For educational and institutional use. This test bank is licensed for noncommercial, educational inhouse or online educational course use only in

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1 For educational and institutional use. This test bank is licensed for noncommercial, educational inhouse or online educational course use only in educational and corporate institutions. Any broadcast, duplication, circulation, public viewing, conference viewing or Internet posting of this product is strictly prohibited. Purchase of the product constitutes an agreement to these terms. In return for the licensed use, the Licensee hereby releases, and waives any and all claims and/or liabilities that may arise against ASRT as a result of the product and its licensing.

2 Sectional Anatomy Essentials Module 3: The Brain 1. The Brain Welcome to Module 3 of Sectional Anatomy Essentials The Brain. This module was written by Michael A. Manders, BS, R.R.A., R.T. (R), and Jeffrey D. Houston, MD. 2. License Agreement and Disclaimer 3. Objectives After completing this module, you will be able to: Explain the surface anatomy of the brain, including the structure of the meninges. Locate the structures of the brain s ventricular system. Describe the arterial blood supply to the brain. Identify the major venous sinuses that carry blood from the brain to the internal jugular veins. Name the lobes of the cerebrum. Describe the location and structure of the cerebellum. Identify the components and explain the function of the limbic system. Describe the relationships of the basal ganglia. Locate and identify the anatomical structures of the brainstem. Name the 12 cranial nerves, state the foramina that serve as passageways for each pair of nerves and describe the function of each nerve. 4. Introduction In this module, we display most of the three-dimensional anatomy of the brain using a single patient scanned in the axial, sagittal and coronal planes. Because you can easily lose your frame of reference when viewing cross-sectional images, the location of the featured slice on many slides will be displayed on adjacent localizer images of the other 2 planes, like the image shown here. 5. Introduction The magnetic resonance (MR) imaging scan used for this module consisted of 26 slices and was conducted on a 31-year-old man with no known pathology. To emulate the actual scan, we compiled the images into an animation you can control. Use the slider bar in this animation to scroll through the images. Click on the next button when you are ready to proceed. We ll use this type of animation throughout the module to help you learn the appearance and location of the brain anatomy. For consistency and similarity to the appearance of computed tomography (CT) images, most MR images for this module were obtained using a T2 FLAIR pulse sequence. FLAIR stands for fluid-attenuated inversion recovery, which means that the fluid signal is suppressed, or appears dark on the image. Therefore, the image maintains the detail of T2 weighting, but cerebrospinal fluid appears black, just as it does on CT images. If a particular structure is better visualized using another pulse sequence or with CT, we first show the structure s location on the T2 FLAIR images and then show additional images in which the structure is best demonstrated.

3 6. The Brain The surface of the brain has a very intricate appearance, full of valleys and mountains. These valleys are called sulci, or fissures, and the mountains are called gyri. Next, we ll discuss the major sulci and gyri of the brain. 7. Sulci The first major sulcus we ll talk about is the longitudinal fissure. It s the midline sulcus that divides the right and left hemispheres of the brain. The lateral sulcus, also referred to as the Sylvian fissure, divides the temporal lobe of the brain from the overlying frontal and parietal lobes. An interesting fact about the Sylvian fissure is that although it s found in both cerebral hemispheres, it typically is longer in the left hemisphere. The last major fissure we ll cover is the central sulcus, also known as the fissure of Rolando. This sulcus extends transversely across the brain and divides the frontal lobe from the parietal lobe. 8. Gyri Two major gyri are important to recognize: the precentral gyrus and the postcentral gyrus. The precentral gyrus is located anterior to the central sulcus and contains the primary motor cortex, meaning it s responsible for controlling movements of various body parts. The postcentral gyrus is located posterior to the central sulcus and contains the primary somatosensory cortex of the brain, meaning it s responsible for sensations we feel on our skin while touching or being touched. Now let s talk about the internal coverings of the brain, the meninges. 9. Meninges Meninges are the layers of membranes that cover the brain. There are 3 meninges: the dura mater, the arachnoid mater and the pia mater, all of which have different features that help them protect the brain. 10. Dura Mater As we advance medially from the skull, the first layer we encounter is the dura mater, which is Latin for tough mother. The dura mater is made up of dense fibrous tissue and has 2 layers: an outer, periosteal layer, which serves as the inner periosteum of the skull, and an inner meningeal layer. In some areas, the layers separate and the inner layer protrudes centrally to form sheet-like folds, or reflections, that divide portions of the brain. The 4 primary areas where the divisions occur are the falx cerebri, tentorium cerebelli, falx cerebelli and the diaphragma sellae. Let s talk about these structures in more detail. 11. Brain Reflections The falx cerebri extends into the longitudinal cerebral sulcus to divide the right and left cerebral hemispheres. The tentorium cerebelli extends horizontally to divide the cerebellum from the cerebrum. The falx cerebelli extends vertically to divide the right and left cerebellar hemispheres. The final and smallest dural reflection we ll discuss is the diaphragma sellae. The diaphragma sellae forms a roof over a depression in the sphenoid bone, which houses the pituitary gland.

4 12. Head Trauma The dura is of particular importance in the radiology of head trauma. A progressively accumulating collection of blood, termed an epidural hemorrhage, can become trapped between the skull and dura and produce considerable extrinsic mass effect on the brain. Extrinsic implies that the mass effect arises outside the brain, such as an extra-axial hemorrhage, as opposed to intrinsic mass effect such as a tumor, which is inside the brain. 13. Arachnoid Mater The arachnoid mater is the next layer as we travel medially and is named for its spider-web appearance. It also is made up of fibrous tissue, although the cells are not as densely packed as in the dura mater. A thin lining of flat epithelial cells that is impermeable to fluid covers the inner arachnoid mater. The arachnoid mater cushions the brain, and unlike the next deeper layer, it does not follow the minor fissures and convolutions of the brain. Traumatic bleeding also can accumulate between the dura and the arachnoid and is called a subdural hemorrhage. Like an epidural hematoma, a subdural hematoma can produce significant extrinsic mass effect on the brain. On this axial CT image, bilateral frontal subdural hematomas efface the underlying cerebral sulci. Note the bright, or high attenuation, fluid on the patient s right side, which indicates recent hemorrhage. Compare this area to the dark, or low attenuation, fluid on the patient s left side, which indicates an older hemorrhage. 14. Pia Mater The deepest meningeal layer of the brain is the pia mater, which in Latin means soft mother. This layer is very thin and delicate, and closely follows all the gyri and sulci of the brain. Like the other layers, the pia mater is composed of fibrous tissue, and similar to the inner arachnoid mater, the outer pia mater has a lining of flat epithelial cells that is impermeable to fluid. The space between the arachnoid mater and pia mater is called the subarachnoid space. It is filled with cerebrospinal fluid and provides additional cushioning for the brain. 15. Knowledge Check 16. Knowledge Check 17. Knowledge Check 18. The Flow of Cerebrospinal Fluid Before we can discuss the ventricular system, it s important to understand cerebrospinal fluid, or CSF. CSF allows the brain to float within the cranium and provides critical cushioning against the bouncing and jolting the head is subjected to in a normal day. This animation shows how CSF circulates within the cranium. CSF flows from the lateral ventricles into the third ventricle via the interventricular foramina. From the third ventricle, it travels through the cerebral aqueduct into the fourth ventricle. The CSF continues from the fourth ventricle into the subarachnoid space of the brain and spinal cord.

5 The arachnoid villi, or arachnoid granulations, are small protrusions of the subarachnoid space into the dura mater. The CSF is reabsorbed into the venous sinuses through these protrusions. We ll describe the ventricles in more detail later in this module. 19. Choroid Plexus Look at this illustration. It shows the location of the structures that are involved in the manufacture of CSF. CSF is produced by modified ependymal cells that are found primarily in clusters called choroid plexuses, and also in the lining of the walls of the majority of the ventricular system. On cross-sectional imaging, choroid plexuses are most visible in the lateral ventricles, but also can be seen in the third and the fourth ventricles. This midline sagittal illustration makes it look like the lateral ventricle is superior to the corpus callosum when in fact the corpus callosum actually overlies the roof of the lateral ventricles. In a midline image, you can t see the lateral ventricles because the thin septum pellucidum, which divides them, is in the way. As you extend laterally to either side the roofs of lateral ventricles slightly bulge superiorly above the level of the corpus callosum. What we see in this illustration is the lateral ventricle superimposed from a paramedian slice. 20. Choroid Plexus This is slice 13 of the MR brain scan used in this module. Note the location of the choroid plexus, as indicated on this slice. 21. Choroid Plexus Scroll through this animation. Locate the choroid plexus on slices 13 and 14 of the series. 22. Lateral Ventricles The lateral ventricles are located in each cerebral hemisphere. They look like ram horns when viewed in the coronal plane. Each lateral ventricle is divided into 3 horns: the frontal, or anterior, horn; the occipital, or posterior, horn; and the temporal, or inferior, horn. The triangular area where the 3 horns converge is called the trigone, or atrium, and the central portion of each lateral ventricle is referred to as the body. 23. Lateral Ventricles Look at these images. They are the localizer images from slice 19 of the MR scan. The image on the left is a coronal view of the lateral ventricles, as indicated by the arrows. The image on the right is a parasagittal view of the brain showing a lateral ventricle. It is interesting to note that the temporal horns of the lateral ventricles are mostly compressed in young individuals. In older patients, the temporal horns are usually more capacious as a result of cerebral volume loss and become visible farther anteriorly. 24. Lateral Ventricles Look at these axial images of the brain. The image on the left, slice 16, provides a good view of the lateral ventricles. The image on the right, slice 12, shows the posterior horns of the lateral ventricles.

6 25. Lateral Ventricles Recall the location of the lateral ventricles as shown in the previous 2 slides. Scroll through this animation and note the curvature of the ventricles and how their location relates to other areas of the brain. 26. Septum Pellucidum The lateral ventricles are divided by a thin membrane called the septum pellucidum, a landmark often used to determine if there is midline shift. The 2 leaves that make up the septum pellucidum are separate in utero and typically fuse posteriorly to anteriorly around the time of birth. Failure of the anterior portion of the leaves to fuse produces a duplicated, or split, septum pellucidum with intervening fluid. This common developmental variant is referred to as a cavum septum pellucidum. A cavum septum pellucidum et vergae, or cavum vergae, is also a developmental variant in which the leaves of the septum pellucidum fail to separate and extend to the posterior wall of the lateral ventricles. The image on the right shows a cavum vergae. 27. Third Ventricle The illustration on this slide shows the location of the third ventricle from a sagittal view. The third ventricle is located midline, inferior to the level of the bodies of the lateral ventricles. It is bordered by the hypothalamus and thalamus bilaterally, and anteriorly by a thin membrane called the lamina terminalis. In the majority of people, a band of tissue called the interthalamic adhesion, or massa intermedia, extends transversely through the third ventricle to bridge the thalami. On this axial MR image, note the location of the third ventricle. 28. Third Ventricle The CSF travels from the lateral ventricles to the third ventricle via the paired interventricular foramina, commonly referred to as the foramina of Monro. The small foramina of Monro are difficult to see on cross-sectional imaging except in cases like the one shown here. In these MR images, you can see choroid plexus tumors extending through both foramina of Monro between the third and both lateral ventricles. Note the dark tumors surrounded by bright CSF on the T2- weighted axial image on the left and the bright rims of the tumors delineating them from dark CSF on the T1-weighted coronal image on the right. Also note that the septum pellucidum is bowed toward the patient s left on the coronal image. 29. Third Ventricle Let s return to our patient without any known pathology. Scroll through these images to see the third ventricle. 30. Fourth Ventricle From the third ventricle, CSF travels through the cerebral aqueduct, also called the aqueduct of Sylvius, to the fourth ventricle. The fourth ventricle is located within the posterior pons and upper medulla, anterior to the cerebellum. Thin membranes called the superior and inferior medullary vela form what is termed the roof of the ventricle, although this anatomic roof is actually located posteriorly and the floor is located anteriorly. The lateral walls of the fourth ventricle are formed by the cerebellar peduncles. The paired lateral apertures, or foramina of Luschka, supply the subarachnoid space, specifically the cerebellopontine angle cistern, with CSF and arise from the lateral angles of the fourth ventricle. Extending posteroinferiorly from the

7 fourth ventricle is the median aperture, also called the foramen of Magendie, which also supplies CSF to the subarachnoid space, specifically the cisterna magna. We ll discuss the subarachnoid cisterns in more detail later in this module. 31. The Fourth Ventricle The fourth ventricle is classically described as having a diamond-shape on cross-section specimens of the brain and as seen on axial images. The fourth ventricle has a tent-shape when viewed in the sagittal plane. 32. The Fourth Ventricle This MR scan was performed on a different patient using T2 weighting. Note how the fourth ventricle is better visualized than in the T2 FLAIR images we ve been viewing. Recall that in a T2- weighted image fluid appears white and bone appears black. 33. The Fourth Ventricle The fourth ventricle is visualized in this set of MR images. Scroll through the animation to examine the fourth ventricle more closely. 34. Knowledge Check 35. Knowledge Check 36. Knowledge Check 37. Subarachnoid Cisterns Although the subarachnoid space is mostly narrow, there are places where it widens. These spaces are collectively called the subarachnoid cisterns. The term basal cisterns is frequently used interchangeably with subarachnoid cisterns by radiologists although basal cistern properly refers to one specific cistern known as the interpeduncular cistern. The largest of these cisterns are typically named for bordering structures. Let s talk about the cisterns in more detail. 38. Cisterna Magna One of the largest of the subarachnoid cisterns is the cerebellomedullary cistern, or what is commonly known as the cisterna magna, located posterior to the medulla oblongata, anterior to the inferior occipital bone and inferior to the cerebellar hemispheres. 39. Cisterna Magna Scroll through these images to locate the cisterna magna. 40. Mega-Cisterna Magna A common developmental variant is a mega-cisterna magna, which refers to a large cisterna magna without associated abnormalities of the cerebellum or fourth ventricle. You can see a mega-cisterna magna in these images.

8 41. Interpeduncular Cistern Another key subarachnoid cistern is the interpeduncular cistern, which is located between the cerebral peduncles. The interpeduncular cistern is particularly important because it often is the first place that subarachnoid hemorrhage accumulates; high attenuation, or bright, hemorrhage within the cistern can lead to inadequate visualization of this cleft, which normally is filled with low attenuation, or dark, CSF on CT scans. Now look at the axial CT image on the right. Note the blood-filled interpeduncular cistern of this patient with extensive subarachnoid hemorrhage. 42. Pontine Cisterns The interpeduncular cistern connects to the pontine cistern, also known as the pre-pontine cistern, which is located anteroinferior to the pons. 43. Cerebellopontine Cisterns The pontine cistern communicates with the cerebellopontine cisterns, or cerebellopontine angle cisterns, which are commonly abbreviated as the CPA cisterns. The cerebellopontine cisterns are located medial to the petrous portions of the temporal bones. The structures within the cerebellopontine cisterns include the anterior inferior cerebellar arteries and the fifth, seventh and eighth cranial nerves. We ll discuss each of these structures later in the module. 44. Cerebellopontine Cisterns The image on the left was acquired using a FLAIR sequence. Recall that subarachnoid cisterns contain CSF. It s difficult to see the CSF in the FLAIR sequence because fluid appears black, as does the adjacent bone. However, if we look at the T2-weighted image on the right, you can differentiate between fluid and bone because in a T2-weighted image, fluid appears white and bone appears black. 45. Ambient Cisterns Next, we find the ambient cisterns, which are located bilaterally along the midbrain. The ambient cisterns connect to the quadrigeminal, or superior, cistern, which is located posterior to the quadrigeminal plate. 46. Suprasellar Cistern The last cistern we ll discuss is the suprasellar, or chiasmatic, cistern. This cistern also contains important structures, including the optic nerves and chiasm, as well as the circle of Willis. 47. Subarachnoid Cisterns Scroll through this animation to review the location of all of the subarachnoid cisterns. 48. Knowledge Check 49. Knowledge Check 50. Knowledge Check

9 51. Dural Sinuses The dural sinuses are large channels that receive blood from all the internal and external veins of the brain and carry it to the internal jugular veins. These channels are located between the 2 layers of the dura mater. Although the dural sinuses may look like veins, they consist of dura mater lined with endothelial cells and lack the layers that make up a typical vein. 52. Dural Sinuses Let s talk about the dural sinuses. Look at this illustration. We re going to cover the following structures: the superior sagittal sinus, inferior sagittal sinus, the great cerebral vein of Galen, the confluence of sinuses, the transverse sinuses, the sigmoid sinuses and the cavernous sinuses. 53. Superior and Inferior Sagittal Sinus One of the major dural sinuses, the superior sagittal sinus, runs midline, following the superior anteroposterior curvature of the skull from the crista galli to the internal occipital protuberance. The inferior sagittal sinus runs parallel to the superior sagittal sinus along the inferior border of the falx cerebri until it joins the great cerebral vein of Galen to become the straight sinus. 54. Confluence of Sinuses Typically the superior sagittal sinus terminates into one of the transverse sinuses and the straight sinus into the other transverse sinus. Venous blood from the straight sinus, the superior sagittal sinus and the occipital sinus converges at a point called the confluence of sinuses. The term torcular herophili is often used interchangeably with confluence of sinuses although is more properly reserved for the concavity in the inner table of the occipital bone that houses the confluence of sinuses. Considerable variation in the venous anatomy can result in blood from up to five sinuses communicating at the confluence: the superior sagittal sinus, the straight sinus, the occipital sinus, and both transverse sinuses. The venous blood travels through the transverse sinuses, which follow the lateral curves of the skull at the level of the internal occipital protuberance, until the blood passes through the tentorium cerebelli. At this point, the channels become the sigmoid sinuses and empty into the internal jugular veins. 55. Cavernous Sinuses The last sinuses we ll discuss are the cavernous sinuses, located bilaterally along the sella turcica. The cavernous sinuses are unique dural sinuses because the internal carotid arteries and multiple cranial nerves traverse these structures. The cavernous sinuses drain into the superior and inferior petrosal sinuses. 56. Dural Sinuses Look at this illustration. Let s review the location of each of the structures that we discussed. Find the inferior sagittal sinus. Next, identify the superior sagittal sinus. Identify the transverse sinus. Locate the sigmoid sinus. Find the cavernous sinus. 57. Knowledge Check 58. The Cerebral Arteries Cross-sectional imaging modalities permit visualization of vascular structures that once were only visible by using intra-arterial injections of contrast media during catheter-based

10 angiography. CT angiography typically is performed with intravenous iodinated contrast media. MR angiography, as seen on this slide, uses various techniques, such as gadolinium-based contrast enhancement and noncontrast time-of-flight imaging, in which flowing blood appears brighter than the adjacent tissues. 59. Blood-Brain Barrier When discussing cerebral vascular anatomy, it s important to first mention the blood-brain barrier. Look at this illustration. On the left side is a brain capillary and the vertical black arrows represent blood flow. The blood-brain barrier is a thin membrane composed of endothelial cells that have tight junctions and surround the capillaries anywhere the vessels come in contact with the brain. This membrane blocks the diffusion of particles like bacteria, while allowing small molecules like oxygen and carbon dioxide to disperse readily. Now let s examine the individual vessels that transport blood to the brain. 60. Cerebellar Arteries The right and left posterior inferior cerebellar arteries, known by the acronym PICA, arise from the distal right and left vertebral arteries. Each PICA has medial and lateral branches and supplies blood to the posteroinferior aspect of the cerebellum and the choroid plexus of the fourth ventricle. The vertebral arteries then converge to form the basilar artery at the level between the medulla oblongata and the pons. As the basilar artery travels anteriorly, the right and left anterior inferior cerebellar arteries, known by the acronym AICA, branch off and supply blood to the anteroinferior portion of the cerebellum. Next, the pontine arteries branch off the basilar artery at 90-degree angles to the right and left, approximately 3 to 5 vessels on each side. These arteries supply blood to the pons and adjacent structures. The right and left superior cerebellar arteries, known by the abbreviation SCA, are the next vessels to arise from the basilar artery. The SCAs supply blood to the superior portion of the cerebellum, along with parts of the midbrain. Branches of the SCA also travel through the pia mater. Immediately superior to the origins of the SCAs, the basilar artery bifurcates into the right and left posterior cerebral arteries, bringing us to the circle of Willis. 61. Circle of Willis Look at this illustration of the circle of Willis. The circle of Willis comprises 5 arteries: paired anterior cerebral arteries, a single anterior communicating artery, paired internal carotid arteries, paired posterior cerebral arteries and paired posterior communicating arteries. The internal carotid arteries make an S-shaped, tortuous run through the cavernous sinus. Just after exiting the cavernous sinus, the ophthalmic arteries branch off to bring blood to the eyes. The internal carotid artery then converges with the rest of the arteries in the circle of Willis to form a circular shape, sort of like a traffic roundabout. Cars enter the roundabout from connecting streets or, in this case, blood enters the circle from the basilar and internal carotid arteries. 62. Circle of Willis The actual shape of the circle is formed by the anterior and posterior communicating arteries, which we ll discuss in a moment. From there, blood flows through the anterior, middle or posterior cerebral arteries. Because the middle cerebral arteries are not considered part of the circle of Willis, we ll cover them later in this module. The anterior and posterior cerebral arteries are responsible for supplying blood to specific parts of the brain, so what happens when there is an occlusion of the basilar or internal carotid arteries?

11 63. Circle of Willis The circle of Willis is unique in that it has its own backup system. Throughout the body, many organs are supplied by only 1 or 2 arteries. If one of these vessels becomes obstructed for a period of time, a phenomenon called collateralization occurs. Collateralization is when the body develops new vessels that can bypass an obstruction. Although the new vessels are not as efficient as the original unobstructed vessel, collateralization can restore some of the lost blood supply to the organ. The brain already has collateralization in place. Look again at this illustration. As you may have noticed, many of the arteries of the brain connect to other arteries, as in the case of the circle of Willis. Let s go back to the roundabout analogy. Without the anterior and posterior communicating arteries, blood would flow from the basilar artery to the posterior cerebral arteries and from the internal carotid arteries to their respective middle and anterior cerebral arteries. Therefore, if one of the internal carotid arteries becomes blocked, the anterior cerebral artery and corresponding part of the brain would not receive the needed blood supply. However, given an intact circle of Willis, if that same internal carotid artery is blocked, blood from the basilar and other internal carotid artery could flow through the posterior and anterior communicating arteries to restore some blood supply and buy time to save the affected part of the brain. 64. Cerebral Arteries Now, back to the cerebral arteries. First, we ll discuss the anterior cerebral arteries, known by the abbreviation ACA. Radiology professionals typically focus on the 2 main parts of the ACAs the A1 and A2 segments. The A1 segment extends from its origin at the internal carotid artery to the anterior communicating artery. After passing this point, the A1 segment becomes the A2 segment until it bifurcates into the pericallosal artery and the callosomarginal artery. The middle cerebral arteries, or MCAs, are each divided into 2 main parts, the M1 or horizontal segment and the M2 segment, which represents the insular, or Sylvian, segments. The posterior cerebral arteries, or PCAs, also each have 2 main parts, the P1 segment from the basilar bifurcation to the origin of the posterior communicating segment, and the P2 segment beyond the posterior communicating branch. 65. Cross-sectional Angiography The image on the left is a maximum intensity projection or MIP image from an MR angiography (MRA) scan. The source images from an MRA are processed into MIPs so that the vessels can be rotated both vertically and horizontally, allowing the user to follow their courses in all three dimensions. You can clearly see the major arterial structures of the brain from this single coronal image. The image on the right is a CT angiography (CTA) scan of a different patient. CTAs can be processed to provide images that appear similar to MRAs. 66. Deep Cerebral Veins Multiple veins drain the various deep structures of the brain, the primary ones being the thalamostriate, septal, internal cerebral and basal veins. The thalamostriate vein drains blood from the thalamus and the corpus striatum, which consists of the caudate nucleus, putamen and globus pallidus. The thalamostriate vein converges with the septal vein, which receives blood from the anterior frontal lobe. Eventually, the blood flows into the internal cerebral vein. The internal cerebral vein converges with the basal vein of Rosenthal, which arises in the medial

12 temporal lobe, and the blood then flows into the great cerebral vein of Galen before finally draining into the straight sinus. 67. Cerebellum The cerebellum, which is Latin for little brain, is located posterior to the pons and inferior to the occipital lobe. It looks like a piece of cauliflower, and its function includes assisting, but not initiating, movement. This image is slice 7 of our MR scan. Let s talk about the structures that make up the cerebellum. 68. Cerebellum Components The cerebellum is made up of 2 hemispheres that are connected by a narrow protruding band of tissue called the vermis. The vermis is a worm-like structure, and in fact, vermis is Latin for worm. Paired, rounded protuberances along the inferior border are called the cerebellar tonsils. 69. Knowledge Check 70. Cerebrum Most people think of the cerebrum when they think of the brain. The largest part of the brain, the cerebrum is made up of gray and white matter and is divided into right and left hemispheres. The gray matter is mostly found superficially, consists of neuron cell bodies and makes up the cerebral cortex. The cortex controls body movement and receives sensory signals. White matter is composed of myelinated axons and is located internal to the cerebral cortex. The myelinated axons within the white matter transmit nerve impulses to and from the cerebral cortex. 71. Pineal Gland The pineal gland is an endocrine structure located just posterior to the third ventricle. It regulates reproductive cycles and the circadian rhythm, which is the day-and-night cycle our bodies go through in a 24-hour period. It also regulates the sleep-wake cycle by secreting the hormone melatonin. This gland tends to calcify, which is a completely normal finding on CT scans. This axial CT scan shows a calcified pineal gland. 72. Corpus Callosum There are 3 primary bundles of white matter found between the right and left cerebral hemispheres, the largest of which is the corpus callosum. The corpus callosum connects the right and left cerebral hemispheres and makes up the roofs of the lateral ventricles in the middle of the brain. It typically is divided into 4 parts, which are better visualized on this T1- weighted image: the rostrum, the genu, the body and the splenium. The rostrum is the most anterior and inferior portion. Slightly superior and anterior to the rostrum is the genu. As the corpus callosum extends posteriorly, it is called the body. The most posterior portion, located superior to the pineal gland, is the splenium. 73. Anterior and Posterior Commissures The other 2 bundles of white matter between the right and left cerebral hemispheres are the anterior and posterior commissures. Look at this axial MR scan to see where these structures are located.

13 Now look at the axial view of the brain with localizers from our sample patient. This image is slice 14. The anterior commissure runs between the anterior portions of the temporal lobes, through the lamina terminalis, which you might recall makes up the anterior wall of the third ventricle. To better visualize the posterior commissure, we ll use a sagittal view of slice 13 and localizers from our sample patient. The posterior commissure is located inferior to the pineal gland and controls pupillary light reflexes. 74. Cerebral Lobes Remember that the cerebrum is divided into right and left hemispheres, but each hemisphere is further divided into 4 or 5 lobes, depending on which source you consult. The 4 primary lobes are the frontal lobe, parietal lobe, occipital lobe and temporal lobe. 75. Insula The question of whether there are 4 or 5 lobes brings us to a structure known as the insula. The insula, also known as the island of Reil, mediates both sensory and motor functions. Although it is commonly called the fifth lobe, some still refer to the insula as part of the temporal lobe. The insula is formed when the gray matter along the lateral border of the temporal lobe folds inward. On axial imaging, it can be seen surrounding the Sylvian fissure. 76. Cerebral Lobes As you might have guessed, the frontal lobe of each cerebral hemisphere is located anteriorly. The frontal lobe is the largest of the cerebral lobes and is separated from the temporal lobe by the Sylvian fissure and from the parietal lobe by the central sulcus. In short, it is responsible for personality and voluntary motor control. The parietal lobe is located posterior to the frontal lobe and superior to the occipital lobe. It is responsible for sensory information and peripheral sensations. The parietal lobe is separated from the temporal lobe by the Sylvian fissure. The temporal lobe is located inferior to the frontal and parietal lobes and anterior to the occipital lobe. It is primarily responsible for auditory sensations, but also is involved with smell and taste. It s important to note that the temporal lobe contains the hippocampus, which we ll discuss in more depth shortly. The occipital lobe is the most posterior lobe of the brain. It is located superior to the cerebellum and is separated from that structure by the tentorium cerebelli. Its primary function is vision. 77. Frontal Lobe These images are slice 19 of our sample patient. In these images, you can see the frontal lobe from both the axial and the sagittal views. 78. Occipital Lobe Slice 12 provides a view of both the occipital lobe and the cerebellum. 79. Parietal Lobe The parietal lobe can be seen from both the axial and sagittal views as demonstrated here on slice 19.

14 80. Temporal Lobe The temporal lobe is best viewed from the sagittal view as seen here on slice 13 of our sample patient. 81. Cerebral Lobes Take a moment to scroll through all 26 slices of the MR scan of our sample patient to see all of the cerebral lobes. 82. Knowledge Check 83. Knowledge Check 84. Knowledge Check 85. Limbic System The limbic system is responsible for the emotional responses of behavior and is located along and within the medial aspects of the temporal lobes, inferior to the corpus callosum. The limbic system consists of different fibrous tracts and has multiple components, including the hippocampi, amygdalae, fornices, and mammillary bodies. Now let s talk about each limbic system structure in more detail as we look at its location on the MR scan of our sample patient. 86. Hippocampus The hippocampus is ultimately responsible for converting short-term memories into long-term memories. It is made up of gray matter and is located in the medial border of the temporal lobe, at approximately the level of the interpeduncular cistern. 87. Hippocampi The hippocampus is an important structure in neuroanatomy because of the association between temporal lobe seizures and a condition called mesial temporal sclerosis. Highresolution MR images of the hippocampus often are obtained in patients with temporal lobe seizures to assess for this condition. The image on the left is slice 13 from our sample patient. Although you can see the hippocampus on this image, it is better visualized in the T1-weighted image on the right from a different patient as T1 weighting is more useful than T2 FLAIR for visualizing pathology in this particular structure. 88. Amygdalae Each amygdala is a mass of gray matter along the medial border of the temporal lobe, but the amygdalae are located more anterior to the hippocampus. The structures are responsible for smell, aggression and sexual behavior. 89. Fornices Of the many tracts that relay signals from the limbic system to the rest of the brain, the most easily identifiable are the fornices. This image is slice 14 of our sample patient. Note the location of the columns of the fornices. Each fornix extends in a C-shape from its respective hippocampus and then joins to form a single tract that makes up the inferior margin of the

15 septum pellucidum. The tracts remain joined as they continue anteriorly until they reach the anterior commissure, where the fornices separate and arch inferiorly to the mammillary bodies. 90. Mammillary Bodies The image on the left is slice 12 from our sample patient. Look at the localizer images to orient yourself to the location of the mammillary bodies. The image on the right is a T2-weighted axial MR scan of a different patient. The mammillary bodies are more readily visible on this image. The mammillary bodies act as a relay structure, receiving signals from the hippocampi and amygdalae, and then routing those signals to the functional areas of the brain. The olfactory bulbs are situated inferior to the frontal lobes of the brain. When the olfactory bulbs receive the sensory inputs of smell, they transmit the signals to the amygdalae. 91. Basal Ganglia and Neighboring Structures The basal ganglia, also referred to as basal nuclei, are a group of subcortical pockets of gray matter that are located at the base of the forebrain. These structures help plan and program movement. The primary parts of each basal ganglion are the caudate nucleus, putamen and globus pallidus. We will also discuss neighboring structures including the thalamus, claustrum and internal and external capsules. 92. Thalami The paired thalami are located along the lateral borders of the third ventricle and are connected to each other via the interthalamic adhesion, also known as the massa intermedia, that extends through the third ventricle. They are joined to the cerebral cortex by many fibrous tracts. Like the mammillary body, the thalamus is a transmission structure. It can be thought of as a shipping warehouse that serves the cerebral cortex. The thalamus both sends and receives packages, or signals, from the cerebral cortex. In some places, the signals travel over long distances, and like any good shipping system, there must be relay stations along the way to keep the packages, or in this case signals, moving in a timely, organized manner. 93. Head of the Caudate Nucleus The first relay station is the caudate nucleus. A C-shaped caudate nucleus parallels each of the lateral ventricles along their lateral borders. Each caudate nucleus contains 3 parts. Anteriorly is the head, which normally can be seen indenting the frontal horn of each lateral ventricle. The body of the caudate nucleus extends posteriorly, following the arch of the lateral ventricle, until it angles first inferiorly, then anteriorly and becomes the tail of the caudate nucleus. The tail eventually ends where it joins the amygdala, which we discussed previously. 94. Lentiform Nucleus The second relay station is the lentiform nucleus. The lentiform nucleus is located within the space central to the C-shaped margin of the caudate nucleus and anterolateral to the thalamus. The lentiform nucleus is divided into 2 parts: the medially located globus pallidus and the laterally positioned putamen. 95. Claustrum The claustrum is a thin layer of gray matter that can be found lateral to the putamen, but medial to the insula. The last portions of the basal ganglia are the different structures that spread out

16 like a highway system, transmitting signals to and from the thalami, caudate nuclei and lentiform nuclei. These tracts of white matter, called the internal and external capsules, help to convey electrical impulses. 96. Internal and External Capsules The corona radiata represents the collection of white matter tracts of the internal capsule and the centrum semiovale. The internal capsule is crescent-shaped with its anterior limb separating the caudate head from the lentiform nucleus, which you recall represents the globus pallidus and putamen. Its posterior limb separates the thalamus from the lentiform nucleus. As it extends superiorly, the internal capsule spreads out like a fan and carries signals all the way to the cerebral cortex. This fan-shaped area is called the centrum semiovale. The external capsule is a thinner tract of white matter than the internal capsule and separates the putamen from the claustrum. The extreme capsule represents a thin tract of white matter extending between the claustrum and the insular cortex. 97. Basal Ganglia Calcifications Basal ganglia calcifications are a normal and common finding on CT scans. Look at this axial CT scan. Note the 2 bright areas marked by the arrows. These are calcifications and should not be confused with acute hemorrhage, which is also bright on CT scans. 98. Knowledge Check 99. Hypothalamus and Pituitary Gland Whereas the thalamus forms the lateral border of the third ventricle, the hypothalamus forms the floor. The primary function of the hypothalamus is to control the autonomic activity of the body, such as temperature, appetite and sleep. The pituitary gland arises from the hypothalamus. Often called the master gland of the brain, the pituitary controls many of the other glands throughout the body through the substances that it secretes into the bloodstream. It is located in the sella turcica and is attached to the hypothalamus by a small, thin stalk called the infundibulum Pituitary Gland Remember that our sample patient was scanned using an MR T2 FLAIR sequence. If we compare the image from the previous slide to this T1-weighted sagittal view from a different patient, you can see how the pituitary is more visible Brainstem The brainstem attaches the brain to the spinal cord. Although it s a small cluster of tissue, the brainstem is of utmost importance to normal brain function because of the sensory and motor nerve connections it contains. There are 3 primary sections of the brainstem: the midbrain, the pons and the medulla oblongata. Each of these sections is made up of different components.

17 102. Brainstem Scroll through this series of slices from our sample patient. Note the location of the brainstem and its various components. Let s talk about these structures in more detail beginning with the midbrain Midbrain The smallest segment of the brainstem is the midbrain, or mesencephalon. If you look at an axial cross-section image of the midbrain, it looks like the face of a mouse, complete with ears, eyes and even a nose. The image on this slide is slice 11 from our sample patient. Notice how the midbrain resembles a mouse face Midbrain The midbrain is made up of 3 parts: the tectum, the tegmentum, and the cerebral peduncles. The tectum is located along the dorsal aspect of the midbrain and includes the paired superior and inferior colliculi. The superior colliculi are involved with vision, and the inferior colliculi are relay stations for sound. Moving anteriorly from the tectum, we have the cerebral aqueduct, the nose of the mouse. The cerebral aqueduct is a channel for cerebral spinal fluid to move from the third ventricle to the fourth ventricle. Moving anteriorly, we cross the tegmentum, which is Latin for covering. The tegmentum is essentially the tissue between the gray matter surrounding the cerebral aqueduct, or the periaqueductal gray matter, and the base of the peduncle. The red nuclei, which represent the eyes of the mouse, are within the tegmentum. The red nuclei are made up of motor nerve fibers and act as yet another pair of relay stations, sending signals between the cerebellum and both cerebral hemispheres. The midbrain diverges anteriorly into symmetric halves that form the ears of the mouse. The mouse ears are the base of the cerebral peduncle, the basis pedunculi. When moving to the tip of the ear, the first structure in the basis pedunculi is the substantia nigra, which in Latin means black substance. The substantia nigra is a band of dark cells that contains melanin. These cells are involved in the control of movement and, therefore, play a role in disorders such as Parkinson disease. They also are responsible for producing the neurotransmitter dopamine, which contributes to learning and reward behaviors and, consequently, is a factor in addiction. The tip of the mouse ear represents the ventral portion of the basis pedunculi, the pes pedunculi, which contains descending pathways from the cerebral cortex to the spinal cord. By most definitions, the term cerebral peduncles includes all of the midbrain, except the superior and inferior colliculi that make up the tectum Pons The pons is the next portion of the brainstem as we proceed inferiorly toward the spinal cord. The pons is located anterior to the fourth ventricle. It is basically a bridge carrying nerve fibers that connect the cerebellum to the cerebrum. The word pons means bridge in Latin. The pons is best viewed on slice 13 of our sample patient Pons Scroll through this animation to examine the pons.

18 107. Medulla Oblongata The medulla oblongata is the final and most inferior portion of the brainstem. It extends from the pons to the foramen magnum and is divided into symmetric halves by the anterior and posterior median fissures. The medulla oblongata contains all the nerve fibers needed for the brain and spinal cord to communicate with each other. It also contains nerve bundles that regulate respiratory rhythm, heart rate and blood pressure, along with vomiting and the vasomotor centers. The olivary bodies, or simply olives, are a pair of characteristic oval-shaped mounds located on the anterolateral surface of the medulla. They contain the olivary nuclei. Distinctive paramedian elevations of nerve bundles running craniocaudally along the ventral medulla are called the medullary pyramids Medulla Oblongata The medulla oblongata, like the other parts of the midbrain, can be visualized on several slices of our sample patient s MR scan. Scroll through this animation to view the medulla oblongata Cranial Nerves The 12 cranial nerves are the last group of structures we ll discuss in this module. The important aspects of these nerves from a radiological viewpoint are whether the nerves are sensory or motor, where they originate, which muscles they innervate or which sense they transmit, and where the nerves are located Cranial Nerves The cranial nerves are numbered according to their attachment to the brain, starting anteriorly and moving posteriorly: I olfactory, II optic, III oculomotor, IV trochlear, V trigeminal, VI abducens, VII facial, VIII vestibulocochlear, IX glossopharyngeal, X vagus, XI spinal accessory and XII hypoglossal Cranial Nerve Mnemonics It can be challenging to remember all 12 cranial nerves and their order, but there are many mnemonics that can help. A mnemonic device is a memory tool, usually an acronym or phrase, that helps recall certain information. A simple Internet search of the phrase cranial nerve mnemonics returns more than 45 methods, and you can choose the one that works best for you. For the sake of this module, we ll stick to the following mnemonic: Oh, Oh, Oh, To Touch And Feel Very Green Vegetables, AH. This device uses the first letter of the name of each of the cranial nerves to create a phrase in which the first letter of each word matches the first letter of the cranial nerve. Another mnemonic helps recall which nerves are sensory, which are motor and which are both sensory and motor. It reads, Some Say Marry Money, But My Brother Says Big Brains Matter More Cranial Nerve Mnemonics Look at this table to see how these 2 mnemonics work. Let s list the cranial nerve numbers in the first column and the names of the cranial nerves in the second column. Now let s write the mnemonic in the third column. Look at the first letter of the name of each cranial nerve and how the mnemonic is designed to help you recall the name of that nerve.

19 Now let s identify whether the cranial nerve is sensory, motor or both. The second mnemonic appears in the fifth column. Again, notice how the mnemonic can be used to help you recall whether a cranial nerve is sensory, motor or both. Now, let s discuss each of the cranial nerves Cranial Nerve I Cranial nerve I, called the olfactory nerve, is 1 of only 2 cranial nerves that arise from the cerebrum. It is a completely sensory nerve, and it transmits the sense of smell. An easy way to remember these characteristics is to think of an old factory having a bad smell. The paired nerves can be found passing through the olfactory foramina in the cribriform plate of the ethmoid bone Cranial Nerve II The other cranial nerve that arises from the cerebrum is cranial nerve II, the optic nerve. It also is a completely sensory nerve and, as you may have guessed, it transmits the sense of sight. The optic nerve travels in the optic canal from the back of each globe to the optic chiasm, where it joins the contralateral optic nerve, and the nerve fibers partially decussate, or cross. The optic nerves are easily seen on routine CT and MR scans. Some purists believe that the optic nerve isn t really a true nerve because it s surrounded by the 3 meningeal layers the dura, the arachnoid and the pia instead of the cells that typically encase the nerves Cranial Nerve III Cranial nerve III is the oculomotor nerve. Primarily a motor nerve, it carries impulses to the muscles that control eye movement, except for the superior oblique and lateral rectus muscles. It also innervates the levator palpebrae superioris, which raises the eyelid, and the constrictor papillae and ciliary muscles, which adjusts the size of the pupil. The oculomotor nerve travels from the midbrain to the muscles of the eye through the cavernous sinus and the superior orbital fissure Cranial Nerve III On the left is an axial thin-slice T2-weighted image, so the CSF appears white. The image on the right was obtained using an MR pulse sequence known as FIESTA, or fast imaging employing steady state acquisition. This sequence produces thin-section images with the high signal-tonoise ratio necessary to demonstrate tiny structures such as the oculomotor nerve Cranial Nerve IV Cranial nerve IV is the trochlear nerve. This motor nerve innervates the superior oblique muscle of the eye. It travels from the posterior surface of the midbrain, through the cavernous sinus and superior orbital fissure, to the superior oblique muscle. It is the only nerve that arises from the posterior surface of the brainstem Cranial Nerve IV Cranial Nerve IV is labeled in this axial MR image Cranial Nerve V Cranial nerve V, or the trigeminal nerve, is divided into 3 parts: the ophthalmic nerve, the maxillary nerve and the mandibular nerve. These nerves often are referred to as V1, V2 and V3. The nerve s name, trigeminal, literally means 3 twins. The trigeminal nerve is the major