Retromedullary Hemangioblastoma Mimicking a Posterior Inferior Cerebellar Artery Aneurysm: Case Report and Literature Review

Background: Hemangioblastomas (HBMs) are benign vascular neoplasms that most commonly arise within the cerebellum. Although other vascular lesions should be considered in the differential diagnosis, HBMs rarely resemble aneurysms on neuroimaging and only 1 case of a cerebellar HBM mimicking a posterior fossa aneurysm has been reported. Here we describe a retromedullary HBM that masqueraded as a distal posterior inferior cerebellar artery (PICA) medullary branch aneurysm. Case Description: A 63-year-old asymptomatic male was incidentally diagnosed with an unruptured 3-mm left PICA aneurysm via computed tomography angiography during a workup for carotid stenosis. Two years later, the presumed aneurysm enlarged to 6.5 mm and prompted elective treatment. Endovascular treatment was unsuccessful, and the patient was immediately transitioned to a craniotomy for aneurysm clipping. After microsurgical dissection, the lesion was visualized on the posterior medullary surface with several small arterial feeders extending from the brainstem into the aneurysm dome, but no major parent vessel was observed. Because a clip could not be safely applied to these small vessels, they were instead coagulated and the lesion was completely resected. Final pathology revealed hemangioblastoma (World Health Organization grade I). Conclusions: To our knowledge, this is the second case of HBM mimicking a PICA aneurysm. Given the rarity of PICA medullary branch aneurysms and their highly symptomatic nature, other etiologies, especially HBM, should be strongly considered when an apparent distal PICA aneurysm is diagnosed in an asymptomatic patient. If the lesion is unamenable to endovascular treatment, there should be high suspicion for HBM and subsequent craniotomy should be pursued.