Page 180 - AIDSBK23C

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also appear in the meninges or beneath the pia mater on gyral surfaces. Histologic patterns
include ventriculitis, necrotizing vasculitis (which may be extensive), and microglial nodules.
Large violaceous intranuclear and small basophilic intracytoplasmic inclusions can be present in
ependymal cells, astrocytes, or even neurons. However, CMV inclusions can be difficult to find,
even in the most common feature of microglial nodules.[418,756,774]

TOXOPLASMA GONDII.-- Toxoplasmosis is the most common etiology for focal brain
lesions in AIDS, and it occurs in 3% to 40% of AIDS patients, most often in the advanced stages
of HIV infection. The prevalence of toxoplasmosis seen at autopsy has been decreasing with the
use of prophylaxis, and now appears in <10% of cases.[758] In most cases, toxoplasmosis is
probably the result of reactivation of latent infection, since IgM antibodies are lacking.
Toxoplasmosis involving the brain is probably the result of hematogenous dissemination from
other organs, since the CNS lesions are typically multiple.[746]
Toxoplasmosis of the brain can be a clinical presumptive diagnosis to define AIDS using
the following CDC criteria:[392]

• Recent onset of a focal neurologic abnormality consistent with intracranial disease or a
reduced level of consciousness; AND
• Evidence by brain imaging (computed tomography or nuclear magnetic resonance) of a
lesion having a mass effect or the radiologic appearance of which is enhanced by injection of
contrast media; AND
• Serum antibody to toxoplasmosis or successful response to therapy for toxoplasmosis.

Clinically, the most common presenting symptoms are fever, headache, and confusion or
altered consciousness. These non-specific findings occur in about half of cases, while specific
neurologic deficits occur in about two-thirds of patients with CNS toxoplasmosis. The most
common focal neurologic signs include hemiparesis, ataxia, and cranial nerve palsies. Seizures
are less frequent.[746,775,776]
The lesions of toxoplasmosis on computed tomographic (CT) scans may resemble the
findings of either abscesses or neoplasms. Unenhanced CT findings include multiple lesions or
focal lesions that appear as isodense masses compared to grey matter, but hyperdense if
hemorrhagic. Lesions appear most often in basal ganglia, thalamus, and corticomedullary
junctions. With contrast-enhanced CT imaging the lesions are usually ring-enhancing with
surrounding vasogenic edema and mass effect.[759] The radiologic lesions progress as
enhancing nodules, and they may be distinguished from lymphoma by presence of hemorrhage
as well as their increased number and decreased size. On T2-weighted MR images, the majority
of the lesions are iso- or hypointense surrounded by high signal intensity vasogenic edema.
Cerebral toxoplasmosis appears as hypointense on T1 weighted scans; there is moderate to
intense ring enhancement with contrast enhancement on MRI. Thallium-201(TI-201) brain
spectral emission computed tomography (SPECT) has been utilized to differentiate
toxoplasmosis from lymphoma. In patients with toxoplasmosis, no uptake of TI-201 is identified
in CNS lesions in contrast to lymphoma, where an abnormal increased uptake is usually
found.[738,657,752, 777]
Diagnosis of toxoplasmosis cannot be routinely made by CSF examination, and serum
antitoxoplasma antibodies, though usually present, may be absent. However, if Toxoplasma