Primary Central Nervous System Lymphoma of the Posterior Fossa in Immunocompetent Patient: A Case Report and Review of Literature

Context: Primary central nervous system lymphomas (PCNSL) are a rare but very aggressive subtype of extranodal non-Hodgkin lymphomas. They represent only 4% of primary central nervous system lesions and are more common in patients with aggressive non-Hodgkin lymphomas, who are HIV positive. Moreover, PCNSL, usually presents as intraparenchymal supratentorial expansive lesions, while secondary CNS lymphomas tend to present as metastases in the leptomeninges. Although they are more common in immunocompromised patients, their incidence has increased with advancing age. Due to its uniqueness in findings, rarity, and severity of the case, we present an immunocompetent elderly patient with a primary lesion of the posterior fossa. Case report: A 85-year-old female was admitted to the emergency room with incoercible vomiting for 48 hours. Initial clinical examination showed dysmetry, and dysbasia. There was no clinical history compatible with immunosuppression. The initial magnetic resonance imaging revealed two non-enhancing contrast lesions in T1 and hyperintense in T2/Flair in the left caudate nucleus, and at the right cerebellar hemisphere near the fourth ventricle and a third parafalcine lesion with homogenous contrast-enhancing on T1 compatible with an incidental meningioma. PET scan, thyroid and breast ultrasonography, and abdominal MRI were done to rule out metastasis, and all results were negative. The histopathological analysis after a stereotactic biopsy performed on the caudate nucleus lesion confirmed the presence of primary central nervous system lymphoma. Conclusions: The pattern of PCNSL is changing due to aging. Knowing this is indispensable for the correct diagnosis and management.