CNS Lymphoma

CNS Lymphoma

CT demonstrates the tumor masses involving the deep gray matter structures, the periventricular white matter, and the corpus callosum; they appear homogeneously isodense to moderately hyperdense (reflecting dense packing of small tumor cells with a high nucleus-to-cytoplasm ratio), have relatively ill-defined margins, and demonstrate diffuse strong homogeneous contrast enhancement.

Peritumoral edema is less extensive than that seen in association with primary gliomas and metastases of similar size.
Central necrosis with peripheral ringlike contrast enhancement is uncommon in immunocompetent patients but is noted more frequently and involves wider areas with larger lesions in immunocompromised patients.


Extension along the ventricular walls with ependymal contrast enhancement and leptomeningeal tumor spread with hyperdensity in and contrast enhancement of the cisterns and sulci are common late findings.

On MRI, the deeply seated tumor nodules exhibit a variable signal intensity pattern. Most often, the tumors are homogeneously isointense to gray matter on both T1- and T2-weighted images, findings that are similar to those for other small cell hypercellular tumors. However, some lesions may exhibit marked T2 hyperintensity. Almost all primary CNS Lymphomas demonstrate intense contrast enhancement after intravenous administration of gadolinium.

In immunocompromised patients, this enhancement is often ringlike (reflecting central necrosis) and associated with extensive peritumoral edema, and the clinical and radiologic presentation can simulate that of toxoplasmosis, a common occurrence in patients with AIDS. The differential diagnosis favors toxoplasmosis if there is associated hemorrhage, whereas the presence of subependymal extension with contrast enhancement of the ventricular walls favors lymphoma. In such circumstances, a short trial of anti-Toxoplasma therapy followed by evaluation of the clinical and imaging response may be sufficient to avoid invasive biopsy.

Leptomeningeal seeding occurs in up to 60% of patients with primary CNS Lymphoma, generally late in the course of the disease. Although malignant cells may be readily detected on CSF cytology, detection of subarachnoid tumor spread on imaging studies has been problematic. Imaging verification of leptomeningeal neoplasm, which is visible as parallel linear streaklike contrast enhancement, may be more easily and reliably detected on FLAIR and T1-weighted postgadolinium MRI than on postcontrast CT.

Ref : Haaga, AJNR.