De novo ruptured intracranial aneurysm associated with cerebral proliferative angiopathy: illustrative case.

BACKGROUND: Cerebral proliferative angiopathy (CPA) is a distinct vascular entity different from arteriovenous malformation but remains exceedingly rare. The authors report a case of subarachnoid hemorrhage (SAH) caused by rupture of a de novo intracranial aneurysm arising in the setting of CPA. OBSERVATIONS: A 47-year-old female presented with headache and was transferred to the emergency department. Head CT revealed SAH (World Federation of Neurosurgical Societies grade III, Fisher group 3). Digital subtraction angiography showed diffuse vascular dilatation and arteriovenous shunting centered on the right middle cerebral artery (MCA). A newly developed aneurysm at the right posterior cerebral artery P1-P2 junction was treated by coil embolization to prevent rebleeding. Postoperatively, SPECT revealed right frontal hypoperfusion, and transcranial Doppler showed elevated flow velocity in the right MCA M1 segment consistent with vasospasm. The patient was discharged to rehabilitation with mild left upper limb paresis and cognitive impairment (modified Rankin Scale score 2). LESSONS: The authors present a rare case of CPA presenting with SAH and discuss the postoperative management of ruptured, flow-related aneurysms. Regular imaging follow-up is crucial to monitor for potential development of de novo aneurysm in CPA. https://thejns.org/doi/10.3171/CASE26216.