Clinical and Radiologic Diagnosis of Toxoplasmosis
In the immunocompetent individuals, toxoplasmosis causes a self-limited flu-like illness.
However, in the immunocompromised patient, there is fulminant infection with significant
morbidity and mortality. Toxoplasmosis is the most common focal neurologic lesion in the
AIDS population. Multiple ring-enhancing lesions are the most common imaging finding
(Figs. 15A, B, and C). The lesions vary in size and demonstrate surrounding edema. The lesions
are hypodense to isodense on nonenhanced CT. With IV contrast administration, rim
enhancement is present and can be either thin and smooth or solid and nodular. The lesions
are hypointense on nonenhanced T1-weighted imaging and typically hyperintense on
T2-weighted imaging, although this is variable. (28,33)
Mimics of Brain Abscess, CNS Tuberculosis, and Toxoplasmosis
Brain Tumor
Necrotic brain tumors, both primary and metastatic, may also present as ring-enhancing
parenchymal lesions. Unlike an abscess, which typically has smooth margins, a tumor
classically demonstrates thick, nodular rim enhancement. The lesion may be multi-loculated
and complex. The entities can further be differentiated via diffusion-weighted imaging, in
Figure 15 (A) Axial CT image of the brain in a 34-year-old immunocompromised male demonstrates a 3-cm area
of low attenuation in the left cerebellar hemisphere (arrow) with associated mass effect on the fourth ventricle and
acute hydrocephalus. (B) Axial T1-weighted MR image with gadolinium demonstrates peripheral ring enhance-
ment. (C) Coronal T1-weighted gadolinium-enhanced MR image from the same patient demonstrates a second
lesion in the right cerebellar hemisphere (curved arrow), in this patient with toxoplasmosis.
88 Luongo et al.