Evolving cerebrovascular pathology in fibromuscular dysplasia leading to aneurysmal subarachnoid hemorrhage.

Fibromuscular dysplasia (FMD) is a rare, nonatherosclerotic vascular disorder characterized by arterial stenosis, aneurysm formation, dissection, and tortuosity. It predominantly affects women and commonly involves the renal and internal carotid arteries (ICA). While classically associated with renovascular hypertension, cerebrovascular involvement may cause headache, neck pain, or, rarely, intracranial aneurysm and subarachnoid hemorrhage (SAH). We report a case of progressive FMD in which 3 sequential imaging findings drove the diagnostic course: an initial cervical ICA string-of-beads appearance on computed tomography angiography (CTA) leading to the diagnosis of FMD; subsequent intracranial multifocal arterial narrowing and vasospasm on repeat CTA raising suspicion for occult SAH; and digital subtraction angiography (DSA) confirming a ruptured aneurysm at the right superior cerebellar artery-posterior cerebral artery (SCA-PCA) bifurcation. This case highlights the progressive nature of cerebrovascular FMD and the critical role of repeat imaging and multidisciplinary collaboration in establishing the diagnosis.