Fig. 4

a and b Final magnetic resonance imaging (MRI) of the brain. Follow-up MRI performed 5 months after symptom onset demonstrated complete regression of the previously documented confluent white matter lesions on the axial T2-weighted (3 mm) image (a) and the contrast enhancement in the T1-weighted (3 mm) image after contrast application (b). At the site of the earlier biopsy, a small liquor isointense parenchymal defect with a T2-weighted hypointense hemosiderin rim and residual contrast enhancement of the biopsy cavity was seen in the right frontal lobe (a; arrow)