It Is Not Always Metastasis: A Case Report of a Primary Nervous System Anaplastic Large Cell Lymphoma and the Relevance of Brain Biopsy

Primary central nervous system lymphoma (PCNSL) is an uncommon, extranodal non-Hodgkin lymphoma confined to the brain, spinal cord, leptomeninges, or eyes. Most cases are diffuse large B-cell lymphomas; anaplastic large cell lymphoma (ALCL) in the central nervous system (CNS) is exceptional. We report an immunocompetent 63-year-old man with 3 months of intermittent bilateral pulsatile headaches who developed a focal seizure that secondarily generalized. He was started on levetiracetam for a first-time seizure and discharged. Outpatient magnetic resonance imaging (MRI) subsequently revealed a brain mass, prompting referral to our centre. On admission, he was hemodynamically stable; laboratory evaluation showed moderate lymphopenia and mild hyperphosphatemia. Brain MRI demonstrated an irregular extra-axial lesion in the left inferior frontal gyrus with punctate susceptibility foci and extensive vasogenic oedema involving adjacent frontal, insular, and temporal regions. The radiological impression favoured metastasis, and surgical resection was undertaken to obtain tissue and relieve mass effect. Histopathology and immunohistochemistry confirmed primary CNS ALCL, and a bone-marrow biopsy with CD30 immunostaining showed no systemic involvement. Postoperatively, new dysarthria and right hemiparesis developed. Two weeks later, high-dose methotrexate plus cytarabine was initiated, with neurological improvement. Twenty days after chemotherapy, he re-presented with fever, hypotension, and altered mental status. Computed tomography (CT) showed no new intracranial findings, but pancytopenia and cultures positive for carbapenem-resistant <i>Citrobacter freundii</i> were identified, and he died of septic shock. This case illustrates that CNS ALCL can radiographically mimic metastatic disease, underscores the necessity of tissue diagnosis, and highlights the competing imperatives of timely intensive chemotherapy and rigorous infection surveillance, particularly for multidrug-resistant organisms in older adults with PCNSL.