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
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.