Common and Uncommon Features of Central Nervous System Lymphoma on Traditional and Advanced Imaging Modalities

Central nervous system (CNS) lymphoma can occur in isolation as a primary CNS neoplasm or can show systemic lymphoma involvement. Primary CNS lymphomas in patients who are immunocompetent are typically hyperattenuated on CT and iso- to hypointense relative to gray matter on T1- and T2-weighted images. On postcontrast scans, strong homogeneous enhancement is common. Most primary CNS lymphomas contact a CSF surface (either the ventricular ependyma or the pia). Advanced MR imaging may help to differentiate primary CNS lymphomas from other brain lesions. Typical primary CNS lymphomas are highly cellular tumors without necrosis; the lesions are hyperintense on diffusion-weighted images and hypointense on apparent diffusion coefficient maps. The relative cerebral blood volume ratios of primary CNS lymphomas are much lower than those of high-grade gliomas and metastases. On MR spectroscopy, elevated choline as well as a decreased N-acetylaspartate peak and high lipid peak are observed. Unlike high-grade gliomas, hemorrhages and calcifications are rare. Unusual imaging features of primary CNS lymphomas include patchy, streaky, or no enhancement; hemorrhage; necrosis; and calcifications. In patients who are immunocompromised, primary CNS lymphomas show central necrosis and peripheral enhancement. Systemic lymphomas can involve the CNS: two-thirds of patients with secondary CNS lymphoma present with leptomeningeal spread, and one-third present with parenchymal disease. An accurate diagnosis of CNS lymphoma is crucial for proper management and prognosis in both patients who are immunocompetent and those patients who are immunocompromised. The imaging features described herein may allow earlier recognition of CNS lymphoma and thus facilitate optimal treatment.

Learning Objective: Recognize common and uncommon types of primary CNS lymphomas in patients who are immunocompetent and patients who are immunocompromised as well as variation in the appearance of secondary CNS lymphoma on MRI and to describe characteristic imaging findings by using advanced imaging techniques.