rimary CNS lymphoma is the confinement of extranodal lymphoma to the CNS. Classically, lymphomas are divided into Hodgkin's lymphoma and non-Hodgkin's lymphoma, with a primary extranodal presentation in 5% and 30% of cases, respectively. With an increasing incidence in both the immunocompetent and immunocompromised populations, primary CNS lymphoma represents 1% of all lymphomas and as many as 16% of all primary brain tumors [1]. This amplified prevalence makes primary CNS lymphoma an important consideration in the differential diagnosis of brain lesions. This pictorial essay will review the varied CT and MRI appearances of intracranial lymphomas.
A BFig. 13.-35-year-old HIV-positive man with systemic nodular sclerosing Hodgkin's lymphoma who presented with mental status change. Last CD-4 count was more than 1,200 per cubic millimeter with undetectable viral load. Patient did not respond to antitoxoplasmosis treatment and underwent biopsy. A, Axial unenhanced CT image shows hypodense vasogenic edema around subtle hyperdense lesion (arrow) along medial margin of left parietooccipital lobe. B, Axial T2-weighted MR image shows low signal intensity of lesion (arrow). C, Axial T1-weighted contrast-enhanced MR image shows leptomeningeal enhancement (arrows).