Book Review And Study Questions For Chapter 1 & 2

Areas 3,1,2 collectively represent the primary somatosensory cortex. Area 4 is the primary somatomotor cortex, area 17 the primary visual cortex, and area 22 the primary auditory cortex. Area 40 is in the supramarginal gyrus, a large part of which is called the Wernicke area.(p.14)

The trochlear nerve exits the posterior (dorsal)aspect of the brainstem just caudal to the inferior colliculus and passes around the lateral aspect of the midbrain in the ambient cistern, en route to its exit from the skull via the superior orbital fissure. The abducens nerve exits at the caudal edge of
the pons in line with the preolivary fissure, and the hypoglossal exits from the medulla via this fissure. The trigeminal nerve exits the lateral aspect of the pons, and the vestibulocochlear nerve exits at the most lateral aspect of the pons-medulla junction.(p.32–33,44)

As they descend in the dural sac from their origin from the spinal cord to their exit at their respective intervertebral foramen, the anterior and posterior roots form the caudaequina. The conus medullaris is the most caudal end of the spinal cord, and the filum terminale internum is the strand of pia that extends from the conus caudally to attach to the inneraspect of the dural sac at about S2.The denticulate ligament anchors the spinal cord laterally to the inner surface of the Dural sac, and the filum terminale externum anchors the Dural sac caudally to the inner aspect of the coccyx.(p.12,52–53)

The primary somatomotor cortex consists of the pre-central gyrus and the anterior paracentral gyrus; area 4 is found in these structures. Areas 3,1,and 2 are the primary somatosensory cortex; areas 5 and 7 make up the superior parietal lobule and the precuneus; and area 6 is located rostral to area 4.Portions of area 6 in the caudal region of the middle frontalgyrus are the frontal eye field.(p.14)

The hypoglossal nerve exits the medulla via the preolivary sulcus of the medulla immediately (and laterally) adjacent to the pyramid. The abducens nerve exits in line with the preolivary sulcus, but, at the caudal edge of the pons, and the trigeminal nerve exits the lateral aspect of the pons. The vagus nerve exits the lateral aspect of the medulla via the postolivarysulcus, and the facial nerve in line with this sulcus, but at thepons-medulla junction.(p.24,25)

The limbic lobe, consisting primarily of the cingulate gyrus and the parahippocampal gyrus, is located on the most medial aspect of the hemisphere; the cingulate gyrus is located immediately adjacent to the corpus callosum. None of the other lobes of the cerebral cortex borders directly on the corpus callosum.(p.28,30)

The inferior frontal gyrus consists of the pars orbital-is (Brodmann area 47),pars triangularis (area 45),and parsopercularis (area 44).A lesion located primarily in areas 44 and45 in the dominant hemisphere will result in a nonfluent(Broca) aphasia. The supramarginal (area 40) and angular (area39) gyri represent what is called the Wernicke area, and the middle frontal gyrus contains areas 6 and 8.The lateral one-third of the precentral gyrus is the face area of the somatomo-tor cortex.(p.14,18)

Cerebrospinal fluid and other fluids appear black inT1-weighted MRI images. Consequently, the ventricles, and more obvious parts of the subarachnoid space, appear black. Changes in ventricular shape (i.e., enlargement, midline shift),or obliterated sulci, or even subarachnoid space, most likely represent a potentially serious clinical issue.(p.3–4,63)

The tonsil of the cerebellum is found on the caudal and inferior aspect of the cerebellar hemisphere, adjacent to the midline and immediately posterior (dorsal) to the medulla. The cisterna magna is located in this area. Sudden tonsillar herniation may compress the medulla and damage respiratory and cardiac centers resulting in sudden death. The tonsil herniates downward through the foramen magnum. Consequently, another part of the brainstem is directly affected.(p.36–37)

The quadrigeminal artery is the primary blood sup-ply to the superior and inferior colliculi: this vessel originates from P1
.The geniculate bodies receive their blood supply from the thalamogeniculate arteries, and the pineal and habenula from the posterior medial choroidal artery. The superior cerebellar peduncle receives its blood supply via the medial branch of the superior cerebellar artery, and branches of the cerebral circle (of Willis) serve the mammillary bodies.(p.33,35)

The primary auditory cortex is Brodmann area 41.Areas 3,1,and 2 and area 17 are, respectively, the primary somatosensory and visual cortices. Areas 3940 collectively form the inferior parietal lobule; lesions of this portion of the cerebral cortex give rise to a Wernicke (receptive or fluent)aphasia. Area 45 is the pars triangularis of the inferior frontal lobe; lesions in this cortical region give rise to a Broca (expressive or nonfluent) aphasia.(p.14)

In most cases (85%–100%),the labyrinthine artery, also called the internal auditory (or acoustic) artery, originates from the anterior inferior cerebellar artery. It enters the internal acoustic meatus, serves bone and dura of the canal, the nerves of the canal, and vestibular and cochlear structures. In a few cases (15% or less),this artery originates from the basilarartery. None of the other choices gives rise to vessels that serve the inner ear.(p.25)

The cerebral aqueduct is about 1.5–2.0 mm in diameter, and connects the third ventricle with the fourth ventricle. When this part of the ventricular system appears in a sagittal MRI, the plane of the scan is at the midline. Neither the inter-ventricular foramen nor the superior colliculus are on the mid-line. Both the interpeduncular fossa and the corpus callosumare on the midline, but extend off the midline well beyond the width of the cerebral aqueduct.(p.28,30–31)

A CT is a fast method, does not require sedation of young patients, and shows bone fractures and acute intracranial blood in detail. MRI (T1- and T2-weighted) does not show acute blood or bone fracture to advantage, takes much longer to do, and may require sedation in a child. Enhanced MRI is uniquely useful for tumors, and PET is useful in identifying metabolic activity of brain tissue, not anatomic detail.(p.2–4)

The long and short gyri (gyri longi et breves) are components of the insular lobe. This lobe is located deep to the lateral sulcus, has a central sulcus that separates the short gyri(rostral to this sulcus) from the long gyri (caudal to this sulcus).The cortex of the insular lobe is separated from the adjacentfrontal, parietal, and temporal opercula by the circular sulcus of the insula. None of the other lobes has gyri that are specifically named long and short gyri.(p.38–39)

Numbness on the face, resulting from a lesion in the cerebral cortex, indicates a lesion in the lateral one-third of the postcentral gyrus (face area of the somatosensory cortex).The anterior paracentral gyrus and the precentral gyrus are somatomotor areas of the cerebral cortex. The upper extremity is rep-resented in the middle one-third of the postcentral gyrus and the lower extremity is represented in the posterior paracentralgyrus.(p.14)

The lingual gyrus is the lower bank of the calcarinesulcus; the upper (cuneus) and lower banks of this sulcus are the location of the primary visual cortex. The precuneus is the medial aspect of the parietal lobe, and the angular gyrus is a portion of the inferior parietal lobule on the lateral aspect of the hemisphere. The cingulate and parahippocampal gyri are located on the medial aspect of the hemisphere and are parts of the limbic lobe.(p.14,15,28–30

The uncus is a small elevation at the rostral and medial aspect of the parahippocampal gyrus adjacent to the crus cerebri of the midbrain. In addition to the catastrophic effect of decerebration, herniation of the uncus may also affectcorticospinal and corticonuclear (corticobulbar) fibers in the crus cerebri and the root of the oculomotor nerve. None of the other areas of the forebrain listed as choices is related to uncalherniation.(p.20,22,24)

The primary fissure is the deepest fissure in the cerebellum and it separates the anterior lobe from the posterior lobe and extends from the vermis to the lateral cerebellar margin. The posterolateral fissure is located between the flocculon-odular lobe and the posterior lobe. The horizontal, secondary, and posterior superior fissures are all located within the posterior lobe.(p.36–37)

The optic tract lies immediately on the surface of the crus cerebri, a relationship frequently seen in MRI. The fact that this patient has a right-sided weakness of the extremities specifies that the lesion is in the left crus cerebri. The bilateral visual deficits correlate with damage to the left optic tract. Lesions of the left basilar pons and pyramid would result in aright-sided weakness but no visual deficits. A lesion in the right optic nerve would result in blindness in that eye but no weak-ness of the extremities.(p.26)

The body is represented in the somatomotor cortex(precentral gyrus, anterior paracentral gyrus) in the following pattern: the face in about the lateral one-third of the precentral gyrus above the lateral sulcus; the hand and upper extremity in about its middle third; and the trunk and hip in about its medial third. The lower extremity and foot are represented in the anterior paracentral gyrus. Caudal portions of the middle frontal gyrus are the location of the frontal eye field.(p.14)

The gyrus rectus is located on the inferior and medial aspect of the frontal lobe. It is separated from the orbital gyriby the olfactory sulcus in which the olfactory bulb and tract islocated. None of the other lobes has a direct relationship to the gyrus rectus.(p.20,22)

Clipping the P3 segment proximal to the aneurysm would block all blood flow to targets distal to this point. Distal portions of the posterior cerebral artery (the P4 segment) serve the primary visual cortex. Somatosensory, somatomotor, and auditory regions of the cerebral cortex are served by terminal branches of the middle cerebral artery (M4 in the case of motor and sensory,M3/M4 in the case of auditory).Blindness in one eye would result from a lesion rostral to the optic chiasm; in the case of a vascular cause, this may relate to damage to the ophthalmic branch of the internal carotid.(p.21,29)

A lesion in area 44 (the pars opercularis) that spreads will affect the lower portions of the precentral gyrus in which the face is represented. This will result in weakness offacial muscles, accompanied by other cranial nerve deficits. Thecortical areas for hearing and vision are far separated from area44.Also,a lesion in the primary auditory cortex will not result in a hearing loss in one ear. The hand area of the sensory cortex and the upper extremity area of the motor cortex are not adjacent to Brodmann area 44.(p.14,18)

The rostral edge of the striae medullares (of the fourth ventricle) is regarded as the border between the pontine and medullary portions of the fourth ventricle. These fibers pass from the median fissure in the floor of the ventricle later-ally into the lateral recess, where they arch up into the cerebellum. The facial colliculus and median eminence are located in the floor of the pontine portion of the ventricle, and the vagal and hypoglossal trigones are found in the medial floor of the medullary portion of the fourth ventricle.(p.32,34)

The callosomarginal artery, a branch of the anterior cerebral artery, serves the medial aspect of the superior frontal gyrus and that portion of this gyrus on the superior and lateral aspects of the hemisphere.M4 segments of the middle cerebral artery serve the lateral aspects of the hemisphere;
P4 segments of the posterior cerebral artery serve the medial aspects of the hemisphere caudal to the parietoccipital sulcus, and the angular artery (an M4 branch) serves the angular gyrus of the inferior parietal lobule. The lenticulostriate arteries are branches of M1 that serve internal structures of the hemisphere.(p.19,21,25,29,39)

The deep middle cerebral vein is located on the insular cortex and, by joining with the anterior cerebral vein, forms the basal vein of Rosenthal. The superficial middle cerebral vein is located on the lateral aspect of the hemisphere in the vicinity of the lateral sulcus, arches around the temporal lobe and joins the cavernous sinus. The vein of Labbé drains the lateral aspect of the hemisphere into the transverse sinus.(p.19,21,39)

Lenticulostriate arteries, also called the lateral striate arteries, originate from the M1 segment of the middle cerebral artery and serve much of the lenticular nucleus and adjacent parts of the internal capsule.A1 branches serve the anterior hypothalamus and optic chiasm, and M2 branches serve the insular cortex. The P1 and P2 segments give rise to many small perforating branches and to the thalamoperforating and quadrigeminal arteries (P1),medial and lateral posteriorchoroidal arteries, and the thalamogeniculate artery (P2).(p.21,23,25,29)

Cerebrospinal fluid in the ventricles, and through-out the subarachnoid space, appears very white in T2-weightedMRI images. Structures located in, or traversing the subarachnoid space (such as vessels or cranial nerve roots, including the oculomotor nerve) appear grey to black against a white back-ground.(p.2–5)

The P3 segment lies along the orientation of, and adjacent to, the parahippocampal gyrus as this part of the posterior cerebral artery courses around the midbrain. Branches of the P3 segment serve the inferior surface of the temporal lobe, which includes much of the laterally adjacent occipitotemporalgyri. The lingual gyrus and the cuneus are in the territory of the P4 segment and the orbital gyri are served by branches of the anterior and middle cerebral arteries. The superior temporal gyrus is served by M4 branches of the inferior trunk of the middle cerebral artery.(p.21,29)

Patients who experience rupture of an intracranial aneurysm frequently complain of an intense, sudden headache(“the most horrible headache I have ever had”).Acute blood in the subarachnoid space will appear white to very white on CT. This will contrast with the medium grey of the brain and the black of cerebrospinal fluid (CSF) in the ventricles. The degree of white may vary somewhat, based on the relative concentration of blood, from very white (concentrated blood) to white(mostly blood, some CSF),to very light grey (mixture of blood and CSF).(p.2–4)

Recent studies on humans clearly suggest that the frontal eye field is located primarily in area 6 in the caudal aspect of the middle frontal gyrus. Areas 3,1,2 are collectively the primary somatosensory cortex and area 4 is the primary somatomotor cortex. Areas 5 7 collectively constitute the superior parietal lobule while areas 18 19 represent visual cortical regions that border on the primary visual cortex.(p.14)

The M4 segments of the middle cerebral artery serve the lateral aspect of the cerebral hemisphere. The named M4 vessels that serve the pre- and postcentral gyri (hemorrhage into approximately the lower two-thirds of these gyri explain the motor and sensory deficits) are the precentral branches(prerolandic),central branches (Rolandic branches),and anterior parietal branches. The M2 segment serves the insular cortex, and the M3 segment serves the inner surface of the frontal, parietal, and temporal opercula. The A1 segment serves hypo-thalamic structures, the subcallosal and septal areas, and adjacent structures.P4 serves the medial aspect of the occipital lobe(visual cortex).(p.19,25,39)

The superficial middle cerebral vein is located on the surface of the cerebral hemisphere in the immediate vicinity of the lateral sulcus and, of the choices, is the most likely candidate. The deep middle cerebral vein is located on the surface of the insular lobe. The inferior sagittal sinus primarily drains the medial aspect of the hemisphere immediately superior to the corpus callosum. The internal cerebral vein (to the great cerebral vein) drains the internal parts of the hemisphere; the ophthalmic vein connects the orbit with the cavernoussinus; and the superior petrosal sinus connects the cavernoussinus with the sigmoid sinus at its junction with the transversesinus.(p.19,29,39)

The P4 segments of the posterior cerebral artery consist of the parietooccipital and calcarine branches; the latter being located in the calcarine sulcus and a primary blood sup-ply to the primary visual cortex.M3 and M4 segments of the middle cerebral are located, respectively, on the inner aspect of the frontal, parietal, and temporal opercula and on the lateral aspect of the cerebral hemisphere. The P2 segment of the posterior cerebral artery is located just distal to the posterior communicating–posterior cerebral intersection and gives rise to medial and lateral posterior choroidal and to thalamogeniculate arteries. The A1 segment is located between the internal arotid and anterior communicating artery and gives rise to branches that serve anterior hypothalamic structures, septalareas, and the optic chiasm.(p.14,25)

In this patient, the meningioma is located in the falxcerebri and is impinging on the anterior paracentral gyrus correlating with her motor deficit. The lower extremity is represented in the anterior paracentral gyrus (somatomotor) and in the posterior paracentral gyrus (somatosensory).The precentral gyrus contains the motor representation for the face (later-al part) and the trunk and hip (medial part).The postcentralgyrus is part of the somatosensory cortex.(p.14)