A Fatal Case of a Ruptured Posterior Communicating Artery Aneurysm in a Patient With Undiagnosed Klippel-Feil Syndrome

Klippel-Feil syndrome (KFS) is a rare congenital disorder characterized by cervical vertebral fusion and often associated with multisystem anomalies. Although primarily skeletal, KFS has been linked to vascular abnormalities, including arterial dissections, agenesis, and aneurysms. We present the case of a 33-year-old previously healthy woman who presented with diffuse subarachnoid hemorrhage. Imaging revealed a ruptured 5.5 mm posterior communicating artery aneurysm arising from the left supraclinoid internal carotid artery, along with congenital cervical vertebral fusion consistent with undiagnosed KFS. The patient underwent emergency craniotomy with clip ligation complicated by intraoperative rupture and cerebral edema, ultimately requiring decompressive hemicraniectomy. Despite maximal surgical and medical management, she progressed to brain death. This case suggests a possible association between KFS and cerebrovascular anomalies and highlights the importance of considering vascular imaging in patients with KFS who present with acute neurological deterioration. Increased awareness of these potential complications may aid in earlier recognition and improved outcomes.