Primary Brainstem Angiosarcoma Mimicking Cavernous Malformation

Background: Cerebral angiosarcoma is an extremely rare malignant tumor that originates from vascular endothelial cells of the brain or meninges. Especially, primary brainstem angiosarcoma has not been reported. Case Description: A 64-year-old man presented with left subjective weakness, hypesthesia, and dizziness. Brain imaging showed a multistage hemorrhagic mass in the right dorsal pons, which was initially misdiagnosed as a cavernous malformation. The patient's neurologic status suddenly deteriorated over a few months, and the mass grew rapidly. Surgical resection was performed, and the final pathology showed brainstem angiosarcoma. Conclusions: To our knowledge, this is the first case of brainstem angiosarcoma confirmed by pathology after surgical resection. This report highlights that clinicians need to consider angiosarcoma as part of the differential diagnosis for rare hemorrhagic lesions in the brainstem when both imaging findings and neurologic deterioration indicate rapid progression.