Radiologic Correlation of Brain Anatomy PDF

Imaging of the Brain and Spinal cord Ronnie Dan G. Salazar, MD Learning Objectives: Discuss the different Radiologic imaging modalities for the brain and spinal cord Identify different anatomical structures that are commonly seen Identify common pathologic condition that can be...

Imaging of the Brain and Spinal cord Ronnie Dan G. Salazar, MD Learning Objectives: Discuss the different Radiologic imaging modalities for the brain and spinal cord Identify different anatomical structures that are commonly seen Identify common pathologic condition that can be identified through imaging. Diagnostic Imaging Modalities for the Head and Spinal cord 1.Cranial Ultrasound 2.Xray 3.Cranial and spine Ct scan (Computed Tomography) 4.Cranial and spine MRI (Magnetic resonance imaging)  CT (CT abdo used as X-ray (CXR used as Factor MRI Ultrasound example) example) 5-10 Duration 3-7 minutes 30-45 min 2-3 min minutes Cost Cheaper Expensive Cheap Cheap Dimensions 3 3 2 2 Excellent Soft tissue Poor detail Poor detail Poor detail detail Bone Excellent detail Poor detail Excellent detail Poor detail Radiation 10mSv None 0.15mSv None Cranial ultrasound(CUS) Uses sound waves to produce pictures of the brain and cerebrospinal fluid. An extremely valuable tool for the evaluation of the brain during the first year of life. It is the initial screening imaging tool to evaluate the infants’ brain and complementary to the use of computed tomography (CT) and magnetic resonance imaging (MRI). Advantages It is safe (lack of ionizing radiation, no need for sedation), Inexpensive, Portable Can be quickly performed, and repeated as many times as necessary.  Indications of CUS in neonates and infants Abnormal increase in head circumference; Haemorrhage or parenchymal abnormalities in preterm and term infants; Ventriculomegaly/hydrocephalus; Vascular abnormalities; Suspected hypoxic ischemic injury; Patients on hypothermia, extracorporeal membrane oxygenation (ECMO), and other support machines; Congenital malformations; Signs or symptoms of a central nervous system disorder (e.g., seizures, facial malformations, macrocephaly, microcephaly, and intrauterine growth restriction); Congenital or acquired brain infection; Suspected or known head trauma; Craniosynostosis; Follow-up or surveillance of previously documented abnormalities, including prenatal abnormalities; Screening before surgery.  NORMAL ULTRASOUND ANATOMY. Normal sagittal at the Normal anterior coronal 3rd and 4th ventricles. neonatal brain. Neonatal brain normal parasagittal Normal parasagittal at the Normal mid-anterior coronal at the lateral ventricles. sylvian fissures and 3rd ventricle.  Normal mid coronal view at Normal far-posterior coronal. the level of the brain stem  Normal coronal view of the lateral The level of the trigone of the lateral venticles, ventricles and caudao-thalamic groove. visualizing the body of the choroid plexii.  The superior sagittal sinus and other vascular Normal far-posterior coronal. channels can be readily assessed with power Doppler.  Xrays An X-ray image, also known as a radiograph, XR, or Xray, is a type of medical imaging that uses electromagnetic radiation in the form of X-rays to produce images of internal structures of the body. X-rays penetrate through the body, and different densities of tissue, such as bones and organs, absorb different amounts of the X-rays, creating an image on a film or digital detector. A radiological investigation of the skull vault and associated bony structures. Plain radiography of the skull is often the last resort in trauma imaging in the absence of a CT How do X-rays work? An X-ray machine produces a beam of X-rays, which are a form of ionizing radiation, by accelerating electrons through a high voltage. The electrons collide with a metal target, releasing X-rays in the process. The X-rays penetrate through the body and pass through different tissues at different rates. Dense tissues such as bones absorb more X-rays and appear white on the resulting image, while less dense tissues such as muscles and organs absorb fewer X-rays and appear darker. An X-ray film or digital detector is placed on the other side of the body from the X-ray source. The X-rays that pass through the body are recorded on the film or digital detector, creating a black and white image of the internal structures. Indications X-rays of the skull may be done to diagnose: Fractures of the bones of the skull, Decalcification of the bone, Birth defects, Infection, Pituitary tumors, Certain metabolic and endocrine disorders that cause bone defects of the skull. Magnified technique to evaluate palpable bony lesions on the scalp To exclude the presence of metallic foreign bodies contraindicated to MRI Skull Radiographic Anatomy. Skull - PA 0 Degree Angulation. PA 15 Degree Angulation (Caldwell). Adult Skull - Townes View Adult Skull - Lateral View Fracture Depressed skull fracture Which spine conditions can be diagnosed using X-ray? Fractures or dislocations: Degenerative disorders: X-rays can help diagnose conditions such as osteoarthritis Scoliosis: X-rays can be used to diagnose scoliosis Spine Benefits of X-ray 1.Cost: X-rays are often less expensive than MRI or CT scans. 2.Availability: X-ray machines are widely available and typically faster to use. 3.Low radiation exposure: X-rays use low levels of ionizing radiation, which is generally considered safe for diagnostic purposes. CT scans, on the other hand, use higher levels of radiation. 4.Real-time imaging: Some types of X-ray machines can produce images in real-time. 5.Portability: X-rays can be performed at the bedside in a hospital or clinic. Limitations of X-ray 1.Limited soft tissue detail: X-rays best produce images of bone and do not provide detailed images of soft tissues, such as muscles, nerves, and ligaments. 2.Limited views: X-rays typically only produce images from one or two angles, making it difficult to fully evaluate complex conditions or structures. 3.Radiation exposure: X-rays use ionizing radiation, which can increase the risk of cancer with repeated exposure. Is X-ray safe? Philippine Dose Registry (PhilDose) Personal doses are reported in terms of personal dose equivalent: Hp(10) for the whole body dose, Hp(0.07) for skin dose. They are presented in units of milli-Sievert (mSv) which is characterized by the amount of biological damage a radiation does to the tissue. The current dose limits as per national regulations are as follows: (a) An effective dose of 20 mSv per year averaged over five consecutive years; (b) An effective dose of 50 mSv in any single year; (c) An equivalent dose to the lens of the eye of 150 mSv in a year; and (d) An equivalent dose to the extremities (hands and feet) or the skin of 500 mSv in a year. The amount of radiation: one adult chest x-ray (0.1 mSv) = 10 days of natural background radiation that we are all exposed to as part of our daily living. BONE Procedure Approximate effective Comparable to natural radiation dose background radiation for: Lumbar Spine 1.4 mSv 6 months Extremity (hand, foot, etc.) Less than 0.001 mSv Less than 3 hours X-ray CT scan Basic Physics of CT CT scanning  Hounsfield Unit Measurements Bone ~ +613 HU White Matter ~ +24.7 HU Gray Matter ~ +35.8 HU CSF - Ventricle ~ +3.3 HU Scalp Fat ~ -84.5 HU Air ~ -966.3 HU Tissue Density Differences Lower density substances allow more photons pass through to the detectors, resulting in a grayer or blacker appearance on CT – like CSF The X-ray beam is attenuated to a higher degree by calcium, therefore less photons pass through bone to the detectors, resulting in its ‘white’ appearance on CT White matter is less cellular, contains myelinated axons (fat), and has a higher water content than gray matter, resulting in slightly lower attenuation values or density. The brightness of the image is adjusted via the window level. The contrast is adjusted via the window width. Different Window Level Brain Window – shows subarachnoid hemorrhage (blood proteins/clot) is high density in the basilar cisterns with small foci of air (red arrows) related to trauma Soft Tissue Window – shows scalp hematoma Bone window – shows bullet fragment and fracture CT Neuroimaging The head is routinely scanned using sequential imaging in the axial plane with each section measuring 5 mm thick Helical imaging is used for CT angiograms of the head/neck and other parts of the body Head CT Approach First - evaluate normal anatomical structures, window for optimal brain tissue contrast Second – assess for signs of underlying pathology such as: mass effect, edema, midline shift, hemorrhage, hydrocephalus, subdural or epidural collection/hematoma, or infarction Third – evaluate sinuses and osseous structures with bone windows Fourth – use a soft tissue window to assess extracranial anatomy – orbits, face, scalp  CT brain anatomy Skull bones and sutures The brain is located inside the cranial vault, a space formed by bones of the skull and skull base. Everything inside the cranial vault is 'intra-cranial' and everything outside is 'extra- cranial'. Skull bones Bones of the skull and skull base - frontal, parietal, occipital, ethmoid, sphenoid and temporal bones - all ossify separately and gradually become united at the skull sutures. The skull has inner and outer tables of cortical bone with central cancellous bone called 'dipole. Skull bone structure - CT brain - (bone windows) Sutures The main sutures of the skull are the coronal, sagittal, lambdoid and squamosal sutures. The metopic suture (or frontal suture) is variably present in adults. Coronal suture - unites the frontal bone with the parietal bones Sagittal suture - unites the 2 parietal bones in the midline Lambdoid suture - unites the parietal bones with the occipital bone Squamosal suture - unites the squamous portion of the temporal bone with the parietal bones Metopic suture - (if present) unites the 2 fontal bones Skull bones and sutures - (superior view). Coronal suture (BLUE). Lambdoid suture (GREEN). Squamosal suture (RED). Sagittal suture (PURPLE). Metopic suture (ORANGE) - variably present in adults. Cranial fossae - CT brain - (bone windows) Anterior cranial fossa - accommodates the anterior part of the frontal lobes Middle cranial fossae - accommodate the temporal lobes Posterior cranial fossa - accommodates the cerebellum and brain stem Pituitary fossa (PF) - accommodates the pituitary gland Meninges The meninges are thin layers of tissue found between the brain and the inner table of the skull. The meninges comprise the dura mater, the arachnoid, and the pia mater. The dura mater and arachnoid are an anatomical unit, only separated by pathological processes. The falx cerebri and the tentorium cerebelli are thick infoldings of the meninges which are visible on CT imaging. Elsewhere the meningeal layers are not visible on CT as they are closely applied to the inner table of the skull. Tentorium cerebelli The tentorium cerebelli - an infolding of the dura mater - forms a tent-like sheet which separates the cerebrum (brain) from the cerebellum The tentorium is anchored by the petrous bones Tentorium cerebelli On axial slice CT images of the brain the tentorium is faintly visible passing over the cerebellum Tentorium cerebelli - clinical significance In the context of subarachnoid hemorrhage or subdural hematoma the tent may become more dense due to layering of blood. Falx cerebri The falx is an infolding of the meninges which lies in the midline and separates the left and right cerebral hemispheres Falx cerebri - clinical significance Pathological processes may cause 'mass effect' with deviation of the falx towards one side Falx and tentorium Coronal slice CT images show that the tentorium cerebelli is continuous with the falx cerebri. Falx and tentorium - clinical significance Meningiomas are benign intracranial tumours which may arise from any part of the meninges, including the falx or tentorium. CSF spaces The brain is surrounded by cerebrospinal fluid (CSF) within the sulci, fissures and basal cisterns. CSF is also found centrally within the ventricles. The sulci, fissures, basal cisterns and ventricles together form the 'CSF spaces', also known as the 'extra-axial spaces'. CSF is of lower density than the grey or white matter of the brain, and therefore appears darker on CT images. An appreciation of the normal appearances of the CSF spaces is required to allow assessment of brain volume. Sulci The brain surface is formed by folds of the cerebral cortex known as gyri. Between these gyri there are furrows, known as sulci, which contain CSF. Sulci and gyri Gyrus = a fold of the brain surface (plural = gyri) Sulcus = furrow between the gyri which contains CSF (plural = sulci)  Fissures. The fissures are large CSF-filled clefts which separate structures of the brain. Fissures. The interhemispheric fissure separates the cerebral hemispheres - the two halves of the brain The Sylvian fissures separate the frontal and temporal lobes. Ventricles The ventricles are spaces located deep inside the brain which contain CSF. Lateral ventricles The paired lateral ventricles are located on either side of the brain The lateral ventricles contain the choroid plexus which produces CSF. Note : The choroid plexus is almost always calcified in adults. Third ventricle The third ventricle is located centrally The lateral ventricles communicate with the third ventricle via small holes (foramina of Monro). Fourth ventricle The fourth ventricle is located in the posterior fossa between the brain stem and cerebellum It communicates with the third ventricle above via a very narrow canal, the aqueduct of Sylvius (not shown). Basal cisterns CSF in the basal cisterns surrounds the brain stem structures. Brain parenchyma and lobes The brain consists of grey and white matter structures which are differentiated on CT by differences in density. White matter has a high content of myelinated axons. Grey matter contains relatively few axons and a higher number of cell bodies. As myelin is a fatty substance it is of relatively low density compared to the cellular grey matter. White matter, therefore, appears blacker than grey matter. Key points Grey matter appears grey White matter appears blacker Grey matter v white matter White matter is located centrally and appears blacker than grey matter due to its relatively low density. Clinical significance Pathological processes may increase or decrease the differentiation in density between grey and white matter. Brain lobes The brain has paired, bilateral anatomical areas or 'lobes'. These do not exactly correlate with the overlying bones of the same names. Brain lobes - CT brain (superior slice) On both sides the frontal lobes are separated from the parietal lobes by the central sulcus (arrowheads) Note: The frontal lobes are large and the parietal and occipital lobes are relatively small Brain lobes - CT brain (inferior slice) The most anterior parts of the frontal lobes occupy the anterior cranial fossae The temporal lobes occupy the middle cranial fossae The cerebellum and brain stem occupy the posterior fossa Lobes v 'regions' CT does not clearly show the anatomical borders of the lobes of the brain. For this reason radiologists often refer to 'regions', such as the 'parietal region' or 'temporal region', rather than lobes. If more than one adjacent region needs to be described then conjoined terms can be used such as 'temporo-parietal region' or 'parieto-occipital region' Lobes v 'regions' The parietal lobe is not clearly delineated from the temporal or occipital region Grey matter structures Important grey matter structures visible on CT images of the brain include the cortex, insula, basal ganglia, and thalamus. Cortical grey matter The grey matter of the cerebral cortex is formed in folds called gyri Note that the cortex appears whiter (denser) than the underlying white matter. Insula The insula forms an inner surface of the cerebral cortex found deep to the Sylvian fissure. Insula - clinical significance Loss of definition of the insular cortex may be an early sign of an acute infarct involving the middle cerebral artery territory. Basal ganglia and thalamus The thalamus and the basal ganglia are readily identifiable with CT Basal ganglia = lentiform nucleus + caudate nucleus Basal ganglia - clinical significance Insults to the basal ganglia may result in disorders of movement. Thalamus - clinical significance Insults to the thalamus may result in thalamic pain syndrome. White matter structures White matter of the brain lies deep to the cortical grey matter. The internal capsules are white matter tracts which connect with the corona radiata and white matter of the cerebral hemispheres superiorly, and with the brain stem inferiorly. The corpus callosum is a white matter tract located in the midline. It arches over the lateral ventricles and connects white matter of the left and right cerebral hemispheres. Key points The internal capsules and corpus callosum are clinically important white matter tracts. Corpus callosum - CT brain - sagittal image Sagittal CT images show the corpus callosum as a midline structure arching from anterior to posterior Posterior fossa The posterior fossa accommodates the cerebellum and brain stem. Superiorly the cerebellum is separated from the cerebral hemispheres by the tentorium cerebelli. Posterior fossa The brain stem and cerebellum occupy the posterior fossa  Cerebral vascular territories Different areas of the brain are supplied by the anterior, middle and posterior cerebral arteries in a predictable distribution. The posterior fossa structures are supplied by the vertebrobasilar arteries. The arteries of the brain are not well visualized on conventional CT, but a knowledge of the areas of the brain they supply is helpful in determining the source of a vascular insult. Key points The cerebral and vertebrobasilar arteries supply regions of the brain in a predictable distribution. Vascular territories - (above lateral ventricles) The anterior cerebral arteries supply a narrow band of the cerebral hemispheres adjacent to the midline. The middle cerebral artery supplies the largest area of the brain. Vascular territories - (at level of insula) Multiple tiny perforating branches of the middle cerebral artery supply the region of the basal ganglia and insula Vascular territories – at level of cerebellum The vertebrobasilar arteries supply the cerebellum and brain stem Calcified structures There are several structures in the brain which are considered normal if calcified. Knowledge of these structures helps avoid confusion, especially when considering if there is intracranial hemorrhage present. The commonly calcified structures include the choroid plexus, the pineal gland, the basal ganglia, and the falx. Key points Commonly calcified structures of the brain include the choroid plexus, pineal gland, basal ganglia and falx Use of CT 'bone windows' is helpful in differentiating calcified structures from acute hemorrhage. Calcified choroid plexus In adults the choroid plexus of the lateral ventricles is almost always calcified. Calcified pineal gland The pineal gland is located immediately posterior to the third ventricle. It is very commonly partly or fully calcified in adults. Calcified basal ganglia Calcification of the basal ganglia is common in elderly patients. Calcified falx cerebri The falx is commonly calcified in adults If viewed on brain windows only, calcification of the falx can be mistaken for acute intracranial blood Use of CT 'bone windows' show calcification of the falx more clearly. Axial CT images from skull base up to the vertex. Sinuses in the Axial Plane Left to right: frontal sinus, ethmoid sinus, maxillary sinus and sphenoid sinus CT Angiographic Anatomy Red – MCA or middle cerebral artery Yellow – ACA Green – PCA Blue – Basilar artery  Red – anterior cerebral arteries Yellow – vein of Galen Purple – superior sagittal sinus Green – straight sinus Blue – basilar artery Trauma Acute hemorrhage is bright on CT, due to increased attenuation of the X-ray photons by blood proteins as clot forms In this case, there is subarachnoid and intraventricular hemorrhage Subdural Hematoma Epidural Hematoma  Effective Radiation dose in adults CENTRAL NERVOUS Procedure Approximate effective Comparable to natural SYSTEM radiation dose background radiation for: Computed Tomography 1.6 mSv 7 months (CT)–Brain Computed Tomography (CT)–Brain, repeated 3.2 mSv 13 months with and without contrast material Computed Tomography 1.2 mSv 5 Months (CT)–Head and Neck Computed Tomography 8.8 mSv 3 years (CT)–Spine MRI Magnetic Resonance Imaging (MRI) is a medical imaging technique that uses a magnetic field and computer- generated radio waves to create detailed images of the organs and tissues in the body The strong magnetic field created by the MRI scanner causes the atoms in the body to align in the same direction. Radio waves are then sent from the MRI machine and move these atoms out of the original position. As the radio waves are turned off, the atoms return to their original position and send back radio signals. These signals are received by a computer and converted into an image of the part of the body being examined. This image appears on a viewing monitor.  Since it is clear that an MRI image is made after interaction between a specific tissue and an MRI machine that uses some kind of physical mechanisms.  When it comes to the tissue properties, it is all about protons. It is known that protons behave like magnet bars, which means they have one positive and one negative pole, and that makes them responsive to external magnetic fields. And since the human body consists mostly of water and fat molecules, that gives it a huge amount of hydrogen (H+) as a source of protons that is needed for interaction with specific radio-waves of the MRI scanner. So, in this manner of speaking, our body composition actually makes the MRI capable of mapping the location of water and fat in the body. Each proton spins around its axis, like a ballerina doing a pirouette. While it spins, it constantly changes the ''phase''. When hydrogen protons are exposed to a strong magnetic field, such as the one of the MRI scanner, most of them will align with that field. MRI hits protons with a radio wave pulse that gives them the energy to start rotating in the clockwise direction until full 180 degree rotation, when they realign with the magnetic field but in the opposite direction. once it is turned off, protons relax and realign with the external magnetic field once again, releasing electromagnetic energy along the way.  MRI facts: Basis Creation of 2D and 3D images by distinguishing between the nuclear magnetic properties of various tissues Energy Magnetic fields, radio waves T1 Weighted Images High signal for fat, high signal for contrast substances (Gadolinium), low signal for water T2 Weighted Images Low signal for fat, low signal for contrast substances, high signal for water Fluid Attenuated Inversion Similar to T1 weighted images Recovery Proton Density High signal for fat but lower than in T1, intermediate signal for water but lower than T2 Scanner Types Open, closed Contraindications Metal implants, pregnancy, allergies to contrast substances, kidney disease Advantages Safe (no ionizing radiation), excellent ability for soft tissue differentiation, multiplanar imaging, image quality not degraded by bone or air Brain Normal MR Anatomy. Sagittal Images. Circle of Willis A1-segment Anterior cerebral artery from carotid bifurcation to anterior communicating artery gives rise to the medial lenticulostriate arteries. A2-segment Part of anterior cerebral artery distal to the anterior communicating artery. P1-segment Part of the posterior cerebral artery proximal to the posterior communicating artery. The posterior communicating artery is between the carotid bifurcation and the posterior cerebral artery) P2-segment Part of the posterior cerebral artery distal to the posterior communicating artery M1-segment Horizontal part of the middle cerebral artery which gives rise to the lateral lenticulostriate arteries which supply most of the basal ganglia. The M2-segment is the part in the sylvian fissure and the M3-segment is the cortical segment. Cisterna ambient Also called ambient cistern is a cistern of the subarachnoid space between the posterior end of the corpus callosum and the superior surface of the cerebellum. It is sometimes defined as including the quadrigeminal cistern. Horizontal M1-segment gives rise to the lateral lenticulostriate arteries which supply part of head and body of caudate, globus pallidus, putamen and the posterior limb of the internal capsule. Notice that the medial lenticulostriate arteries arise from the A1-segment of the anterior cerebral artery. Sylvian M2-segment Branches supply the temporal lobe and insular cortex (sensory language area of Wernicke), parietal lobe (sensory cortical areas) and inferolateral frontal lobe Cortical M3-segment Branches supply the lateral cerebral cortex Anterior commissure The anterior commissure is a bundle of white fibers that connects the two cerebral hemispheres across the middle line. At this level frequently perivascular CSF-spaces of Virchow-Robin are seen. Thalamic level. Hippocampus Spine Herniated Disc  References: 1. RadiologyInfo.org 2.SpineInfo: Xrays: how it works, strength and limitations by Dave Harrison, MD 3.Philippine Nuclear Research Institute, radiation protection. 4.BASIC APPROACH TO HEAD CT INTERPRETATION, David Zimmerman, M.D. 5.MRI: The basics: Jana Vasković MD , Dimitrios Mytilinaios MD, PhD November 03, 2023 Food for thought: Matthew 6:33 KJV: But seek ye first the kingdom of God, and his righteousness; and all these things shall be added unto you. Thank You