Brain & Skull PDF

COURSE UNIT 1 SECTIONAL ANATOMY & PATHOLOGY BRAIN AND SKULL CONTENTS: 1. Basic sectional and radiographic anatomy ◦ Image orientation ◦ Skull and bones ◦ Sinuses ◦ Meninges ◦ CSF spaces ◦ Brain parenchyma and lobes ◦ Grey and white matter structures ◦ Post...

COURSE UNIT 1 SECTIONAL ANATOMY & PATHOLOGY BRAIN AND SKULL CONTENTS: 1. Basic sectional and radiographic anatomy ◦ Image orientation ◦ Skull and bones ◦ Sinuses ◦ Meninges ◦ CSF spaces ◦ Brain parenchyma and lobes ◦ Grey and white matter structures ◦ Posterior fossa and brain stem 2. Traumatic brain injury -intracranial haemorrhage Extra-axial haemorrhage : extradural haemorrhage subdural haemorrhage subarachnoid haemorrhage Intra-axial haemorrhage -Sequelae and complications : mass effect, cerebral edema, herniation Skull fractures 3. Non traumatic emergency brain condition: Hydrocephalus- Infection-Meningitis, encephalitis, abscess, empyema Acute ischemic stroke Hypoxic ischemic encephalopathy PART I RADIOGRAPHIC ANATOMY AND IMAGE ORIENTATION SKULL Anatomy ◦ The skull consists of 8 cranial bones and 14 facial bones. ◦ Cranial bones divided into calvaria and floor ◦ Calvaria: Frontal, right parietal, left parietal and occipital ◦ Floor: Right temporal, left temporal, sphenoid, ethmoid. ◦ 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 ◦ Vascular impression -appears grey -has branches that gradually decrease in size peripherally. -has well defined sclerotic margin  Distinguishing fracture Vascular marking Fracture Appears grey Frequently appears black Has branches that gradually Has branches that do not taper decrease in size peripherally Has well defined sclerotic margin Does not have a well defined white margin Lateral skull radiograph AP skull radiograph  SECTIONAL ANATOMY AND IMAGE ORIENTATION Skull and bone Sinuses Meninges CSF spaces Brain parenchyma and lobes Grey and white matter structures Posterior fossa and brain stem Skull and bones ◦ 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'. ◦ Main skull bones - frontal, parietal, occipital, ethmoid, sphenoid and squamous temporal ◦ Main sutures - coronal, sagittal, lambdoid and squamosal ◦ CRANIAL FOSSAE ◦ 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 - accommodates the pituitary gland  Sinuses ◦ The skull contains air sinuses which are highly variable in appearance between different individuals ◦ Maxillary sinuses are important in orbital injury ◦ The sphenoid sinus and ethmoid air cells are continuous with the nasal airways. Both are important in basal skull fracture ◦ The mastoid air cells are continuous with the middle ear ◦ The frontal sinuses are highly variable in appearance ◦ Some people have no frontal sinuses SPHENOID SINUSES Meninges ◦ The brain is protected (from the outer to the inner layer) by the skull, meninges, and cerebrospinal fluid (CSF). ◦ The meninges are organized into ◦ dura mater, ◦ arachnoid membrane, ◦ pia ◦ These coverings have two major functions: -Provide a supportive framework for the cerebral and cranial vasculature. -Acting with cerebrospinal fluid to protect the CNS from mechanical damage. ◦ The meninges are often involved cerebral pathology, as a common site of infection(meningitis), and intracranial bleeds Dura Mater ◦ The dura mater is the outermost layer of the meninges and is located directly underneath the bones of the skull and vertebral column. ◦ It is thick, tough, and inextensible. ◦ The dural venous sinuses are located between the two layers of dura mater. They are responsible for the venous drainage of the cranium and empty into the internal jugular veins. DURAL REFLECTION ◦ The meningeal layer of dura mater folds inwards upon itself to form four dural reflections. ◦ The four dural reflections are: ◦ Falx cerebri – projects downwards to separate the right and left cerebral hemispheres. ◦ Tentorium cerebelli – separates the occipital lobes from the cerebellum. It contains a space anteromedially for passage of the midbrain – the tentorial notch. ◦ Falx cerebelli – separates the right and left cerebellar hemispheres. ◦ Diaphagma sellae – covers the hypophysial fossa of the sphenoid bone. It contains a small opening for passage of the stalk of the pituitary gland Arachnoid mater ◦ The arachnoid mater is the middle layer of the meninges, lying directly underneath the dura mater. ◦ It consists of layers of connective tissue, is avascular, and does not receive any innervation. ◦ Underneath the arachnoid is a space known as the sub- arachnoid space. It contains cerebrospinal fluid, which acts to cushion the brain. Small projections of arachnoid mater into the dura (known as arachnoid granulations) allow CSF to re-enter the circulation via the dural venous sinuses. Pia mater ◦ The pia mater is located underneath the sub-arachnoid space. It is very thin, and tightly adhered to the surface of the brain and spinal cord. It is the only covering to follow the contours of the brain (the gyri and fissures). ◦ Like the dura mater, it is highly vascularised, with blood vessels perforating through the membrane to supply the underlying neural tissue. Ventricles ◦ 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. 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. Brain lobes - CT brain (superior slice) Brain lobes- CT scan ( inferior slice) Grey matter structures ◦ Important grey matter structures visible on CT images of the brain include the cortex, insula, basal ganglia, and thalamus. ◦ The grey matter of the cerebral cortex is formed in folds called gyri ◦ The cortex appears whiter (denser) than the underlying white matter ◦ The insula forms an inner surface of the cerebral cortex found deep to the Sylvian fissure ◦ Basal ganglia and thalamus are important grey matter structures which are located deep to the insula. White matter structures ◦ White matter of the brain lies deep to the cortical grey matter. ◦ 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. ◦ 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 Posterior cranial fossa ◦ The posterior cranial fossa is comprised of three bones: the occipital bone and the two temporal bones. ◦ The posterior cranial fossa accommodates the cerebellum and brain stem. ◦ Superiorly the cerebellum is separated from the cerebral hemispheres by the tentorium cerebelli. CEREBRAL VASCULAR TERITORRIES ◦ intracranial circulation can be conveniently divided into anterior and posterior circulation, on the basis of internal carotid arteries and vertebral arteries supply respectively. ◦ anterior circulation ◦ Anterior choroidal artery ◦ Anterior cerebral artery ( ACA ) ◦ Middle cerebral artery (MCA) ◦ posterior circulation ◦ Posterior cerebral artery ( PCA ) ◦ Basilar artery ◦ The arteries of the brain are not well visualised on conventional CT, but a knowledge of the areas of the brain they supply is helpful in determining the source of a vascular insult. ◦ 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 ◦ The vertebrobasilar arteries supply the cerebellum and brain stem ABOVE LATERAL VENTRICLE LEVEL OF INSULA LEVEL OF CEREBELLUM PART II Traumatic Brain Injury ◦ Intracranial haemorrhage 1. Extra-axial haemorrhage : ◦ extradural haemorrhage ◦ subdural haemorrhage ◦ subarachnoid haemorrhage 2.Intra-axial haemorrhage ◦ -Sequelae and complications : mass effect, cerebral edema, herniation ◦ Skull fractures Extraaxial Haemorrhages ◦extradural haemorrhage ◦subdural haemorrhage ◦subarachnoid haemorrhage Extradural/epidural haemorrhage ◦ bleeding in the virtual space between the dura mater and the skull. ◦ Resulting from injury to an intracranial artery, most commonly the middle meningeal artery. ◦ Leakage from an injured artery results in collection of blood which strips the dura mater away from the inner table of the skull. ◦ lens-shaped haematoma collection. ◦ an epidural hematoma can cross the midline because it is located between the dura and the skull. ◦ However since the dura is tightly adherent to the adjacent skull near suture lines, an epidural hematoma usually does not cross suture lines. Subdural haemorrhage ◦ A collection of blood between the inner layer of the dura and the arachnoid. ◦ It cannot cross the midline, but can be located near dural folds like the falx or the tentorium. ◦ Cresent-shaped collection - A subdural collection is not limited by the attachment points of the dura to bone, thus it can cross suture ◦ It usually results from rupture of the cortical bridging veins. It usually occurs in head trauma and especially in patients who are treated with anticoagulants. ◦ It is most common in elderly and alcoholics with atrophy. In brain atrophy the venous subdural structures are less well “packed” against the skull, which give them more space to move and possibility to torn. ◦ Subdural haematomas may be bilateral - as in this image ◦ The low density material in these subdural collections is due to a chronic subdural haematoma ◦ The higher density layered material is due to more recent haemorrhage Subarachnoid haemorrhage ◦ Resulting from disruption of small subarachnoid vessels or direct extension into subarachnoid space by contusion or haematoma. ◦ Linear areas with high attenuation within cisterns or sulci. ◦ Larger areas of subrachnoid haemorrhage with unconscious patient may indicate ruptures aneurysm Intra-axial/intracerebral haemorrhage ◦ Could be either traumatic or spontaneous ( high BP) ◦ May be associated with cortical contusion or ruptures of small intraparenchymal blood vessels. ◦ In trauma setting, may or may not be associated with skull fractures ◦ May associated with extra axial haemorrhage Traumatic Brain Injury: Sequelae and complications ◦ Mass effect ◦ Cerebral edema ◦ Herniation MASS EFFECT ◦ Skull is fixed volume and cannot increased in size ◦ A lesion in the skull any displaces or compresses adjacent structures ◦ Eg: haemorrhage ◦ tumour ◦ huge infarct ◦ cerebral abscess ◦ Stages of mass effect: ◦ Effacement of the sulci adjacent to the lesion ◦ partial or complete effacement of the adjacent ventricles. ◦ Effacement of the sulci and ventricles may extend across the whole hemisphere. ◦ displacement of midline structures, and then effacement of the contralateral ventricles and sulci. ◦ herniation of structures through the incisura tentorii or coning (extrusion of the posterior fossa structures through the foramen magnum). These uncommon features are associated with extremely poor outcome. ◦ A large acute left subdural haematoma is causing severe mass effect ◦ The left hemisphere sulci and lateral ventricle are effaced ◦ The midline structures are shifted to the right ◦ The contralateral sulci are effaced ◦ The right lateral ventricle is distorted - effaced anterior horn and focal hydrocephalus of the posterior horn ◦ A small intracerebral bleed with surrounding oedema ◦ Combination of the blood and oedema is causing mass effect: effacement of the adjacent sulci and partial effacement of the adjacent lateral ventricle ◦ Left hemisphere structures appear normal CEREBRAL EDEMA Collection of abnormal fluid within the white matter of the brain Poor grey white matter differentiation Cerebral sulci effacement  HERNIATION -Shift of brain tissue from its normal location, into adjacent space as a result of mass effect Life threatening, need prompt diagnosis SKULL FRACTURES ◦ Brain and bone windows on every trauma cases ◦ Skull sutures are jagged ◦ Acute skull fractures are straight and are not corticated Sutures VS Fractures PART III Non traumatic emergency brain condition: Hydrocephalus Infection-Meningitis, encephalitis, abscess, empyema Acute ischemic stroke Hypoxic ischemic encephalopathy Brain masses Hydrocephalus ◦ Result of increased production or decreased absorption of cerebrospinal fluid (CSF). ◦ Hydrocephalus can result in massive enlargement of the ventricles. ◦ Acute hydrocephalus may cause damage to the ependyma (the lining of the ventricles) which results in oedema of the periventricular white matter. This is known as transependymal seepage/edema Infection-Meningitis, encephalitis, abscess, empyema ◦ Inflammation of the meninges, brain by bacterial, viral or fungal ◦ This later may result intracranial abscess collection or subdural empyema. ◦ Need contrast administration ◦ Early CT findings may be normal ◦ subtle hydrocephalus ◦ hyperdensity around basal cisterns (especially in tuberculosis) ◦ Leptomeningeal enhancement ◦ Complication: encephalitis, brain abscess, subdural empyema Acute ischemic stroke ◦ Initial CT is often normal ◦ The main purpose of performing a CT is to exclude intracranial haemorrhage. ◦ Subtle low density in the affected territories. ◦ Important signs include the 'hyperdense artery' sign and the 'insular ribbon' sign.  CEREBRAL VASCULAR TERRITORIES ABOVE LATERAL VENTRICLE LEVEL OF INSULA LEVEL OF CEREBELLUM Hypoxic ischemic encephalopathy ◦ older children: drowning and asphyxiation remain common causes ◦ adults: more often a result of cardiac arrest or cerebrovascular disease, with secondary hypoxemia/hypoperfusion ◦ diffuse edema with effacement of the CSF- containing spaces ◦ decreased cortical grey matter attenuation with a loss of normal grey-white differentiation ◦ decreased bilateral basal ganglia attenuation Intracranial masses ◦ Intracranial masses are classified either as intra- axial lesions (in the brain) or extra-axial lesions (outside the brain). The distinction is not always easy to determine. ◦ Intracranial masses can be intra or extra-axial ◦ Single intra-axial lesions are usually primary malignant lesions ◦ Multiple intra-axial lesions are usually metastatic ◦ Meningiomas - the commonest extra-axial masses - are located in close proximity to a meningeal surface ◦ Cerebral abscess is an important differential diagnosis of a ring enhancing mass QUIZ TIME !!!! LEFT MCA INFARCT RIGHT SUBDURAL HAEMORRHAGE SUBARACHNOID HAEMORRHAGE LEFT TEMPORAL BONE FRACTURE LEFT MCA INFARCT RIGHT BASAL GANGLIA HAEMORRHAGE WITH MASS EFFECT AND HERNIATION BILATERAL SUBDURAL HAEMORRHAGE LEFT FRONTAL SUBARACHNOID HAEMORRHAGE LEFT SKULL FRACTURE SUBARACHNOID AND SUBDURAL HAEMORRHAGE