest and glides anteriorly on to the articular tubercle when fully open. The joint is least stable during occlusion. The articular surfaces are covered with fibrous cartilage. In addition, a fibrocartilaginous disc divides the joint into separate smaller upper and larger lower compartments, each lined by a synovial membrane. The disc is described as having anterior and posterior bands with a thin zone in the middle and is attached to the joint capsule. No communication between joint compartments is possible unless the disc is damaged. 12 Radiological Anatomy Faculty of Applied Health Sciences Technology THE ORAL CAVITY AND SALIVARY GLANDS The oral cavity: This forms a passage from the lips to the oropharynx. It is largely filled by the tongue and teeth and is lined by a mucous membrane. The parotid gland opens on to its lateral wall, and the submandibular and sublingual glands open on to its floor. The roof is formed by the hard palate anteriorly and the soft palate posteriorly. The soft palate is a mobile flap that hangs posteroinferiorly at rest, separating the oro- from the nasopharynx. Two muscles insert into it from the lateral wall of the pharynx - the levator and the tensor veli palatini. These elevate the soft palate during swallowing to prevent reflux into the nose. The uvula hangs from the middle of the soft palate, and two pairs of muscles, the palatoglossus and the palatopharyngeus, run from its base to the tongue and pharynx. These muscles and their overlying mucosa form the anterior and posterior fauces, in whose concavity the palatine tonsils lie. The muscles of the tongue form two groups. The intrinsic group are arranged in various planes and alter the shape of the tongue. The extrinsic group are paired muscles that move the tongue and have attachments outside it. The floor of the mouth is formed by other muscles that also support the tongue. The most important is the mylohyoid muscle, which is slung from the mylohyoid line on the inner surface of the mandible to the hyoid bone on either side. Radiology of the oral cavity: 13 Radiological Anatomy Faculty of Applied Health Sciences Technology Because the oral cavity is amenable to direct vision, radiological assessment is not often required. However, in the case of infiltrating pathology such as tumours, cross sectional imaging using CT or magnetic resonance imaging (MRI) is very useful. MRI has inherently better soft tissue contrast than CT and can image in coronal and sagittal as well as axial planes. There is no artefact from the mandible or dental amalgam, and so MR images are superior to CT in this area. The salivary glands These exocrine glands are situated symmetrically around the oral cavity and produce saliva. The parotid gland: This is the largest of the salivary glands and lies behind the angle of the jaw and in front of the ear. It is molded against the adjacent bones and muscles. The gland has a smaller deep part and a larger superficial part, both of which are continuous around the posterior aspect of the ramus of the mandible via the isthmus. The parotid duct (Stensen's duct) begins as the confluence of two ducts in the superficial part of the gland and runs anteriorly deep to the gland. It arches over the masseter muscle before turning medially to pierce buccinators and drain into the mouth opposite the second upper molar. The duct is approximately 5 cm long. The submandibular gland: This gland lies in the floor of the mouth medial to the angle of the mandible. It is a mixed mucinous and serous gland. It has a lower 14 Radiological Anatomy Faculty of Applied Health Sciences Technology superficial lobe continuous with a smaller deep lobe above around the posterior border of the mylohyoid muscle. The submandibular (Wharton's) duct is about 5 cm long and commences as a confluence of several ducts in the superficial (lower) lobe. From here it runs superiorly through the deep (upper) lobe before running forward in the floor of the mouth to open at the side of the frenulum of the tongue. The sublingual gland: This small gland lies submucosally just anterior to the deep lobe of the submandibular gland and drains via several ducts (up to 20) directly into the floor of the mouth posterior to the opening of the submandibular gland. Radiology of the salivary glands Sialography: The ducts of the parotid and submandibular glands may be cannulated and injected with radio-opaque contrast to outline the ductal system. Cross-sectional imaging CT and MRI are of particular value for tumours of the glands, to assess involvement of surrounding structures. CT may be performed after sialography to improve visualization of the ducts. Ultrasound This may be performed through the skin or intraorally with high- frequency transducers. Nuclear imaging Because the salivary gland accumulates and secretes technetium-99m (99mTc) used in nuclear imaging, this can be used to image several 15 Radiological Anatomy Faculty of Applied Health Sciences Technology glands at once without cannulating the ducts. Graphs of uptake and excretion of the agent by individual glands may be computed. THE ORBITAL CONTENTS : The orbit contains the lacrimal gland, the globe, the extraocular muscles (including levator palpebrae), the optic nerve and the ophthalmic vessels. The whole is embedded in fat. The orbit is limited anteriorly by the orbital septum. The globe of the eye is composed of a transparent anterior part covered by the cornea, and an opaque posterior part covered by the sclera. These are joined at the corneoscleral junction, known as the limbus. The anterior and posterior extremities of the globe are known as the anterior and posterior poles. Anteriorly, a mucous membrane known as the conjunctiva covers the anterior aspect of the eye. It is reflected from the inner surface of the eyelids and fuses with the limbus. There are six extrinsic ocular muscles that insert into the sclera. The four rectus muscles, the superior, inferior, medial and lateral recti, arise from a common tendinous ring called the annulus of Zinn. This is attached to the lower border of the superior orbital fissure. These muscles insert into the corresponding aspects of the globe. The superior oblique arises from the sphenoid bone superomedial to the optic foramen. It then passes posteriorly to insert into the upper outer surface of the globe, posterior to the equator. The inferior oblique arises from the anterior part of the floor of the orbit and inserts into the lower outer part of the globe, behind the equator. The levator palpebrae superioris is also within the anterior fascial limit of the orbit, arising from the inferior surface of the lesser wing of sphenoid 16 Radiological Anatomy Faculty of Applied Health Sciences Technology and inserting into the tarsal plate of the upper eyelid behind the orbital septum. The arterial supply of the orbit is from the ophthalmic artery. The venous drainage of the orbit is through the superior and inferior ophthalmic veins into the cavernous sinus. The optic nerve is a direct extension of the brain. It is myelinated and has external coverings of dura, arachnoid and pia, forming its own subarachnoid space continuous with that of the brain. Internal anatomy and coverings of the eye: The globe of the eye is composed of three layers. The outermost consists of the tough white sclera posteriorly and the transparent cornea anteriorly. The junction of the sclera and cornea is called the limbus. The middle layer is a vascular layer known as the uveal tract. It consists of choroid posteriorly, and the ciliary body and iris anteriorly. The innermost layer is the retina, which contains the rods and cones. The anterior segment of the eye is that part anterior to the lens. It is divided into two chambers. The anterior chamber is between the cornea and iris, and the posterior chamber is between the iris and lens. The two chambers are filled with aqueous humour and are continuous through the aperture of the iris (the pupil). The posterior segment is behind the lens and is filled with a gelatinous fluid known as the vitreous body. Radiology of the orbit and eye Plain films The orbital margins may be assessed by plain radiography and are well seen on OF20, OM and OM30 views of the facial bones. Ultrasound 17 Radiological Anatomy Faculty of Applied Health Sciences Technology Ultrasound of the eye using high-frequency transducers (5-20 MHz) can demonstrate its internal anatomy. Computed tomography CT is an excellent modality for demonstrating the extraocular contents of the orbit. The lacrimal gland, extraocular muscles, globe, optic nerve and superior ophthalmic vein are routinely seen on sections obtained at 4 mm intervals. The bony walls of the orbit are demonstrated, and the foramina of the orbit and related anatomy are readily assessed. Coronal images are best for assessment of the orbital floor, especially in trauma. Magnetic resonance imaging MRI demonstrates the soft tissues of the orbit. It may be performed in any plane. It is of particular value in demonstrating the optic nerve, allowing excellent visualization of the entire nerve. THE EAR : The external ear The external ear consists of the pinna and the external auditory meatus. The external meatus is 3. 5 cm long and runs medially to the ear drum or tympanic membrane. The outer part of the canal is cartilaginous and the medial two thirds is bony. The entire canal is lined by skin. The middle ear 18 Radiological Anatomy Faculty of Applied Health Sciences Technology The middle ear is a slit-like cavity housed in the petrous bone. It lies between the tympanic membrane laterally and the inner ear medially. It has an upper part, which is recessed superiorly into the petrous bone and is known as the epitympanic recess or attic, as it lies at a higher level than the tympanic membrane. The roof of the cavity is formed by a thin layer of bone called the tegmen tympani, separating it from the middle cranial fossa and temporal lobe of the brain. The attic communicates with the mastoid air cells through a narrow posterior opening called the aditus ad antrum. A tiny spur of bone, the scutum, separates the external auditory canal and the antrum, where the tympanic membrane is attached. The lower part of the middle ear contains the ossicles, and is continuous inferiorly with the eustachian tube, which opens into the lateral wall of the nasopharynx. This tube is 3.5 cm long, bony at first, and cartilaginous in its lower portion. The floor of the middle ear is a thin plate of bone separating the cavity from the bulb of the jugular vein. The lateral wall of the cavity is the tympanic membrane and the ring of bone to which it is attached. The inner ear This is a membranous system of fluid-filled sacs concerned with hearing and balance. It is housed in a protective labyrinth of dense bone and lies in the petrous bone medial to the middle ear. The bony labyrinth consists of a vestibule, which communicates posteriorly with the three semicircular canals, and anteriorly with the spiral cochlea. The internal auditory meatus: 19 Radiological Anatomy Faculty of Applied Health Sciences Technology This bony canal is about 1 cm long and transmits the seventh and eighth cranial nerves from the posterior cranial fossa. Its lateral extent is separated from the inner ear by a perforated plate of bone. Radiology of the middle and inner ear Plain films The internal acoustic meati and parts of the bony labyrinth of the inner ear may be identified on a straight OF skull projection. These images and tomography have been superseded by CT and MRI for evaluation of the IAM. Computed tomography Images may be obtained in both axial and coronal planes. The internal auditory meati are readily assessed, and the extent of any pathology and its relationship to other important intracranial structures may be determined. High-resolution scanning of the temporal bone can image the cochlea, vestibule, semicircular canals, ossicles and bony canal of the facial nerve in axial or coronal planes. Magnetic resonance imaging MRI may also be used to study the contents of the temporal bone and has the advantage of being able to image in any plane. Coronal images demonstrate the contents of the internal auditory canal. THE PHARYNX AND RELATED SPACES 20 Radiological Anatomy Faculty of Applied Health Sciences Technology The pharynx is a muscular tube extending from the base of the skull to the level of the cricoid cartilage, approximately C6, where it is continuous with the oesophagus. It lies behind, and communicates with, the nasal and oral cavities, providing a common entrance to the respiratory and gastrointestinal tracts. The pharynx has three coats. Innermost is the mucous coat, which is continuous with the mucosa of the oral and nasal cavities. The submucous layer is the pharyngobasilar fascia and forms a thick fibrous coat, which gives the pharynx its shape. It is attached superiorly to the base of the skull and is continuous with the fibrous material filling the foramen lacerum. It is pierced only by the Eustachian tube. The outermost coat is formed by the three constrictor muscles. THE NASOPHARYNX AND RELATED SPACES The nasopharynx The nasopharynx is that part of the pharynx between the posterior choanae and the lower limit of the soft palate. It communicates anteriorly with the nasal cavity and inferiorly with the oropharynx. The roof of the nasopharynx is bound to the inferior surface of the sphenoid and clivus by the pharyngobasilar fascia. It has the parapharyngeal space and the deep soft tissues of the infratemporal space laterally. Posteriorly it lies on the upper cervical vertebrae and longus collis and capitus, and posterolaterally the styloid muscles separate it from the carotid sheath. The eustachian tube opens on to the lateral wall of the nasopharynx on either side, piercing the pharyngobasilar fascia. Spaces related to the nasopharynx 21 Radiological Anatomy Faculty of Applied Health Sciences Technology The parapharyngeal space is a slit-like space just lateral to the nasopharynx extending down from the base of the skull. The infratemporal space lies lateral to the nasopharynx and paranasopharyngeal space behind the posterior wall of the maxilla. It extends from the base of the skull to the hyoid bone. The oropharynx and laryngopharynx The oropharynx is the part of the pharynx that extends from the lower part of the soft palate to the epiglottis. It is continuous through the posterior fauces with the oral cavity and with the laryngopharynx below. It is lined by mucosa which is continuous with that of the oral cavity and nasopharynx. The laryngopharynx is the part of the pharynx that lies behind the larynx. It extends from the level of the epiglottis to the level of C6, where it continues as the oesophagus. The upper laryngopharynx is moulded around the proximal part of the larynx, forming two deep recesses on either side known as the piriform fossae. Radiology of the pharynx Plain films Lateral views of the skull and neck demonstrate the soft tissue outlines of the pharynx and lateral tomography gives improved separation of the soft-tissue planes. 22 Radiological Anatomy Faculty of Applied Health Sciences Technology The posterior and lateral walls of the nasopharynx may be identified on the basal skull projection and the piriform fossae of the laryngopharynx are seen on AP views of the neck. Cross-sectional imaging CT and MRI provide excellent detail of the pharynx, its fascial planes and its related spaces. Images are usually obtained in the axial plane. Coronal images may also be obtained by both modalities but are easier to obtain using MRI, as this may be performed without moving the patient. Imaging in both axial and coronal planes is necessary to evaluate the base of the skull. CT yields excellent axial images of the base of the skull and provides good bone detail. Both CT and MRI demonstrate the muscles and soft-tissue planes and the examinations are complementary. THE LARYNX The larynx forms the entrance to the airway and is responsible for voice production. It extends from the base of the tongue to the trachea, lying anterior to the third to sixth cervical vertebrae. It lies between the great vessels of the neck and is covered anteriorly by the strap muscles of the 23 Radiological Anatomy Faculty of Applied Health Sciences Technology neck, fascia and skin. It is lined by mucosa, which is continuous with that of the pharynx above and the trachea below. Its framework is composed of three single and three paired cartilages, which articulate with each other and are joined by muscles, folds and connective tissue. -The anchor cartilage of the larynx is the cricoid cartilage This is shaped like a signet ring, with a flat, wide lamina posteriorly and an arch anteriorly. It is joined to the thyroid cartilage above by the cricothyroid membrane, and to the trachea below by the cricotracheal membrane. -The paired pyramidal arytenoid cartilages sit on the superolateral margin of the signet posteriorly. These bear anteroinferior vocal processes, which give rise to the vocal ligaments of the true vocal cords. -The thyroid cartilage forms the anterior and lateral boundary of the larynx. It is formed by a pair of laminae, which are joined anteriorly forming an angle and are separated above to form the superior thyroid notch. This notch is at approximately C4 level. The posterior parts of the laminae have upper and lower projections known as the superior and inferior horns or cornua. -The epiglottis is a leaf-shaped cartilage whose narrow base or petiole is attached to the inner surface of the thyroid cartilage. Radiology of the larynx : Plain radiography This is a relatively simple method of demonstrating the anatomy of the larynx. 24 Radiological Anatomy Faculty of Applied Health Sciences Technology Lateral views are the most useful as the larynx is not obscured by overlying bone. The air in the pharynx and larynx provides intrinsic contrast with the soft-tissue walls and mucosal folds. Tomography This is useful in the AP plane when overlying bony densities are blurred to allow better detail. The true and false cords and laryngeal ventricle are best seen in this view. The piriform fossae are seen on either side of the proximal larynx, between it and the thyroid cartilage. CT and MRI Cross-sectional imaging using CT provides excellent anatomical detail of the larynx and surrounding structures. Scans are usually obtained in the axial plane, but with MRI sagittal and coronal imaging is also possible. Section 3:Neuro-anatomy *Computed tomography (CT) and magnetic resonance imaging ( MRI) are the mainstays of cerebral imaging. 25 Radiological Anatomy Faculty of Applied Health Sciences Technology *Skull radiography now plays very little part in diagnosis, being largely replaced by multislice CT. *Non- or minimally invasive angiography performed using CT ( CT angiography) or MRI ( magnetic resonance angiography) has resulted in invasive catheter angiography being reserved for a few special diagnostic indications or as part of an interventional, (therapeutic), procedure. *Anatomical detail is far better displayed by MRI than by CT, although both are valuable in clinical practice. *With T1-weighted (T1W) MR images, grey matter is of lower signal intensity (darker) than white matter. *On T2-weighted (T2W) images, including T2-FLAIR sequences, the reverse is true. *With CT, somewhat paradoxically, white matter is depicted as darker grey than grey matter. The explanation is that CT is an X-ray investigation. White matter contains lipid as part of myelin, which is relatively radiolucent. *The lipid in subcutaneous fat is typically high signal (white) on both T1 and T2 MR sequences. Conversely, lipid is extremely radiolucent and appears black on CT. *Dense bone contains few free protons on which MRI is based and therefore appears as a signal void (black) on MR. On CT, bone, which is radio-opaque, appears white. 26 Radiological Anatomy Faculty of Applied Health Sciences Technology *Air in the paranasal sinuses appears black on both CT and MRI. Besides compact bone and air, hypointensity on MRI occurs also with iron deposition and as a feature of rapid blood or CSF flow. *The intravenous contrast agents used in CT and MRI do not cause significant cerebral parenchymal enhancement, when the blood–brain barrier is intact. Iodinated contrast agents administered intravenously for CT enhance blood within the cranial arteries and veins and dural venous sinuses. Enhancement is seen also in the highly vascular choroid plexuses and in those structures outside the blood–brain barrier such as the pituitary gland and infundibulum. *With MRI the mechanism of contrast enhancement with intravenous gadolinium DTPA is quite different from CT, but nevertheless, on T1W images, those structures which enhance become hyperintense (whiter) in much the same way as with CT. *One notable difference, however, is in the depiction of rapidly flowing blood with MRI, which appears as a ‘signal void’ (black) and does not enhance. This principle applies also to CSF, which can flow rapidly through the cerebral aqueduct, causing a signal void seen particularly on T2W axial images. The cerebral envelope *The meninges invest the brain and spinal cord. The three constituent parts are the outer, fibrous dura mater, the avascular, lattice-like arachnoid mater and the inner, vascular layer, the pia mater. 27 Radiological Anatomy Faculty of Applied Health Sciences Technology *The outer layer is the periosteum of the inner table of the skull (the endosteum). The inner layer covers the brain and gives rise to the falx and tentorium. Dura is hyperdense on CT images and relatively hypointense on MRI. It shows contrast enhancement on both modalities and since the falx may calcify or ossify, MRI may demonstrate focal regions of signal void due to calcification or of hyperintensity due to fat within marrow. *The falx is a sickle-shaped fold of dura, comprising two layers, which forms an incomplete partition between the cerebral hemispheres. It extends from the crista galli to the internal occipital protuberance, where it joins the tentorium and is thinner anteriorly. The falx is demonstrated as a midline linear density on axial CT scan near to the vertex, but inferiorly and posteriorly assumes a triangular shape conforming to the superior sagittal sinus in cross-section. *The tentorium cerebelli, another double dural fold, is attached from the posterior clinoid processes along the petrous ridges to the internal occipital protuberance. Its upper, free, medial border surrounds the midbrain. The brainstem and cranial nerves The brainstem consists of the midbrain, pons and medulla. Even high field strength MRI shows little internal detail under normal scanning conditions. The cerebellum *The cerebellum lies posterior to the brainstem, to which it is connected by the cerebellar peduncles. The cortical mantle overlies the white matter 28 Radiological Anatomy Faculty of Applied Health Sciences Technology core as in the cerebral hemispheres but the cerebellar cortical ridges, known as the folia, and the intervening sulci are approximately parallel to one another. *The cerebellum consists of a narrow midline vermis and two hemispheres. The pituitary gland *The pituitary gland occupies the pituitary fossa in the body of the sphenoid bone, situated in the midline above the sphenoid sinus in between the cavernous sinuses. It is suspended from the pituitary stalk, or infundibulum. The basal ganglia *The basal ganglia comprise several deep grey matter nuclei within the forebrain, midbrain and diencephalon: caudate nucleus putamen globus pallidus (also referred to as the pallidum) subthalamic nucleus substantia nigra. The cerebral hemispheres *The cerebral cortex is organized into folds called gyri between which there are CSF-filled grooves called sulci. The deeper and more anatomically constant sulci are known as fissures. The lateral (Sylvian) 29 Radiological Anatomy Faculty of Applied Health Sciences Technology fissure marks the superior margin of the temporal lobe, while the parieto- occipital fissure divides the parietal and occipital lobes. *The insula is an area of invaginated cortex lying deep within the Sylvian fissure, covered by the frontal, temporal and parietal opercula. Frontal lobe Anterior to central sulcus Parietal lobe Posterior to central fissure Lies above and in front of occipital lobe (divided by parietooccipital fissure. Temporal lobe Inferior to lateral (Sylvian) fissure Occipital lobe Posterior to parieto-occipital fissure The ventricular system *The cerebral ventricles are cavities situated deep within the brain. They are lined by ependymal cells and contain the choroid plexus, which produces CSF. There are four ventricles in total: the two paired lateral ventricles and the midline third and fourth ventricles. *Each lateral ventricle drains into the third ventricle via the foramen of Monro. The third ventricle communicates with the fourth via the cerebral aqueduct (of Sylvius). 30 Radiological Anatomy Faculty of Applied Health Sciences Technology *Each lateral ventricle has a body, atrium and three horns named after the lobe in which they lie: frontal, occipital, temporal. Section 4: Anatomy of the chest Imaging modilities *The chest radiograph (CXR) It is used for the initial assessment of the lungs, mediastinum and bones. Posteroanterior (PA) view – patient upright, on full inspiration with the scapulae moved laterally, so that the lungs are not obscured Lateral view Anteroposterior (AP) view – patient either supine or sitting; on this view there is magnification of the heart and mediastinum and the clavicles obscure the lung apices 31 Radiological Anatomy Faculty of Applied Health Sciences Technology Apical lordotic view – the X-ray beam is angled superiorly 15–20° so the clavicles and first ribs are projected above the lung apices Expiration films are used to assess air trapping. Cross-sectional imaging Computed tomography (CT) *CT provides improved spatial resolution because of lack of overlap of structures. The use of intravenous contrast medium improves the demonstration of vessels. *Multidetector CT produces excellent multi planar reformats and other post-processing can be undertaken. The data are viewed at different windows and levels for air and soft tissue. MRI *MRI provides excellent contrast resolution and increased soft tissue resolution. *It is valuable for assessing the heart, mediastinum, hilar, diaphragm and chest wall The chest consists of the bony skeleton of the spine and ribs, the chest wall and diaphragm, the mediastinum and great vessels, the airways, lung parenchyma and pulmonary vessels. Bony thorax Consists of the thoracic spine, ribs, sternum and clavicle. Thoracic spine Consists of 12 vertebrae: body with facets for articulation of the ribs on the lateral aspect 32 Radiological Anatomy Faculty of Applied Health Sciences Technology neural arch surrounding vertebral canal, made up of a pedicle and lamina on each side, a posterior spinous process and bilateral transverse processes, which have a facet for articulating with the tubercles of the ribs (except T11 and 12). The pedicle forms the intervertebral foramen with its adjacent vertebra and the nerve root pair exit caudal to the corresponding vertebra. Ribs The typical rib A typical rib has a head, neck, tubercle and shaft. The head has two facets for articulation with vertebral bodies, for example the sixth rib articulates with the bodies of T5 and T6 vertebrae. These costovertebral joints are synovial joints. The neck of the rib is attached by a ligament to the transverse process of the vertebra above. The tubercle has a facet medially for articulation with its own transverse process. The tubercle also has a non articular part laterally for ligament attachment. The shaft has a posterior angle and a much less prominent anterior angle. It has a subcostal groove that is much more prominent posteriorly. This lodges the intercostal vessels and nerves. Atypical ribs First rib This is the shortest, flattest and most curved rib. It articulates with T1 only. A tubercle on its inner border marks the attachment of the scalenus anterior muscle. Twelfth rib This has only one articular facet on its head; it has no tubercle and no subcostal groove. 33 Radiological Anatomy Faculty of Applied Health Sciences Technology Second rib This is less curved and twice as long as the first rib. Tenth rib This differs from the typical ribs by having only one articular facet on its head. Eleventh rib This also has only one articular facet on its head. It has no tubercle for articulation with the transverse process. Sternum: Consists of: manubrium – provides articulation for clavicles 1st and upper part of 2nd ribs body – consists of four parts, which fuse by the age of 25 and articulate with 2nd–7th costal cartilages; the junction of the body with the manubrium (angle of Louis) is at T4/5 xiphoid process – often remains cartilaginous. Clavicle Articulated medially with the manubrium at the sternoclavicular joint Articulated laterally with the acromion at the acromioclavicular joint and also attached to the coracoid process subclavian vessels and trunks of brachial plexus pass behind the medial third Costal cartilages These are the unossified anterior ends of the ribs. They slope upwards to the sternum, where they form synovial sterno¬chondral joints (except the first, which forms a primary cartilaginous joint with the sternum). 34 Radiological Anatomy Faculty of Applied Health Sciences Technology The costal cartilages of the first seven ribs articulate with the sternum. The eighth to tenth ribs articulate with the costal cartilages of the ribs above. The eleventh and twelfth costal cartilages have pointed ends and end in the muscles of the abdominal wall. The intercostal space and vessels This is bridged by the muscles - the external, internal and innermost intercostal muscles. The neurovascular bundle lies between the internal and innermost muscle layers. Intercostal arteries Posterior Upper two spaces supplied by superior intercostal arteries from the costocervical branch of the subclavian artery; Lower nine from the thoracic aorta. Anterior Two branches to most intercostal spaces: — Upper six spaces supplied by the internal thoracic branch of the subclavian artery; — Next three by the musculophrenic artery, the continuation of the internal thoracic artery. The lower two spaces have no anterior intercostal artery. Intercostal veins Posterior First intercostal vein arches over the pleura to drain into the brachiocephalic vein; Second to fourth drain to a superior intercostal vein which drains to the azygos vein on the right and to the brachiocephalic vein on the left; Fifth to eleventh on the right drain to the azygos vein; 35 Radiological Anatomy Faculty of Applied Health Sciences Technology Left fifth to eighth drain to the accessory hemiazygos vein and ninth to eleventh to the hemiazygos vein. Anterior Veins accompany arteries to internal thoracic and musculophrenic veins. Muscles of the thoracic cage The external, internal and innermost intercostal muscles occupy the spaces between the ribs. Subcostal muscles on the deep surface of the lower ribs span two or three ribs. The innermost intercostals and the subcostals separate the intercostal neurovascular bundles from the pleura. The transverse thoracic muscle arises on the deep surface of the sternum and adjacent lower costal cartilages and passes superolaterally to the deep surface of the anterior ribs. Superficial to the ribs three muscle groups posteriorly: the costal levators, serratus posterior superior; and serratus posterior inferior. Other muscles have attachments to the thoracic cage and can be seen on axial cross-sectional imaging, including the pectoral muscles anteriorly, the serratus anterior and the teres major and subscapularis laterally and posteriorly, and the rhomboids, the erector spinae and trapezius posteriorly. Diaphragm Separates the thorax from the abdomen. It consists of a peripheral muscular part arising from margins of thoracic outlet right crus arises from the front of vertebral bodies of L1–3 left crus from vertebral bodies of L1–2 arcuate ligament from the fascia of the psoas and quadratus lumborum 36 Radiological Anatomy Faculty of Applied Health Sciences Technology attachments to the lower 6th ribs and sternum central tendon, which is partly fused to the pericardium. There are three main openings: Aortic – (T12) – transmitting the aorta, thoracic duct and azygous vein Oesophageal (T10) – oesophagus, left gastric artery and vein and vagus Vena cava (T8) – inferior vena cava and right phrenic. The right hemidiaphragm is usually 1–1.5 cm higher than the left , but may be at the same level. THE PLEURA : The pleura is a serous membrane that: (i) covers the lung (i. e. the visceral pleura); and (ii) lines the thoracic cavity and mediastinum (i. e. the parietal pleura). Parts of the pleura are named according to site, for example costal, diaphragmatic, mediastinal and apical. The visceral and parietal layers are continuous with each other anterior and posterior to the lung root, but below the hilum the two layers hang down in a loose fold called the pulmonary ligament. The visceral pleura extends into interlobar and accessory fissures. The parietal pleura is supplied by the systemic vessels. The visceral pleura receives arterial supply from both the bronchial and the pulmonary circulation. Airways The airways consist of the trachea, bronchi, bronchioles and distal small airways. Trachea 37 Radiological Anatomy Faculty of Applied Health Sciences Technology 9–12 cm in length. It commences at the level of the cricoid (C6) and bifurcates at the carina (T5), passing from the midline to the right. The intrathoracic portion measures 6–9 cm The transverse diameter is 10–21 mm in women and 13–25 mm in men, the sagittal diameter 10–23 mm in women and 13–27 mm in men There are 12–16 incomplete cartilaginous rings. The posterior wall is fibrous tissue. Rings may calcify in older people Relations of the trachea Cervical Anterior: — Isthmus of thyroid anterior to the second, third and fourth rings — Inferior thyroid veins — Strap muscles: sternohyoid and sternothyroid; Posterior: oesophagus and recurrent laryngeal nerves; Lateral: lobes of thyroid gland — Common carotid artery. Thoracic The thoracic relations are as follows: Anterior: — Brachiocephalic and left common carotid arteries — Left brachiocephalic vein Posterior: oesophagus and left recurrent laryngeal nerve Left lateral: — Arch of the aorta — Left common carotid and left subclavian arteries; and Right lateral: right brachiocephalic artery — Right vagus nerve 38 Radiological Anatomy Faculty of Applied Health Sciences Technology — Arch of the azygos vein — Pleura (in direct contact unlike the other side). Blood supply of the trachea The upper trachea is supplied by the inferior thyroid artery and the lower part is supplied by branches of the bronchial artery. Venous drainage is to the inferior thyroid venous plexus. Main bronchi Carina This is the anteroposterior ridge at the junction of the main bronchi. It lies at T5 vertebral level (T4 on inspiration and T6 on expiration) and at the level of the sternal angle. The carinal angle measures approximately 65° - that is, 20° to the right of the midline and 40° to the left. This angle is slightly larger in children. Relations The relations of the right main bronchus are as follows: Anterior: — Superior vena cava — Right pulmonary artery; Posterior: azygos vein; and Superior: arch of azygos vein. The right main bronchus (eparterial bronchus) The right main bronchus lies at about 25° to the median plane. It is 2. 5 cm long and 1. 5 cm wide. It is thus wider, shorter and more vertical than the left main bronchus. The bronchus to the upper lobe arises almost immediately after the tracheal bifurcation, entering the hilum of the lung separately and thereafter dividing into anterior, apical and posterior bronchi. The right 39 Radiological Anatomy Faculty of Applied Health Sciences Technology bronchus continues as the bronchus intermedius, which then divides into middle- and lower-lobe bronchi. The middle-lobe bronchus has medial and lateral divisions. The apical segment bronchus of the lower lobe comes off opposite the bronchus to the middle lobe. The lower-lobe bronchus divides into four basal segment bronchi - posterior, lateral, anterior and medial. Left main bronchus (hyparterial bronchus) The left main bronchus lies at 40° to the median plane. It is 5 cm long and 1. 2 cm in diameter. Relations The relations of the left main bronchus are as follows: Anterior: pulmonary trunk; Posterior — Oesophagus — Descending aorta; and Superior: — Aortic arch — Pulmonary artery. The left main bronchus divides into upper- and lower lobe bronchi within the lung. The upper-lobe divisions are similar to the right. The posterior and apical segmental bronchi usually have a common apicoposterior bronchus, which then subdivides. The lingular lobe bronchus comes off the upper-lobe bronchus and has superior and inferior divisions. The lower-lobe bronchus has apical, lateral, anterior and posterior basal segments but no medial basal segment. Blood supply 40 Radiological Anatomy Faculty of Applied Health Sciences Technology Whereas the lungs receive the entire output of the right heart, their own nutritive supply arises from the bronchial arteries, branches of the thoracic aorta. The bronchial veins drain on the right to the azygos system and on the left to the hemiazygos system. THE LUNGS The lungs are described as having costal, mediastinal, apical and diaphragmatic surfaces. The right lung has three lobes and the left has two, with the lingula of the left upper lobe corresponding to the right middle lobe. Lobar anatomy: The right lung is larger than the left and has 3 lobes; the left lung has 2 lobes. There are 10 segments in the right lung and 8 in the left and they are named after the bronchi. Right upper lobe – three segments: · apical · posterior – abuts the superior oblique fissure and the posteromedial horizontal fissure · anterior – abuts the horizontal fissure, the anterior lateral costal margin and the mid anterior mediastinum. Right middle lobe – two segments · medial – abuts the right heart border · lateral – abuts the oblique fissure and the horizontal fissure. Right lower lobe – five segments · superior · medial basal · anterior basal · lateral basal 41 Radiological Anatomy Faculty of Applied Health Sciences Technology · posterior basal. Basal segments abut the right hemidiaphragm. Left upper lobe – four segments · apico-posterior · anterior. Abuts the superior mediastinum. lingula – superior inferior. Abuts the left heart border. Left lower lobe – four segments · superior · anterior basal · lateral basal · posterior basal. Abuts the descending aorta (superior and/or posterior basal) and the left hemidiaphragm. Interlobar fissures The depth of fissures varies from a superficial slit to complete separation of lobes. The oblique (major) fissure This is similar in both right and left lungs. It extends from T4/T5 posteriorly to the diaphragm anteroinferiorly. The left major fissure is more vertically orientated than the right. The transverse (minor) fissure This separates the upper and middle lobes of the right lung. It runs horizontally from the hilum to the anterior and lateral surfaces of the right 42 Radiological Anatomy Faculty of Applied Health Sciences Technology lung at the level of the fourth costal cartilage. It is anatomically complete in only one-third of subjects and is absent in 10%. Left transverse fissure This is found in 18% of postmortem specimens but is rarely seen on chest radiographs. The pulmonary artery The pulmonary trunk leaves the fibrous pericardium and bifurcates almost at once in the concavity of the aortic arch anterior to the left main bronchus. The right pulmonary artery is longer than the left. It passes across the midline below the carina and comes to lie anterior to the right main bronchus. It bifurcates while still in the hilum of the right lung. An artery for the right upper lobe passes anterior to the right upper-lobe bronchus. The interlobar artery to the right middle and lower lobes passes with the bronchus intermedius. The left pulmonary artery spirals over the superior aspect of the left main bronchus to reach its posterior surface. It is attached to the concavity of the aortic arch by the ligamentum arteriosum. The pulmonary arteries further subdivide into segmental arteries that travel with the segmental bronchi, for the most part on their posterolateral surface. The pulmonary arteries supply only the alveoli. The pulmonary veins Two veins pass to each hilum – from lung tissue above and below each oblique fissure. These enter the mediastinum slightly below and anterior to the pulmonary arteries. On the right side the veins from the lobes may 43 Radiological Anatomy Faculty of Applied Health Sciences Technology remain separate, so that three veins leave the right lung and enter the left atrium. On the left side the two pulmonary veins may unite and enter the left atrium as a single vessel. The bronchial arteries The bronchial arteries supply the bronchi, the visceral pleura and the connective tissue of the lungs. They arise from the thoracic aorta in 90% of subjects, at T5 or T6 vertebral level in 80% of cases. There are usually one right and two left bronchial arteries. Bronchial arteries may also arise from the subclavian artery or from its internal thoracic branch. Tissues supplied by bronchial arteries drain to pulmonary veins or bronchial veins. Bronchial veins Bronchial veins form two distinct systems. The deep veins form a network of veins around the pulmonary interstitium and communicate freely with the pulmonary veins. They also form a bronchial vein trunk that drains to the pulmonary system. The superficial bronchial veins drain to the azygos vein on the right side and to the accessory hemiazygos vein on the left side. Lymphatics Mediastinal lymph nodes that drain the lung are named according to their position: Pulmonary nodes within the lung substance; Bronchopulmonary nodes at the hilum; Carinal nodes below the hilum; Tracheobronchial nodes above the tracheobronchial junction; and 44 Radiological Anatomy Faculty of Applied Health Sciences Technology Right and left paratracheal nodes on either side of the trachea. Lung roots The roots of the lungs are formed by the structures that enter and emerge at the hila. They lie at vertebral levels T5-T7. The right lung root lies below the arch of the azygos vein and posterior to the superior vena cava and the right atrium. The left lung root lies below the arch of the aorta and anterior to the descending aorta. THE MEDIASTINAL DIVISIONS : The mediastinum is the space between the lungs and their pleura. It is arbitrarily divided into superior, middle, anterior and posterior sections. These divisions are not anatomical. They are used to describe the location of pathological processes. The superior mediastinum is above a line drawn from the lower border of T4 to the sternal angle. Below this line are anterior, middle and posterior compartments. The middle mediastinum is occupied by the heart and its vessels. The anterior mediastinum is between the anterior part of the heart and the sternum. The posterior mediastinum is between the posterior part of the heart and the thoracic spine, extending down behind the posterior part of the diaphragm as it slopes inferiorly. The superior mediastinum contains the: Aortic arch and branches; 45 Radiological Anatomy Faculty of Applied Health Sciences Technology Brachiocephalic veins and superior vena cava Trachea; Oesophagus; Thoracic duct; Lymph nodes; and Nerves. The anterior mediastinum contains the: Thymus; Mammary vessels; and Lymph nodes. The posterior mediastinum contains the: Descending aorta; Oesophagus; Azygos venous system; Thoracic duct; and Para-aortic, oesophageal and paraspinal nodes. The middle mediastinum contains the: Heart and pericardium: Nerves; Lymph nodes; and Great vessels. THE HEART Gross anatomy and orientation 46 Radiological Anatomy Faculty of Applied Health Sciences Technology The heart is pyramidal in shape and lies obliquely in the chest. Its square- shaped base points posteriorly and the elongated apex to the left and inferiorly. The left atrium forms the base or posterior part, with the superior and inferior pulmonary veins draining into its four corners. The right atrium forms the right border, with superior and inferior venae cavae draining into its upper and lower parts. The apex and left border are formed by the left ventricle. The right ventricle forms the anterior part. The inferior (diaphragmatic) part of the heart is formed by both ventricles anteriorly and a small part of right atrium posteriorly where the IVC enters this chamber. The oblique orientation of the heart causes the ventricles to lie anterior and inferior to the atria. The heart is also rotated in a clockwise fashion about its axis, so that the right atrium and ventricle are at a slightly higher level than their left counterparts. The interatrial and interventricular septa are said to lie in the left anterior oblique plane. This means that the long axis of the septa runs anteriorly to the left. The tricuspid and mitral valves, which separate the right and left atria and ventricles respectively. Pericardium: This is a closed sac consisting of parietal and visceral layers that enclose a potential space which contains 20-25 mL of serous fluid. It is draped over the heart and great vessels. The visceral layer adheres to the myocardium and is also known as the epicardium. The parietal layer is free, except inferiorly, where it is bound 47 Radiological Anatomy Faculty of Applied Health Sciences Technology to the central tendon of the diaphragm, and superiorly where it fuses with the covering of the great vessels. The pericardial reflections, which are really the boundaries of the closed sac, are found posteriorly around the IVC and pulmonary veins where the space between the veins forms the oblique sinus of the pericardium. The pericardium extends superiorly for 2-3 cm over the ascending aorta and over the pulmonary artery almost to its bifurcation. It also extends for a short distance over the venae cavae and pulmonary veins. Some fat is present between the epicardium and myocardium. This increases with age. Fat is also present between the pericardium and mediastinal pleura. Section 4: Gastrointestinal tract *THE OESOPHAGUS* *This begins at the level of C5/C6 or the lower border of the cricoid cartilage as the continuation of the oropharynx. * Its upper limit is defined by the crico¬pharyngeus muscle, which encircles it from front to back. *It descends behind the trachea and thyroid, lying in front of the lower cervical vertebrae. *In the chest it passes behind the trachea, left main bronchus, left atrium and upper part of the left ventricle from above downward; it then passes behind the posterior sloping part of the diaphragm before traversing this at the level of T10. 48 Radiological Anatomy Faculty of Applied Health Sciences Technology *Below this level, its left side lies on left lung and pleural tissue. On its right side it is crossed by the termination of the azygos vein at the level of T4. Below this, the azygos vein lies behind and to its right and it is in contact with right lung and pleura. Posteriorly are the thoracic vertebrae and thoracic duct, the azygos vein and tributaries, and the right posterior intercostal arteries as these cross the vertebral column from the descending aorta. The descending aorta lies to its left side initially. Then, as the oesophagus passes forwards and to the left, it becomes anterior to this vessel in the mid thorax and anterior and to its left as it passes through the diaphragm. In its terminal part in the abdomen it is retroperitoneal and grooves the posterior aspect of the liver. It enters the stomach at the oesophago¬gastric junction. Blood supply *The blood supply is organized in thirds (with free anastomosis between each third) as follows: Branches of the inferior thyroid artery supply the upper third; Branches from the descending aorta supply the middle third; and Branches from the left gastric artery supply the lower third. *Venous drainage is also found in thirds: to the inferior thyroid veins, the azygos system, and to the portal system via the left gastric vein. Thus, there is communication of the systemic and portal venous systems in the oesophagus. Lymph drainage 49 Radiological Anatomy Faculty of Applied Health Sciences Technology This is via a rich paraoesophageal plexus to posterior mediastinal nodes, draining from here to supraclavicular nodes. The lower part drains to left gastric and coeliac nodes. If the oesophagus contains air, the posterior aspect of the anterior oesophageal wall may be seen on the lateral film, behind the trachea. This is known as the 'posterior tracheal stripe'. Barium studies The main radiological method of assessing the oesophagus is the barium- swallow technique, where the oesophagus is outlined by barium. Gas is usually swallowed in addition to give a double-contrast examination and to distend the oesophagus. The use of a paralyzing agent such as intravenous hyoscine butylbromide (Buscopan) stops intrinsic oesophageal contraction, allowing a better appreciation of oesophageal anatomy. On the frontal view, the oropharynx may be examined. The piriform fossae are outlined by barium and the epiglottis and base of the tongue show as filling defects in the midline. On the lateral view the tongue base and epiglottis are seen from the side, with the vallecula between. The cervical oesophagus is seen to lie on the anterior surface of the vertebral bodies of the cervical spine. In the chest, the oesophagus is best demonstrated with the subject rotated slightly off lateral - usually in the right anterior oblique position. In this position the oesophagus can be seen to curve anteriorly in its distal part to enter the stomach. Cross-sectional imaging 50 Radiological Anatomy Faculty of Applied Health Sciences Technology The oesophagus may also be imaged by CT and MRI. On cross-section its relationship to the other structures of the thorax is appreciated. Its visualization is improved if it contains air. When collapsed it is seen as a narrow, thin-walled structure in the posterior mediastinum. Appreciation of the areas in which air containing lung is adjacent to the oesophagus provides an understanding of the mediastinal lines seen on the frontal chest radiograph. THE STOMACH *The stomach is J-shaped but varies in size and shape with the volume of its contents, with erect or supine position, and even with inspiration and expiration. The size and shape of the stomach also vary considerably from person to person, differing especially with the build of the subject. *The stomach has two orifices - the cardiac orifice (so named because of proximity through the diaphragm to the heart) at the oesophagogastric junction, and the pylorus. It has two curvatures - the greater and lesser curves. The incisura is an angulation of the lesser curve. The part of the stomach above the cardia is called the fundus. Between the cardia and the incisura is the body of the stomach, and distal to the incisura is the gastric antrum. The lumen of the pylorus is referred to as the pyloric canal. *The stomach is lined by mucosa, which has tiny nodular elevations called the areae gastricae and is thrown into folds called rugae. Longitudinal folds paralleling the lesser curve are called the 51 Radiological Anatomy Faculty of Applied Health Sciences Technology 'magenstrasse' meaning 'main street'. Rugae elsewhere in the stomach are random and patternless. *There are three muscle layers in the wall of the stomach: (i) an outer longitudinal, (ii) an inner circular and (iii) an incomplete, innermost oblique layer. The circular layer is thickened at the pylorus as a sphincter, but not at the oesophagogastric junction. *Peritoneum covers the anterior and posterior surfaces of the stomach and is continued between the lesser curve and the liver as the lesser omentum, and beyond the greater curve as the greater omentum. Anterior relations of the stomach The upper part of the stomach is covered by the left lobe of the liver on its right and by the left diaphragm on the left. The fundus occupies the concavity of the left dome of the diaphragm. The remainder of the anterior of the stomach is covered by the anterior abdominal wall. Posterior relations of the stomach Posterior to the stomach lies the lesser sac. The structures of the posterior abdominal wall that are posterior to this are referred to as the stomach bed. The pancreas lies across the midportion of the stomach bed with the splenic artery partly above and partly behind it, and the spleen at its tail. Above the pancreas are the aorta and its coeliac trunk and surrounding plexus and nodes, the diaphragm, the left kidney and the adrenal gland. Attached to the anterior surface of the pancreas is the transverse mesocolon, which forms the inferior part of the stomach bed. 52 Radiological Anatomy Faculty of Applied Health Sciences Technology Arterial supply of the stomach Arteries reach the stomach along its greater and lesser curves from branches of the coeliac trunk as follows: The left gastric artery from the coeliac trunk. The right gastric artery from the hepatic artery. The short gastric arteries from the splenic artery. The left gastroepiploic artery from the splenic artery. The right gastroepiploic artery from the gastroduodenal branch of the hepatic artery. *The left gastric artery also supplies branches to the lower oesophagus. The arteries of the stomach anastomose freely within the stomach wall, unlike the arteries of the small and large intestine, where the vessels that enter the gut wall are end arteries. The venous drainage of the stomach The venous drainage of the stomach follows a similar pattern to the arterial supply: The right gastric vein drains to the portal vein. The left gastric vein drains to the splenic vein. The short gastric and left gastroepiploic veins drain to the splenic vein. The right gastroepiploic vein drains to the superior mesenteric vein. Lymph drainage of the stomach Lymph drainage also follows the arterial pattern and drains to nodes around the coeliac trunk: The left gastric artery drains directly to coeliac nodes. The right gastric artery drains via retroduodenal nodes to coeliac nodes. 53 Radiological Anatomy Faculty of Applied Health Sciences Technology The short gastric and left gastroepiploic arteries drain via nodes in the splenic hilum and behind the pancreas to coeliac nodes. The right gastroepiploic artery drains via retroduodenal nodes to coeliac nodes. The coeliac nodes drain to the cisterna chyli. Radiological features of the stomach Plain film of the abdomen If a radiograph is taken in the erect posture, a long fluid level is seen in the fundus. This is because the antrum and body contract when empty and a relatively small amount of fluid and gas in the fundus can produce a long fluid level. In a supine view, the gas in the rugae on the anterior wall of the stomach gives a linear pattern. On intravenous urography (IVU) studies the rugae may enhance with contrast on early films and should not be interpreted as a left renal or adrenal mass. Double-contrast barium-meal examination Features of the stomach, such as the greater and lesser curves, the incisura, the cardia, fundus, body, antrum and pylorus, can be seen. The change in position of these with posture and respiration can be appreciated on fluoroscopy. The areae gastricae can be seen as small nodular elevations of 2-3 mm in diameter. The rugae are 3-5 mm in thickness. These are effaced by gastroparetic agents such as glucagon or hyoscine butylbromide (Buscopan). The long rugae of the 'magenstrasse' paralleling the lesser curve can also be seen. 54 Radiological Anatomy Faculty of Applied Health Sciences Technology Compression views can only be obtained of that part of the stomach with the anterior abdominal wall as an anterior relation, that is, the lower body and the antrum. CT and MRI of the stomach The relationship of the stomach to the structures of the stomach bed, such as the pancreas, the aorta, the spleen and the left kidney and adrenal, can be seen. The mucosa of the stomach enhances with intravenous contrast and the stomach layers are best appreciated in the arterial phase of contrast enhancement, when there is no positive contrast in the stomach. Angiography of the coeliac trunk This is used to image the vessels that supply the stomach. The stomach can be filled with gas to eliminate confusing rugal patterns, and to push other bowel loops out of the field of interest. THE DUODENUM The duodenum extends from the pylorus to the duodenojejunal flexure, where transition to the small bowel proper is marked by the assumption of a mesentery. The first 2.5 cm of duodenum, like the stomach, is attached to the greater and lesser omentum. The remainder of the duodenum is retroperitoneal and, as a result, less mobile than the small intestine. Its anterior surface is covered by peritoneum, except where the second part is crossed by the transverse mesocolon and the third part by the superior mesenteric vessels in the root of the mesentery. 55 Radiological Anatomy Faculty of Applied Health Sciences Technology The duodenum curves in a C shape around the head of the pancreas. It is described as having four parts: the first (or superior), second (or descending), third (or horizontal) and fourth (or ascending). These measure approximately 2 cm, 8 cm, 8 cm and 4 cm, respectively. The first part is at the level of L1 lumbar vertebra, the second at L2, the third at L3, and the fourth ascends again to L2 level. The first part, called the duodenal cap or bulb. It is overlapped anteriorly by the liver and gallbladder. The second part of the duodenum has an opening halfway down on its posteromedial aspect for the pancreatic and common bile ducts, variously called the duodenal papilla or ampulla of Vater. This is guarded by the sphincter of Oddi. An accessory pancreatic duct (of Santorini), if present, opens 2 cm proximal to this. This part of the duodenum is crossed by the transverse mesocolon anteriorly. As a result, its upper half is supracolic and has the liver as an anterior relation. Its lower half is infracolic and has loops of jejunum anteriorly. Its posterior relations are the right kidney and adrenal gland and it is in contact with the pancreatic head medially. The third part of the duodenum curves anteriorly around L3 vertebra and the IVC and aorta. Its posterior relations also include the right psoas muscle, ureter and gonadal vessels of the posterior abdominal wall. Anteriorly it is crossed by the root of the mesentery and the superior mesenteric vessels. The fourth part of the duodenum passes upwards and to the left on the left side of the aorta, on the left psoas muscle and posterior to the stomach. Arterial supply 56 Radiological Anatomy Faculty of Applied Health Sciences Technology The first 2.5 cm of the duodenum is supplied by the right gastric and the right gastroepiploic arteries. The superior pancreaticoduodenal artery supplies from beyond this to midway along the second part. This arises from the gastroduodenal branch of the hepatic artery. The remainder of the duodenum is supplied by the inferior pancreaticoduodenal artery, the first branch of the superior mesenteric artery. At the midpoint of the second part of the duodenum, therefore, there is a transition from supply by the coeliac trunk to supply by the superior mesenteric artery, representing a transition from foregut to midgut. Venous drainage The first part of the duodenum drains to the prepyloric vein (of Mayo), which lies on the anterior surface of the pylorus. The remainder is drained by veins that correspond to the arteries and which drain to the portal and superior mesenteric veins. Lymphatic drainage Pancreaticoduodenal nodes drain to pyloric nodes and to coeliac nodes. Radiological features of the duodenum Barium studies of the duodenum The duodenum is usually examined radiologically as part of a double- contrast barium-meal examination. Because the first part of the duodenum passes posteriorly as well as superiorly, it is foreshortened in AP views. The best air-filled views are obtained with the right side raised 57 Radiological Anatomy Faculty of Applied Health Sciences Technology in a right anterior oblique view. The duodenal cap may be indented by the normal gallbladder. The cap has thin mucosal folds that are parallel, or parallel in spiral, from base to apex. The third part of the duodenum is indented by the aorta posteriorly and superior mesenteric vessels anteriorly. CT and MRI The junction of the stomach and duodenum is marked by increased thickness of the pyloric muscle posterior to the left lobe of the liver. The gastroduodenal artery may be seen posterior to the first part of the duodenum. The second part of the duodenum is seen between the liver and gallbladder laterally and the pancreatic head medially. The third part of the duodenum can always be identified passing between the superior mesenteric vessels and the aorta. The fourth part of the duodenum or the duodenojejunal flexure is visible at the L2 level. The calibre of the duodenum varies according to its position and contents: for example, the junction of second and third part may be quite redundant and distended with fluid, whereas the third part may be collapsed and attenuated as it crosses between aorta and superior mesenteric vessels. Angiography For full angiographic assessment of the duodenum, both the coeliac trunk and the superior mesenteric arteries must be visualized. THE SMALL INTESTINE The small intestine begins where the intestine assumes a mesentery at the duodenojejunal flexure and ends at the ileocaecal junction. It varies in length from 3-10 m, with an average length of 6 m. The root of its 58 Radiological Anatomy Faculty of Applied Health Sciences Technology mesentery extends from the left of L2 to the right sacroiliac joint and is only 15 cm long. The small intestine is very mobile and lies in mobile coils in the central abdomen. The proximal two-fifths of the small intestine is called the jejunum and the distal three-fifths the ileum, although the boundary between these is not well defined. The circular mucosal folds - known as valvulae conniventes or plicae semilunaris - are seen in the duodenum and continued in the small intestine, although they are less prominent distally and may be absent in distended views on barium studies. -Lymphoid follicles found in the mucous membrane throughout the intestinal tract become increasingly more numerous along the length of the small intestine. In the distal ileum they become aggregated together into patches called Peyer's patches. They are oval in shape and found on the antimesenteric border of the ileum. Arterial supply of the small intestine The entire small intestine is supplied by the superior mesenteric artery which arises from the aorta at the L1 vertebral level. Jejunal and ileal branches arise from the left of the main trunk. These branches link with one another in a series of arcades, which are usually single in the jejunum but number up to five in the distal ileum. The arteries that enter the intestinal wall - the vasa recta - are end arteries. Venous drainage of the small intestine Veins from the small intestine drain to the superior mesenteric vein, which in turn drains to the portal vein. Lymphatic drainage of the small intestine Lymph drainage is to the superior mesenteric group of preaortic nodes. 59 Radiological Anatomy Faculty of Applied Health Sciences Technology Radiological features of the small intestine Plain films of the abdomen Gas and fluid levels are often visible in normal loops of small intestine. Jejunal loops are distinguished from ileal loops by their position, with the former being in the left upper abdomen whereas the ileal loops tend to be in the lower abdomen and the right iliac fossa. Other identifying features of small-intestinal loops include the circular valvulae conniventes, as distinct from the incomplete septa formed by colonic haustra. Barium studies of the small intestine : The small intestine may be imaged using a variety of contrast techniques. In a barium follow-through examination the barium is taken orally and imaged as it passes through to the caecum. In a small-bowel enema (or enteroclysis) a tube is passed to the duodenojejunal flexure and barium is passed directly into the small intestine. appearance. Computed tomography : Oral contrast is used to distinguish normal loops of small intestine from abdominal masses. Loops of small intestine fill most of the middle abdomen and the upper pelvis. When adequately filled with oral contrast the thin wall of normal jejunum is almost imperceptible. Fine, transversely thickened areas due to the valvulae conniventes may be seen. These are seldom seen in the ileum. The mesentery and its vessels and fat may be easily seen. Lymph nodes are frequently visible in the mesentery. Angiography : 60 Radiological Anatomy Faculty of Applied Health Sciences Technology Selective injection of the superior mesenteric artery demonstrates the jejunal and ileal branches and arterial arcades. The mesenteric vessels can also be readily identified on contrast-enhanced CT and angiographic MR sequences. THE ILEOCAECAL VALVE : The distal ileum opens into the medial and posterior aspect of the large intestine at the junction of the caecum and the ascending colon. Two horizontal crescentic folds of mucosa and circular muscle project into the lumen on the colonic side. These folds are extended laterally as the frenula of the valve. Some thickening of the circular muscle of the ileum at the junction acts as a sphincter. THE APPENDIX : The appendix arises at the convergence of the taenia coli on the posteromedial wall of the caecum about 2 cm below the ileocaecal valve. It is a thin structure containing lymphoid tissue. Its length is very variable - between 12 and 24 cm long. It has its own mesentery - a triangular fold from the lower border of the ileum - and as a result is mobile. Its position is variable with the incidence of the commonest positions, as follows: Retrocaecal - 64% Inferomedial - 36% The lumen of the appendix is wide in the infant and obliterated after mid- adult life. Acute appendicitis, which is usually caused by obstruction of the lumen, is therefore rare in the extremes of life. 61 Radiological Anatomy Faculty of Applied Health Sciences Technology The appendix is supplied by the appendicular artery which reaches it in the mesoappendix from the ileocolic artery. This is its sole supply. Lymph drainage is to the paracolic nodes along the ileocolic artery to the SMA group. Radiological features of the appendix Plain abdominal film Faecoliths or fluid levels of the appendix may be visible on plain films of the abdomen in the right iliac fossa in approximately 10% of individuals. Barium enema : If the lumen of the appendix is patent, it may fill on barium enema examination. The lumen is often obliterated in patients past mid- adulthood. To fill the appendix the patient should be supine because its orifice is on the posterior aspect of the caecum. Some elevation of the head is also helpful. CT and MRI The normal appendix can usually be identified arising from the caecum inferior to the insertion of the terminal ileum. THE LARGE INTESTINE : The length of the large intestine is very variable, with an average length of 1.5 m. It is wider in diameter than the small intestine, with a maximum diameter of the caecum at 9 cm and the transverse colon at 5.5 cm. 62 Radiological Anatomy Faculty of Applied Health Sciences Technology As far as the rectum the colon is marked by taeniae coli. These are three flattened bands of longitudinal muscle that represent the longitudinal muscle layer of the colon. The taeniae converge on the appendix proximally and the rectum distally, and these structures have a complete longitudinal muscle layer. The taeniae coli are about 30 cm shorter than the colon and cause the formation of sacculations along its length. On radiographs these give rise to the appearance of incomplete septa, called haustra. Scattered over the free surface of the large intestine, except for the caecum and rectum, are fat-filled peritoneal tags called appendices epiploicae. These are especially numerous in the sigmoid colon. Arteries supplying these perforate the muscle wall. The caecum is a blind pouch of large bowel proximal to the ileocaecal valve. It is approximately 6 cm long and usually has its own mesentery, making it mobile and easily distensible. The ascending colon runs from the ileocaecal valve to the inferior surface of the liver, where it turns medially into the hepatic flexure. The transverse colon runs from the hepatic flexure across the midline to the splenic flexure. The descending colon runs from the splenic flexure inferiorly to the sigmoid colon. Peritoneal attachments of the colon : 63 Radiological Anatomy Faculty of Applied Health Sciences Technology The ascending and descending parts of the colon are usually retroperitoneal (covered anteriorly and on both sides by peritoneum). The peritoneal spaces lateral to these are called the paracolic gutters. Occasionally the ascending colon has a mesentery. The caecum does not have a mesentery, but is completely invested in peritoneum and is relatively mobile. The transverse colon, however, always has a mesentery, the mesocolon, on which it hangs in a loop between the hepatic and splenic flexures, which are fixed points. The splenic flexure is attached to the diaphragm by the phrenicocolic ligament. The convexity of the greater curve of the stomach lies in the concavity of the loop of transverse colon. The gastrocolic ligament attaches the stomach and transverse colon. This continues below the transverse colon as the greater omentum. The sigmoid colon also has a mesentery. This is attached to the posterior abdominal wall to the left of the midline in an inverted V shape whose limbs diverge from the bifurcation of the common iliac artery over the sacroiliac (SI) joint at the pelvic brim. The rectum has peritoneum anteriorly and laterally in its upper third and anteriorly only in its middle third. The lower third of the rectum is below the pelvic peritoneum. The arterial supply of the colon : That part of the colon derived from the midgut (i.e. to the midtransverse colon) is supplied by the superior mesenteric artery as follows: The ileocolic artery (a continuation of the main trunk of the superior mesenteric artery) supplies the caecum, appendix and the beginning of the ascending colon. The right colic artery supplies the remainder of the ascending colon. 64 Radiological Anatomy Faculty of Applied Health Sciences Technology The middle colic artery supplies the transverse colon to its midpoint. The inferior mesenteric artery supplies the colon as far as the upper rectum as follows: The left colic artery to the descending colon; The sigmoid artery to the sigmoid colon; and The superior rectal (superior haemorrhoidal) artery to the upper rectum. Each of these vessels anastomoses with its neighbor forming a marginal artery (of Drummond) close to the colon. The vessels that enter the bowel are, however, end arteries. Venous drainage of the colon Veins corresponding with the arteries drain to the superior and inferior mesenteric veins. Lymphatic drainage of the colon Lymph drains to nodes near the bowel wall, which drain to nodes in the mesentery and retroperitoneum along with the mesenteric vessels. The drainage of the right colon to midtransverse colon is with the superior mesenteric vessels to the peripancreatic nodes and superior mesenteric group of para-aortic nodes. The drainage of the left side of transverse and left colon is along the inferior mesenteric vessels to the inferior mesenteric nodes at the origin of the inferior mesenteric artery at the level of the third lumbar vertebra. Radiological features of the colon Plain films of the abdomen Gas within the colon outlines the colon or parts of it. The sacculation of the colon by the taeniae coli gives rise to septa called haustra. The haustra are fixed anatomical structures in the proximal 65 Radiological Anatomy Faculty of Applied Health Sciences Technology colon, but in the distal colon require active contraction for their formation. Haustra may be absent distal to the midtransverse colon. Double-contrast barium-enema examination : The entire colon and appendix may be outlined. The technique for filling the colon with barium and air requires an understanding of anatomy. Because the transverse colon, for example, hangs anteriorly between the relatively posteriorly positioned splenic and hepatic flexures, this is easiest to fill when the patient is prone. Resumption of a supine position allows filling of the hepatic flexure and the ascending colon with barium. The junction of the caec

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