A Rare Presentation of Primary Central Nervous System Lymphoma in an Immunocompetent Patient.

Primary central nervous system lymphoma (PCNSL) is a rare non-Hodgkin's lymphoma (NHL) that can develop in the brain, spinal cord, leptomeninges, and vitreoretinal space. The majority of cases are diffuse large B-cell lymphomas. Risk factors include immune dysfunction, prior Epstein-Barr viral infection, HIV, and a family history of non-Hodgkin's lymphoma. Although the majority of the patients are immunocompromised, PCNSL is still seen in immunocompetent patients. PCNSL has a poor prognosis and a high relapse rate despite its radiosensitive and chemosensitive nature. It is important to recognize and diagnose PCNSL early to improve outcomes. We present a case of PCNSL in an immunocompetent adult with no previously known risk factors. We present a case of a 66-year-old male who presented with a 1.5-week history of right-sided headache and left-sided weakness. After being admitted for further evaluation, he underwent multiple laboratory tests and imaging studies. The CT head indicated ill-defined hypodensities in the pons and left cerebellum. CTA revealed a 1.5 cm outpouching along the medial aspect of the distal left cervical internal carotid artery at the C1-C2 level concerning a pseudoaneurysm. Neurology was consulted, and an MRI of the brain revealed equivocal brain lesions. Neurosurgery was consulted, and the patient underwent an open brain biopsy, which revealed a high likelihood of primary CNS lymphoma based on intraoperative pathology findings. CSF analysis revealed an elevated percentage of lymphocytes, including the presence of atypical lymphocytes as well as elevated oligoclonal bands. Subsequent pathology results confirmed PCNSL. The oncology service was consulted, and the patient was started on corticosteroids and methotrexate for chemotherapy as well as leucovorin. This case represents a rare presentation of PCNSL in which the patient had no known history to support an immunocompromised state. Imaging findings, in this case, were also atypical for a primary CNS lesion as they were mostly equivocal. Furthermore, imaging findings showed diffuse CNS disease rather than an obvious primary lesion as typically demonstrated in the literature. In this case, the open brain biopsy was pivotal in making a timely diagnosis and beginning disease-modifying therapy as early as possible. This case demonstrates the imperative need for clinicians to be aware of varying presentations of PCNSL and possibly consider pursuing a definitive diagnosis with biopsy when the differential includes PCNSL but remains broad after advanced imaging.