Rapidly fatal encephalitis associated with atypical lymphoid proliferations of the basal ganglia subsequent to aneurysmal subarachnoid hemorrhage.

Rapidly fatal encephalitis associated with atypical lymphoid proliferations after intracranial aneurysm rupture has not been reported. Here, we describe a 52-year-old female who presented to the emergency department with a severe headache. Imaging demonstrated aneurysmal subarachnoid hemorrhage due to a ruptured left posterior inferior cerebellar artery aneurysm, which was treated with endovascular embolization and subsequent external ventricular drain. She recovered without neurologic sequelae by day seven; however, five weeks later she represented with a severe headache associated with nausea and fever. Initial repeat imaging was unremarkable. She deteriorated quickly and was empirically treated for meningitis despite negative cerebrospinal fluid studies. Magnetic resonance imaging revealed diffuse cerebral edema within the basal ganglia and thalamus. Biopsy of the caudate nuclei revealed atypical lymphoid proliferations. She was treated accordingly with no significant improvement. This case highlights the necessity for a better understanding of the etiology, chronology, and natural history of atypical lymphoid proliferations.