CAT scan of an AIDS patient shows multiple inhomogeneous lesions in the brain, deformation of ventricles and a space occupying lesion in the temporal lobe. The latter lesion has a denser part that appears circular. Compare these X-ray data with the pathologic findings in the next slide.

A coronal section of the brain of another patient with AIDS. Note the circular necrotic lesions mimicking brain tumor or abscesses. The disease may present with epileptic attacks or with a progressive loss of mental functions leading to coma. Relate these clinical features to neuropatholoagy.

Another coronal section of the brain of an AIDS patient with toxoplasmosis. The lesions are more discrete and appear as hemorrhagic foci varying in size and shape.

Perivascular infiltrate of inflammatory cells. Intravascular thrombosis.

Gliosis and aggregates of microorganisms. These tachyzoites measure 3-6 microns. Tachyzoites may infect any cell in the human body. In humans the infestation is usually latent. More than 50% of adults have antibodies to toxoplasma indicative of a previous infection. Only in an immunosuppressed patient there is activation of the latent infection, and thus encephalitis ensues. Tachyzoites appear as bluish dots and are morphologically indistinguishable from other members of the Trypanosoma-Leishmania family.

Toxoplasma cysts filled with numerous bradyzoites. These cysts have developed in "nurse" cells. The cells nurturing the cysts died, and thus, the cysts appear to be located in the extracellular space.

Gross appearance of the herpetic encephalitis. The infection has a predilection for the temporal lobe. Explain why.

An older herpetic lesion shows marked atrophy of the temporal lobe.

Progressive multifocal leukoencephalopathy (PML) tends to occur in the setting of a patient with an immunological deficiency such as AIDS, a lymphoproliferative disorder, or widespread carcinomatosis. The disease is caused by polyomavirus (a subgroup of papovavirus), usually JC virus. Characteristic macroscopic findings are multiple foci of grey to brown discoloration and softening involving white matter.

Cryptococcus meningitis. This slide shows silver impregnated fungi measuring 5-10 microns and showing unequal budding. No hyphae are formed.

Cryptococcus in the cerebrospinal fluid demonstrated with the India ink technique. The yeast capsule is thick and forms a broad hallo impenetrable to the ink. The round fungi are seen in the center of these halloes.

CAT scan of the brain of an AIDS patient shows atrophy of the brain and irregular appearance of the gyri. These findings are nonspecific although indicative of a diffuse destructive encephalitis. HIV has a tendency to infect neuro and microglia cells and cause diffuse damage and destruction of the brain. Dilatation of the ventricles ex vacuo is a secondary event. Symptoms of AIDS encephalopathy vary from one patient to another and include dementia, or neurons and focal neurologic symptoms. Coma develops terminally.

Question for Class Discussion