Non-enhancing relapse of a primary CNS lymphoma with multiple diffusion-restricted lesions.

Primary CNS lymphoma (PCNSL) and its variant primary intraocular lymphoma (PIOL) are rare forms of extranodal non-Hodgkin's lymphoma confined to the CNS including the retina and the optical nerve; histologically, most cases are diffuse large B cell lymphomas. PCNSL in immunocompetent patients display typical radiological features on MRI, i.e. intensely and homogeneously enhancing lesions with moderate edema. Here, we report a 52-year-old male with a history of a PIOL and two consecutive intracerebral relapses who presented with dysarthria, dysphagia, and gait ataxia. Gadolinium-enhanced T1 scans were unremarkable but multiple lesions with restricted water diffusivity were seen on diffusion-weighted imaging. Relapse of his PCNSL was secured histologically only on autopsy. The possible etiology of the diffusion-restricted lesions is discussed.