Toxoplasmosis
General description
Toxoplasma, an obligate intracellular protozoan parasite, is recognized as a common opportunistic infection affecting the central nervous system (CNS) of AIDS patients. The primary mode of transmission is the fecal-oral route, although hematogenous spread is also possible.
In immune-competent individuals, toxoplasma infection is typically asymptomatic. However, in immune-deficient patients, particularly those with HIV, toxoplasmosis is the most prevalent opportunistic infection. In HIV-infected patients, toxoplasmosis typically manifests when the CD4+ T-cell count decreases to between 50 and 200 cells per microliter.
Abscess with Eccentric target sign
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Caudate nucleus
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Putamen
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Globus pallidus
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Thalamus
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CerebrumCerebral white matterSubcortical white matter
Imaging studies reveal multifocal abscesses predominantly located in the basal ganglia, thalamus, and corticomedullary junction.
CT images display areas of hypo-isoattenuation with adjacent edema and a mass effect.
On MRI, T1WI depicts hypointensity, whereas T2WI and FLAIR sequences exhibit hyperintensity, which may be occasionally inhomogeneous. T2*WI and SWI demonstrate spotty peripheral hypointensity, indicative of microbleeding.
Although seen in less than 30% of cases, the eccentric target sign, a ring enhancement with contrast-enhancing nodules at the margins of the lesion, is highly suggestive of toxoplasmosis.