Primary central nervous system lymphoma (PCNSL) is a rare form of extranodal non-Hodgkin’s lymphoma and occurs in both immunocompromised and immunocompetent patient. The percentage of primary CNS lymphoma is 2.4–3% in all brain tumors and 4–6% of all extranodal lymphoma [1]. These tumors can occur in any age group and have a peak incidence between the fifth and seventh decade of life. However, increased incidence has been reported in age group above 60 years in the last two decades. The median patient age is 56 years, and the male-to-female ratio is 3:2.
About 60% of all PCNSLs involve the supratentorial space with the frontal lobe, basal ganglia, and periventricular region commonly involved. Corpus callosum involvement is rare. The posterior fossa and spinal cord are less frequently affected [2]. In immunocompetent patients, 90% PCNSL are diffuse large B cell (DLBCL) type and the remaining 10% are low-grade lymphomas, Burkitt’s lymphomas, or T cell lymphomas [3]. HIV-related PCNSL is typically a large cell lymphoma with immunoblastic and more aggressive features [4]. The presentations of PCNSL in both immunocompromised and immunocompetent patients is similar, with signs of a focal mass lesion in 70% and 61.3% of patients, respectively [5]. Seizures are less common than with other types of brain tumors probably because PCNSL involves predominantly subcortical white matter rather than epileptogenic gray matter. PCNSL patients do not present with B symptoms such as fever, weight loss, or night sweats.
In immunocompetent PCNSL patients, lesions are solitary in 65% of cases and are located in the cerebral hemisphere (38%), thalamus or basal ganglia (16%), corpus callosum (14%), periventricular region (12%), and cerebellum (9%) [6]. HIV-related PCNSL is solitary in 48.6% of cases and is localized to the cerebral cortex in 65%, the periventricular region in 56%, the basal ganglia in 33%, the cerebellum in 7%, and the brainstem in 4% [5].
CEMRI brain is the imaging of choice. These tumors are hypointense on T1-weighted images, isointense to hyperintense on T2-weighted images, and have homogenous dense enhancement on postcontrast images. Peritumoral edema is relatively limited and is less severe than in malignant gliomas and metastasis [7]. In HIV-related PCNSL ring enhancement is often seen [8]. Steroids, radiation and anti-cancer therapy can alter MRI findings and diagnosis may be difficult [9]. The differential diagnosis of PCNSL includes central nervous system gliomas, metastatic tumors, demyelinating disorders, subacute infarcts, and space-occupying lesions due to an infectious etiology.
On histopathological examination, PCNSLs are highly cellular, diffusely growing tumors with no specific pattern. Centrally large areas of geographical necrosis are common and may harbor viable perivascular lymphoma islands. At the periphery an angiocentric infiltration pattern is frequent. The tumor cells are mature B cells with a PAX5-positive, CD19-positive, CD20-positive, CD22-positive, and CD79a-positive phenotypes [10]. Mitotic activity is high and Ki-67 proliferation index usually exceeds 70% or even 90% [11].
Treatment involves surgical excision followed by radiochemotherapy. Gross-total resection of the tumor is typically not possible because of the infiltrative nature of the tumor [12]. High-dose methotrexate-based polychemotherapy is given [7]. Whole brain irradiation may improve outcome, but has the risk of neurotoxicity in elderly patients. Age (> 65 years) is a major negative prognostic factor and is associated with reduced survival [7, 13]. PCNSL has a poor outcome than does systemic DLBCL.
