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Neuroradiology Case of the Month

May 2001

Clinical Presentation: An 18-year-old female with AML status post autologous bone marrow transplant presented with fever, mental status changes and new onset seizures.

Radiographic findings: Axial T2-weighted image (Fig. 1) showed a mass in the left temporal lobe subcortical white matter with significant surrounding white matter edema. Contrast enhanced T1-weighted image (Fig. 2) showed peripheral ring enhancement. In addition there were small areas of increased focal contrast enhancement in the right occipital lobe white matter.

Diagnosis: Toxoplasmosis

Figure 1, Axial T2-weighted image shows a left temporal lobe mass with surrounding edema (black arrows). Other small lesions are seen in right parietal lobe (white arrows).	Figure 2. Axial contrast T1-weighted image shows nodular and irregular ring enhancement (black arrow). Small enhancing lesions are seen in bilateral cerebral hemispheres (white arrows).

Discussion: Toxoplasmosis lesions are usually located in basal ganglia and at the corticomedullary junction of the cerebral and cerebellar white matter [1-2]. MR shows multiple heterogeneous high-signal foci on T2-weighted image with nodular or peripheral contrast enhancement. Edema and hemorrhages are commonly seen. These characteristics are variable depending on the stage of infection and treatment. Contrast enhancement may be absent in immunocompromised patients [1]. MR spectroscopy is helpful to differentiate toxoplasmosis from lymphoma. Toxoplasmosis lesion shows remarkably high lactate/lipids peak and virtually absence of normal brain metabolites. In contrast, lymphoma shows high choline peak and moderate elevation of lactate/lipids [2]. Perfusion MR may allow differentiation between cerebral lymphoma and toxoplasmosis [3]. Reduced cerebral blood volume in toxoplasmosis lesions is due to a lack of vasculature within the abscess, whereas increased cerebral blood volume in lymphomas is due to hypervascularity in foci of active tumor growth.

Differential Diagnosis: Lymphoma, Progressive multifocal leukoencephalopathy, Cryptococcoma. Tuberculoma in an immunocompromized patients.

References:

1. Dietrich U, et al. MRI of intracranial toxoplasmosis after bone marrow transplantation. Neuroradiology 2000;42:14-18
2. Chang L, et al. Radiologic-Pathologic Correlation: Cerebral toxoplasmosis and lymphoma in AIDS. AJNR Am J Neuroradiol 1995;16:1653-1663
3. Ernst TM, et al. Cerebral toxoplasmosis and lymphoma in AIDS: Perfusion MR imaging experience in 13 patients. Radiology 1998;208:663-669