Primary lymphoma isolated to the trigeminal nerve.

included computed tomography (CT), magnetic resonance imaging (MRI) (Figure 1A and B), and cerebrospinal fluid analysis. Medical treatment for trigeminal neuralgia was started, however this proved to be unsuccessful. His pain worsened, and repeat MRI showed an enlarged, non-enhancing lesion at the root entry zone of the trigeminal nerve (Figure 1C). A neoplastic etiology was suspected, and the patient was investigated for metastatic disease. Normal studies included a CT of the neck, chest, abdomen, and pelvis, multiple lumbar punctures, two positron emission tomography (PET) studies, a bone marrow biopsy, and lab and hematological work-up for inflammatory and paraneoplastic causes. Neurosurgical referral was then made for tumor biopsy. Via a retrosigmoid approach the nerve was found to be grossly