High-flow bypass and trapping for ruptured intracranial internal carotid artery dissection in fibromuscular dysplasia: illustrative case.

backgroundRuptured intracranial internal carotid artery dissecting aneurysm (IICDA) occurring in association with fibromuscular dysplasia (FMD) is exceptionally rare, and the optimal treatment strategy remains undefined. OBSERVATIONS: A 43-year-old woman presented with sudden severe headache and was transferred to the authors' hospital 2 days later after developing impaired consciousness. Initial CT revealed a diffuse subarachnoid hemorrhage with right-sided predominance. Digital subtraction angiography demonstrated a "string-of-beads" appearance in the bilateral cervical internal carotid arteries (ICAs), a fusiform vertebral artery aneurysm, and a dissecting aneurysm of the right intracranial ICA, findings consistent with FMD. A high-flow extracranial-intracranial bypass was performed using a radial artery (RA) graft connecting the external carotid artery (ECA) to the middle cerebral artery (MCA) (ECA-RA-MCA), followed by surgical trapping of the affected ICA. The postoperative course was uneventful, and graft patency was confirmed using imaging. At the 3-month follow-up, the patient had no neurological deficits (modified Rankin Scale score 0). LESSONS: Ruptured IICDA associated with FMD is exceptionally rare. This case suggests that high-flow bypass with trapping may be a safe and effective treatment option in carefully selected patients. https://thejns.org/doi/10.3171/CASE26221.