 Hello everyone, I am Dr. Raina Tembe and today we shall be discussing about the normal MRI brain anatomy. Let us start by having a look at the cerebral hemispheres. The cerebral hemispheres lie above the tentorium cerebelli and are conventionally divided into the frontal, parietal, occipital and temporal lobes by the various salsae and fissures. The central sulcus, also known as the rolandic fissure, forms the boundary between the frontal and the parietal lobes, separating the motor cortex in the pre-central gyrus from the sensory strip in the post-central gyrus. Its identification is important when surgery is planned in the vicinity of the motor cortex. So how do we identify the central sulcus? On axial imaging, we first identify the superior frontal sulcus, separating the superior and middle frontal gyrus. At its posterior limit, it forms a right angle with the pre-central sulcus. The next sulcus posterior to it is the central sulcus. On midline sagittal images, we first identify the cingulate sulcus which runs superior to the cingulate gyrus. At its posterior limit, almost vertically above this plenium of the corpus callus, it divides. The marginal sulcus ascends to the vertex. The surface notch immediately anterior to it in the cortex is the central sulcus. On the lateral sagittal images, a y-shaped sulcus is formed by the anterior horizontal ramus of the inferior frontal gyrus and the ascending ramus of the sylvian fissure. The next major fissure posteriorly is the pre-central sulcus with the central sulcus being the next major fissure posteriorly. The parito-oxipital fissure separates the parietal and the occipital lobes. The sylvian fissure separates the frontal and parietal lobes from the temporal lobe inferiorly. The cerebral hemispheres are linked by the corpus callus. The corpus callus is a myelinated tract which appears hyperintense on T2 weighted images and hyperintense on T1 weighted images. On sagittal section, it appears as a curved structure. The genu or the rostrum is the anterior most portion which blends into the anterior commissure. The genu curves posteriorly and superiorly towards the body and then to the splenium of the corpus callus. The splenium of the corpus callus is the most posterior portion of the corpus callus. The fibres of the corpus callus sweep anteriorly into the frontal lobe known as the forceps minor and into the occipital lobe where they are known as the forceps major. Let us have a look at the basal ganglia. The basal ganglia consists of the cordate nucleus, the lentiform nucleus, the clostrum and amygdala. The amygdala is associated with the limbic system and we shall be discussing about it in a separate lecture. The cordate nuclei are C-shaped structure lying along the lateral ventricle. The head of the cordate nucleus indents the frontal horn of the lateral ventricle with the body lying adjacent to the body of the lateral ventricle. The tail of the cordate nucleus lies above the temporal horn of the lateral ventricle and is not readily identified on MRI images. The lentiform nucleus is divided into two by a sheet of white matter into a smaller medial component which is called the globus pallidus and a larger lateral component called as the putamen. The cordate and the lentiform nuclei are together known as the corpus triatum. The clostrum is a thin sheet of grey matter interposed between the grey matter of putamen and insula. It is separated from the putamen by the white matter of the external capsule and from the insula by the white matter of the extreme capsule. The upper motor neuron fibres arising from the primary cortex join the corona radiata and converge on the internal capsule which forms the medial boundary of the lentiform nuclei. It is a milliliter track appearing hypo intense on T2 weighted images. On axial section it appears V shaped with the genu pointing medially separating the anterior and the posterior limbs. The corticobulbar fibres are present in the genu and the corticospinal fibres are present in the posterior limb. These corticospinal fibres have relatively low myelin density and may appear as rounded foci of high signal intensity on T2 weighted images. The brain stem comprises of the midbrain of the pons and the medulla. The midbrain is also known as the mesencephalon and the pons, medulla and cerebellum together constitute the rhombencephalon. Let us have a look at the midbrain. The midbrain consists of pale cerebral peduncles and a dorsal tectum. Each cerebral peduncle consists of the crust cerebrine and the tegmentum which are separated by a pigmented grey matter tract known as the substantia nigra. The crust cerebrine contains the corticospinal fibres. The tegmentum lies ventral to the aqueduct of the sylvius and contains many nuclei amongst which the red nucleus can be easily identified at the level of the superior colliculus. The nuclei of the cranial nerves third and fourth are situated within the midbrain. The cavity of the midbrain is the cerebral aqueduct. The tectum lies posterior to the aqueduct and consists of four colliculi or quadrogeninal bodies. The superior colliculi is associated with the visual reflex and the inferior colliculi is associated with the auditory reflex. The pons has a bulbous ventral portion and a dorsal tegmentum. The ventral portion is continuous with the cerebral peduncles of the midbrain and contains the corticospinal fibres. It mainly contains the transverse fibres which pass posterior laterally as the middle cerebellar peduncles. The dorsal tegmentum contains the cranial nerve nuclei of fifth, sixth, seventh and eighth nerves. The medulla is closed inferiorly around the central canal. This closed medulla extends from the level of foramen magnum to obex. The closed medulla appears pure shaped on axial imaging and may be rotated. The anterior eminences are formed by the pyramids and the posterior column form the posterior eminences. At the level of foramen of magendi, the medulla appears square shaped on either side between the ventral median fissure and the anterior lateral sulcus is an elevation called as the pyramid. Lateral to this is another elevation called as the olive. On the lateral surface of the medulla, there is an indentation corresponding to the post-olivary sulcus. On the dorsal surface of the medulla, we can identify the dorsal median sulcus. On either side are the fasciculus cuneatus and gracilis transmitting the posterior column fibres. Further cranially, the anterior eminences are formed by the pyramids and olive. The posterior eminences become more prominent forming the inferior cerebellar peduncles. The dorsal surface of the medulla becomes the floor of the 4th ventricle. Along the lateral aspect, the 4th ventricle communicates through the foramen of Lushka with the cerebellar pontine angle systems. This is an important pathway for the spread of the intraventricular tumors into the subarachnoid space. The medulla contains the cranial nerve nuclei of 9th, 10th, 11th and 12th norms. The cerebellum lies posterior to the brainstem. The cortical mantle of the cerebellum overlies the central white matter core. The various folia and the interbening selchi are almost parallel to one another. The grey matter of the cerebellum has a tree-like configuration in section and is called as the arborvite. The cerebellum consists of medline wormus which is separated by a paramedian sulcus from the cerebellar hemispheres. The deep transverse fissure divides the cerebellar hemispheres and wormus into three loops each of which is made up of multiple lobules. The primary fissure separates the anterior lobe from the posterior lobe and the posterior lateral sulcus separates the floccular nodular lobe from the posterior lobe. The nodule is the only lobule of the floccular nodular lobe and can be identified posterior to the 4th ventricle. The flocculus is largely separate from the rest of the cerebellum and can be seen extending laterally inferior to the vestibular cochlear nerve. The cerebellar tonsils can also be identified line posterior to the medulla. Three cerebellar peduncles arise from the cerebellum. The inferior cerebellar peduncle or the vestiform body is vertically oriented and passes to the medulla. The middle cerebellar peduncle also called as the brachium pontus is horizontally oriented and passes to the pons. The superior cerebellar peduncle of the brachium conjunctivin is vertically oriented and passes to the midbrain. It forms the part of the lateral wall of the 4th ventricle. The diencephalon is situated between the cerebral hemispheres and brainstem and borders the 3rd ventricle. It consists of the thalamus, the pineal gland, habanular commissure and the hypothalamus. The habanular commissure and pineal gland are together known as the epithalamus. The pineal gland is an ovoid gland situated between the two superior colliculi in the posterior wall of the 3rd ventricle. Two laminae can be seen arising anteriorly from the pineal gland. The superior lamina is the habanular commissure and the inferior lamina is the posterior commissure. The anterior commissure forms the anterior limit of diencephalon. It consists of myelinated fibres within the lamina terminalis. The thalamus are olive shaped paired nuclear masses forming the lateral walls of the 3rd ventricle. They are opposed in the midline at masa intermedia or interthalamic adhesion and are separated from the lentiform nuclei by the posterior limb of the internal capsule, the palvinar projects over the midbrain. The hypothalamus forms the part of the floor and lateral walls of the 3rd ventricle. The infantibulum lies posterior to the optic chiasm and passes to the pituitary gland. Its width varies in different individuals but it should not exceed that of the basilar artery. The pituitary gland fills up the pituitary fossa and is situated above the sphenoid sinus with cavernous sinus on each side. The height of the pituitary gland varies with age but it should not exceed more than 9 millimetre. In females of child-bearing age, the pituitary gland has a convex superior margin. The anterior and posterior lobes of the pituitary gland can be identified separately. The posterior lobe of the pituitary appears hyper-intense on T1-betered images due to the presence of the neuro-secretary granules within. In neonates, the pituitary may appear uniformly hyper-intense. The limbic system comprises of the limbic lobe, olfactory apparatus and septal areas. We shall be discussing this separately. Let us have a look at the cerebral ventricles. In young adults, the ventricular system normally contains 20 to 25 ml of cerebrospinal fluid. The lateral ventricles are C-shaped cavities with corpus callus as their roof. Each lateral ventricle has a frontal horn or the anterior horn which projects into the frontal lobes anterior to the interventricular foramen of mondrone and body which is posterior to the interventricular foramen. The each lateral ventricle has a temporal horn and an occipital horn projecting into the temporal and the occipital lobes respectively. The third ventricle is a narrow midline structure with diencephalon as its boundaries. The fourth ventricle appears triangular in sagittal section. It has an anterior floor and a roof with two sides converging to a posteriorly directed apex. The floor of the fourth ventricle or the rhomboid fossa is formed by the posterior surface of the pons and the upper medulla. The upper part of the roof above the apex is formed by the superior cerebellar peduncle and superior medullary vellum. The roof below the apex is formed by the inferior medullary vellum. The inferior medullary vellum has a midline aperture called as the foramina of magenta. The CSF is formed by the coroid plexuses. The coroid plexuses are imaginated into the medial walls of the lateral ventricle and into the roofs and the floors of the third and fourth ventricles. The CSF flows cordially from the lateral ventricles into the third ventricles and fourth ventricle. The CSF then flows into the basal cisterns and into the cortical subarachnoid spaces overlying the cerebral hemispheres and is absorbed by the arachnoid villi into the venous system. A small amount of CSF circulates around the spinal cord. The subarachnoid cisterns are situated at the base of the brain and around brainstem, free edge of temporium and major arteries. These cisterns communicate freely with each other. The cisterna magna lies between the medulla and the posterior inferior surface of cerebellum. It receives CSF from the fourth ventricle via the foramina of magendi and lushka and is continuous below with the spinal subarachnoid space. It contains the vertebral and posterior inferior cerebellar arteries and ninth, tenth and eleventh cranial nerves. When the cistern is very large, it is called as the megacisterna magna. The pontine cistern is anterior to the pons and medulla and contains the basilar artery and fifth to twelfth cranial nerves. It is continuous with the interpericular cistern superiorly and the quadroginal plate cistern posteriorly. The chiasmatic or supracellar cistern extends from the infundibulum to the posterior surface of the frontal lobe and it has anchors on its ebber side. It contains the part of the sylvian fissure and the circle of villus. Superior to the supracellar cistern is the cistern of lamina terminalis containing the anterior communicating artery and superiorly is the callusil cistern containing the peri-callusil artery. The cistern of vealum interpositum is limited anteriorly by the interventricular foramen of mondro. It communicates posteriorly with the quadroginal plate cistern and contains the internal cerebral vein. The quadroginal plate cistern lies along the superior surface of the cerebellum and continues superiorly towards the spleenium of the corpus callusin. It is the location of the venus confluence of the vein of gallin with the inferior sagittal and straight sinus and contains the posterior cerebral, posterior coroidal, superior cerebellar arteries and trochlear nerves. The ambient cistern surrounds the midbrain and contains the posterior cerebral and superior cerebellar arteries the basal veins of versenthal and the trochlear nerves. The cerebellar pontine angle cistern is limited medially by the pons posteriorly by the floculus of the cerebellum and laterally by the petrous bone. It transmits the facial and vestibular cochlear nerve the antero inferior cerebellar artery the petrosil vein of dandy and trigeminal nerve in the anterior portion. Lastly, let us have a look at the meninges. The meninges have three constituent parts the fibrous dura mater avascular arachnoid matter and the vascular paya matter the subdural space is a potential space between the dura and arachnoid into which hemorrhage or pus may occur its existence is controversial in normal individuals the subarachnoid space is between the arachnoid and paya and contains CSF the paya is closely applied to the cerebral surface the dura has two layers the outer layer is the endosteum and the inner layer covers the brain and forms the falx and tentorium the cranial dura has two layers which separates to enclose the dural venous sinuses the dura appears relatively hyper intense on MRI the falx may occasionally calcify or ossify appearing as region of signal void due to calcification or hyper intense due to the fact within the maroon the falx cerebrae is sickle shaped and extends from the crystal ally anteriorly to the internal occipital protuberance posteriorly it forms an incomplete partition between the cerebral hemispheres the tentorium cerebellyle is attached from the posterior plenoid process along the petrus ridges to the internal occipital protuberance its upper free medial border surrounds the midbrain which passes through the tentorial incisura the anchis and the posterior cerebral arteries lie above the free edge there at risk of compression against the tentorial edge when there is raised intracranial pressure in the supratentorial compartment the free border anteriorly encloses the cavernous sinus and attaches anteriorly to the anterior clenoid process the falx cerebelli is attached superiorly to the posterior part of tentorium it terminates just above the foramen magnum the diaphragm cell forms an incomplete roof over the pituitary gland and is pierced by the infundabulum