RAISED INTRACRANIAL PRESSURE AND HERNIATION

Raised intracranial pressure is an increase in mean CSF pressure above 200 mm water with the patient recumbent. It occurs when the volume of brain tissue increases beyond the limit

permitted by compression of veins and displacement of CSF. Most cases are associated with a mass effect, either diffuse, as in generalized brain edema, or focal, as with tumors,

abscesses, or hemorrhages. Because the cranial vault is subdivided by rigid dural folds (the falx and tentorium), a focal expansion of the brain causes it to be displaced in relation to these

partitions. If the expansion is sufficiently severe, a herniation of the brain will occur ( Fig. 28-2 ).

• Subfalcine (cingulate) herniation occurs when unilateral or asymmetric expansion of a cerebral hemisphere displaces the cingulate gyrus under the falx cerebri. This may be

associated with compression of branches of the anterior cerebral artery.

• Transtentorial (uncinate, mesial temporal) herniation occurs when the medial aspect of the temporal lobe is compressed against the free margin of the tentorium cerebelli.

With increasing displacement of the temporal lobe, the third cranial nerve is compromised, resulting in pupillary dilation and impairment of ocular movements on the side of the

lesion. The posterior cerebral artery may also be compressed, resulting in ischemic injury to the territory supplied by that vessel, including the primary visual cortex. When the

extent of herniation is large enough, the contralateral cerebral peduncle may be compressed, resulting in hemiparesis ipsilateral to the side of the herniation; the changes in the

peduncle in this setting are known as Kernohan's notch. Progression of transtentorial herniation is often accompanied by hemorrhagic lesions in the midbrain and pons, termed

secondary brainstem, or Duret, hemorrhages ( Fig. 28-3 ). These linear or flame-shaped lesions usually occur in the midline and paramedian regions and

are believed to be due to tearing of penetrating veins and arteries supplying the upper brainstem.

• Tonsillar herniation refers to displacement of the cerebellar tonsils through the foramen magnum. This pattern of herniation is life-threatening because it causes brainstem

compression and compromises vital respiratory and cardiac centers in the medulla oblongata.

Figure 28-2Major herniations of the brain: subfalcine, transtentorial, and tonsillar. (Adapted from Fishman RA: Brain edema. N Engl J Med 293:706, 1975. Copyright © 1975,

Massachusetts Medical Society. All rights reserved.)

Figure 28-3Duret hemorrhage involving the brainstem at the junction of the pons and midbrain.

Figure 28-4 A, Hydrocephalus. Dilated lateral ventricles seen in a coronal section through the midthalamus. B, Midsagittal plane T1-weighted magnetic resonance image of a child with

communicating hydrocephalus, involving all ventricles. (B, courtesy of Dr. P. Barnes, Stanford University Medical Center, CA.)

Figure 28-5Holoprosencephaly (severe alobar form). View of the dorsal surface showing a lack of separation of cerebral hemispheres, a single ventricle, and fused basal ganglia.

Figure 28-6Agenesis of the corpus callosum. The midsagittal view of the left hemisphere shows the lack of a corpus callosum and cingulate gyrus above the third ventricle.

Figure 28-7Arnold-Chiari malformation. Midsagittal section showing small posterior fossa contents, downward displacement of the cerebellar vermis, and deformity of the medulla

(arrows indicate the approximate level of the foramen magnum).

Figure 28-8Periventricular leukomalacia. Central focus of white matter necrosis with a peripheral rim of mineralized axonal processes (staining blue).

Figure 28-9 A, Multiple contusions involving the inferior surfaces of frontal lobes, anterior temporal lobes, and cerebellum. B, Acute contusions are present in both temporal lobes, with

areas of hemorrhage and tissue disruption. C, Remote contusions are present on the inferior frontal surface of this brain, with a yellow color (associated with the term plaque jaune).

Figure 28-10Epidural hematoma covering a portion of the dura. Multiple small contusions are seen in the temporal lobe. (Courtesy of Dr. Raymond D. Adams, Massachusetts General

Hospital, Boston, MA.)

Figure 28-11Epidural hematoma (left) in which rupture of a meningeal artery, usually associated with a skull fracture, leads to accumulation of arterial blood between the dura and the

skull. In a subdural hematoma (right), damage to bridging veins between the brain and the superior sagittal sinus leads to the accumulation of blood between the dura and the arachnoid.

Figure 28-12 A, Large organizing subdural hematoma attached to the dura. B, Coronal section of the brain showing compression of the hemisphere underlying the hematoma.

Figure 28-13Cerebral infarction. A, At low magnification, it is possible to see the demarcated areas of an acute infarction. In the underlying white matter, the areas of infarction are well

shown by the myelin stain. B, Acute ischemic injury causes diffuse eosinophilia of neurons, which are beginning to shrink. C, Infiltration of a cerebral infarct by neutrophils begins at the

edges of the lesion where vascular supply has remained intact. D, After about 10 days, an area of infarction is characterized by the presence of macrophages and surrounding reactive

gliosis. E, Remote small intracortical infarcts are seen as areas of tissue loss with a small amount of residual gliosis.

Figure 28-14Widespread white matter hemorrhages are characteristic of bone marrow embolization.

Figure 28-15 A, Sections of the brain showing a large, discolored, focally hemorrhagic region in the left middle cerebral artery distribution (hemorrhagic, or red, infarction). B, A

hemorrhagic infarction is present in the inferior temporal lobe of the left side of this brain. C, A bland infarct with punctate hemorrhages, consistent with ischemia-reperfusion injury, is

present in the temporal lobe.

Figure 28-16Old cystic infarct. Destruction of cortex and surrounding gliosis.

Figure 28-17 A, Massive hypertensive hemorrhage rupturing into a lateral ventricle. B, Hypertensive hemorrhage in the pons, with extension to fill the fourth ventricle.

Figure 28-18Common sites of saccular (berry) aneurysms in the circle of Willis.

Figure 28-19 A, View of the base of the brain, dissected to show the circle of Willis with an aneurysm of the anterior cerebral artery (arrow). B, Dissected circle of Willis to show large

aneurysm. C, Section through a saccular aneurysm showing the hyalinized fibrous vessel wall (H & E).

Figure 28-20Lacunar infarcts in the caudate and putamen.

Figure 28-21Pyogenic meningitis. A thick layer of suppurative exudate covers the brain stem and cerebellum and thickens the leptomeninges. (From Golden JA, Louis DN: Images in

clinical medicine: Acute bacterial meningitis. N Engl J Med 333:364, 1994.)

Figure 28-22Frontal abscesses (arrows).

Figure 28-23Characteristic findings of viral meningitis include perivascular cuffs of lymphocytes (A) and microglial nodules (B).

Figure 28-24 A, Herpes encephalitis showing extensive destruction of inferior frontal and anterior temporal lobes. (Courtesy of Dr. T.W. Smith, University of Massachusetts Medical

School, Worcester, MA.) B, Necrotizing inflammatory process characterizes the acute herpes encephalitis.

Figure 28-25The diagnostic histologic finding in rabies is the eosinophilic Negri body, as seen here in a Purkinje cell (arrows).

Figure 28-26HIV encephalitis. Note the microglial nodule and multinucleated giant cells.

Figure 28-27Progressive multifocal leukoencephalopathy. A, Section stained for myelin showing irregular, poorly defined areas of demyelination, which become confluent in places. B,

Enlarged oligodendrocyte nuclei stained for viral antigens surround an area of early myelin loss.

Figure 28-28Cryptococcal infection. A, Whole brain section showing the numerous areas of tissue destruction associated with the spread of organisms in the perivascular spaces. B, At

higher magnification, it is possible to see the cryptococci in the lesions.

Figure 28-29 A, Toxoplasma abscesses in the putamen and thalamus. B, Free tachyzoites demonstrated by immunostaining. C, Toxoplasma pseudocyst with bradyzoites highlighted by

immunostaining.

Figure 28-30Necrotizing amoebic meningoencephalitis involving the cerebellum (organism highlighted by arrow).

Figure 28-31Mechanism and pathology of prion disease. A, Proposed mechanism for the conversion of PrPc through protein-protein interactions. The initiating molecules of PrPsc may

arise through inoculation (as in directly transmitted cases) or through an extremely low-rate spontaneous conformational change. The effect of the mutations in PrP (see B) is to increase

the rate of the conformational change once PrPsc is able to recruit and convert other molecules of PrPc into the abnormal form of the protein. Although the model is drawn with no other

proteins involved, it is possible that other proteins play critical roles in the conversion of Prpc to PrPsc . B, The basic structure of the PrP protein with important sites of mutation (codon

178) and disease-associated polymorphism (codon 129). In normal individuals, codon 178 encodes Asp (D), and codon 129 encodes either Met (M) or Val (V). In some familial forms of

disease, the mutation changes codon 178 to Asn (D178N). When the allele containing the D178N mutation also has a Val at codon 129, the patient develops Creutzfeldt-Jakob disease

(CJD). In contrast, when the D178N allele has Met at codon 129, the clinical disorder is fatal familial insomnia. C, Histology of CJD showing spongiform change in the cerebral cortex.

Inset, High magnification of neuron with vacuoles. D, Cerebellar cortex showing kuru plaques (periodic acid-Schiff [PAS] stain) representing aggregated PrPsc .

Figure 28-32Multiple sclerosis. Section of fresh brain showing brown plaque around occipital horn of the lateral ventricle.

Figure 28-33Multiple sclerosis. A, Unstained regions of demyelination (MS plaques) around the fourth ventricle. (Luxol fast blue PAS stain for myelin). B, Myelin-stained section

shows the sharp edge of a demyelinated plaque and perivascular lymphocytic cuffs. C, The same lesion stained for axons shows relative preservation.

Figure 28-34Alzheimer disease with cortical atrophy most evident on the right, where meninges have been removed. (Courtesy of Dr. E.P. Richardson, Jr., Massachusetts General

Hospital, Boston, MA.)

Figure 28-35Alzheimer disease. A, Neuritic plaque with a rim of dystrophic neurites surrounding an amyloid core. B, Congo red stain of the cerebral cortex showing amyloid deposition

in the blood vessels and the amyloid core of the neuritic plaque (arrow). C, Neurofibrillary tangles (arrowheads) are present within the neurons (H & E). D, Silver stain showing a

neurofibrillary tangle within the neuronal cytoplasm.

Figure 28-36Mechanism of amyloid generation in Alzheimer disease. Amyloid precursor protein (APP) is a transmembrane protein, with potential cleavage sites for three distinct

enzymes (a-, b- and g-secretases) as shown in A. The Ab domain extends from the extracellular side of the protein into the transmembrane domain. When APP is cleaved by a-secretase

(B), subsequent cleavage by g-secretase does not yield Ab. In contrast, cleavage by b-secretase followed by g-secretase (C) results in production of Ab, which can then aggregate and

form fibrils. In either pathway, intramembranous cleavage by g-secretase follows cleavage at a site located closer to the N-terminus of the protein.

TABLE 28-2-- Genetics of Alzheimer Disease

Date: 2016-04-22; view: 734