Vascular Lesions

Herniations, by pressing the cerebral arteries against the surrounding structures, produce pale or hemorrhagic infarcts (Fig. 2.20; see also Table 2.7).

Normal Tentorial Notch

FIGURE 2.19

Types of cerebral herniations. A. Anatomic specimen showing the structures in the tentorial opening. Note the relationship between the midbrain, oculomotor nerves, posterior cerebral arteries, uncus, and parahippocampal gyrus. B. Transtentorial herniation of the left uncus and parahippocampal gyrus in an acute subdural hematoma. Note the deep groove around the her-niated gyri caused by the rigid tentorial edge. The midbrain and the aqueduct are compressed and displaced to the right. C1. A transverse band of pallor in the myelin-stained left oculomotor nerve likely corresponds to the site of compression against the tentorial edge. C2. The right oculomotor nerve is normal. D. Right peduncular notch associated with a left temporal mass lesion. Displacement of the midbrain to the right pressed the pedunculus against the tentorial edge, which resulted in a notch (Kernohan's notch). Note also the herniation of the cingular gyrus and compression of the ventricle. E. Subfalcial herniation. Dorsal view of herniated cingular gyrus associated with a frontal mass lesion. F. Cerebellar tonsillar herniation associated with a hemispheric carcinoma metastasis. Note the deep groove around the tonsils caused by their downward thrust through the foramen magnum.

FIGURE 2.19

Types of cerebral herniations. A. Anatomic specimen showing the structures in the tentorial opening. Note the relationship between the midbrain, oculomotor nerves, posterior cerebral arteries, uncus, and parahippocampal gyrus. B. Transtentorial herniation of the left uncus and parahippocampal gyrus in an acute subdural hematoma. Note the deep groove around the her-niated gyri caused by the rigid tentorial edge. The midbrain and the aqueduct are compressed and displaced to the right. C1. A transverse band of pallor in the myelin-stained left oculomotor nerve likely corresponds to the site of compression against the tentorial edge. C2. The right oculomotor nerve is normal. D. Right peduncular notch associated with a left temporal mass lesion. Displacement of the midbrain to the right pressed the pedunculus against the tentorial edge, which resulted in a notch (Kernohan's notch). Note also the herniation of the cingular gyrus and compression of the ventricle. E. Subfalcial herniation. Dorsal view of herniated cingular gyrus associated with a frontal mass lesion. F. Cerebellar tonsillar herniation associated with a hemispheric carcinoma metastasis. Note the deep groove around the tonsils caused by their downward thrust through the foramen magnum.

FIGURE 2.20

Vascular lesions associated with mass lesions and raised intracranial pressure. A. Massive pontine hemorrhage (Duret hemorrhage). B. Occipital hemorrhagic infarct.

FIGURE 2.20

Vascular lesions associated with mass lesions and raised intracranial pressure. A. Massive pontine hemorrhage (Duret hemorrhage). B. Occipital hemorrhagic infarct.

Pontine Hemorrhage

Mesial temporal and occipital infarct results when the herniated hippocampus compresses the posterior cerebral artery against the tentorial edge.

Anterior cerebral artery infarct occurs with the subfalcial herniation of the cingulum, when the artery is pressed against the rigid falx.

Superior cerebellar infarct occurs in upward cere-bellar herniation and results from compression of the artery against the tentorial edge.

Brainstem hemorrhage (Duret hemorrhage) occurs when displacement of the brainstem stretches, angu-lates, or tears the branches of the basilar artery, thus leading to multiple confluent petechial hemorrhages. Hemorrhages also can result from impairment of venous drainage into the vein of Galen.

Pituitary necrosis results from the impairment of circulation in the hypophyseal portal blood vessels.

Bony erosions result from long-standing edema. Common sites are the dorsum sellae and the posterior clinoid process.

CLINICAL MANIFESTATIONS OF INTRACRANIAL EXPANDING MASS LESIONS AND RISING INTRACRANIAL PRESSURE

Intracranial expanding lesions and a rising intracranial pressure produce characteristic symptoms and signs; some provide important diagnostic clues and others warn of a deteriorating and life threatening situation. They are divided into (a) general features, (b) localizing features, and (c) signs of herniations.

General Features

Headaches, variable in nature, present often at night or on awakening. Intermittent at onset, they gradually increase in frequency, severity, and duration. They often are localized to the vicinity of the mass lesion, but with rising intracranial pressure, become more diffuse.

Nausea and vomiting occur with or without headaches and are more common with posterior fossa mass lesions.

Seizures, partial or generalized, may be the presenting symptom and, for months or even years, the only manifestations of a slow-growing mass.

Papilledema is the most important diagnostic sign of increased intracranial pressure, but is not always present. It presents with a gradual decrease of visual acuity, constriction of the visual field, and enlargement of the blind spot.

Alteration in level of alertness, progressing from lethargy and obtundation to stupor and coma, indicates rising intracranial pressure and is usually associated with signs of herniation.

Mental symptoms are manifold; decline of cognitive functions, loss of spontaneity and initiative, affective disorders, behavioral changes, hallucinations and, occasionally, psychotic behavior have been associated with mass lesions. Some relate to rising intracranial pressure and others are reactions of the personality to an impaired cerebral function.

Localizing Features

Neurologic symptoms and signs indicate the location of the lesions.

Psychiatric symptoms of localizing significance are most likely associated with lesions in the frontal lobe and temporomesial region.

A false localizing sign is a hemiparesis on the side of a hemispheric mass lesion, which results from a contralateral peduncular notch associated with hippocam-pal herniation.

Isolated abducens nerve palsy due to displacement of the brainstem and stretching of the nerve roots has no localizing significance.

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