MR of primary CNS lymphoma in immunologically normal patients.

PURPOSE To describe the MR findings of primary CNS lymphoma.

METHODS MR scans of 20 patients with histologically proved primary CNS lymphoma were reviewed. We evaluated the size, multiplicity, signal intensities, and enhancement characteristics of the lesions. We divided the lesions into an enhancing area referred to as Zone 1 and abnormal signal surrounding this, referred to as Zone 2.

RESULTS Primary CNS lymphoma presented as solitary enhancing lesions in 40% of the patients and multiple lesions in 40%. Thirty-three separate lesions were visible: 58% abutted the ventricular system, 76% showed a homogenous enhancement pattern, and 79% showed marked enhancement. In 64% of the lesions, Zone 1 and Zone 2 showed different signal intensities on T1-weighted images.

CONCLUSIONS Primary CNS lymphoma usually presents as solitary or multiple dense homogenous enhancing lesions that abut an ependymal surface. These lesions can be divided into an enhancing area and an area of surrounding abnormal signal. These two areas often have different signal intensities on unenhanced T2-weighted images. These findings are sufficiently suggestive of the diagnosis of primary CNS lymphoma that a needle biopsy be performed based on these findings and appropriate therapy can then be instituted.