Imaging description

Primary CNS lymphoma (PCNSL), a malignant brain neoplasm composed of B lymphocytes, occurs only in the CNS in most cases, in contrast to secondary involvement of CNS by systemic lymphoma, in immunocompromised patients with a history of prior infection with Epstein–Barr virus, and occasionally in immunocompetent patients [1]. As brain does not have lymphoid tissue or lymphatic circulation, the site of origin is something of a mystery [1].

Typical PCNSL presents as a solitary or multiple solid mass(es) in the periventricular regions and corpus callosum with avid and homogeneous enhancement, decreased T2 signal, and decreased water diffusivity secondary to increased cellularity with a variable degree of surrounding vasogenic edema [2]. On CT, PCNSL, unlike many other masses, shows hyperattenuation (Fig. 29.1). Deviation from this classic imaging appearance is common, however, particularly in severely immunocompromised patients, and non-enhancing, heterogeneously enhancing, or ring-enhancing lesions present a diagnostic challenge (Fig. 29.2).

Interestingly, PCNSL, unlike most malignant masses, shows decreased rCBV in perfusion imaging, which may be very helpful in differential diagnosis (Fig. 29.3) [3]. They are also seen in subependymal locations with diffuse post-contrast enhancement. When the CNS is secondarily affected due to systemic lymphoma, the imaging findings include dural-based enhancing masses (Fig. 29.4), leptomeningeal and cranial nerve enhancement, pituitary infudibular involvement, and subependymal/intraventricular enhancing lesions (Fig. 29.5) [3].