Bow Hunter's syndrome on a persistent first intersegmental artery course in extreme old age: A case report.

Background: Bow Hunter's syndrome (BHS) is positional vertebrobasilar ischemia caused by dynamic vertebral artery compromise during head rotation, usually attributed to degenerative compression at C1-2 and typically presenting in midlife. Very elderly cases are seldom recognized. Case Description: A 92-year-old woman presented with a right posterior inferior cerebellar artery infarct. Despite empirical anticoagulation for suspected cardioembolism, she developed recurrent infarcts confined to multiple bilateral posterior circulation territories on day 121. Rotation-provoked duplex ultrasonography demonstrated loss of end-diastolic flow in the right vertebral artery on leftward rotation with preserved flow in neutral and rightward positions. Computed tomography angiography revealed the absence of the right C1 transverse foramen and a persistent first intersegmental artery (PFIA) coursing beneath the C1 posterior arch. Rotational digital subtraction angiography confirmed focal kinking with stenosis at this segment on left rotation. BHS was diagnosed based on the PFIA course and dynamic rotation-dependent stenosis. Because the recurrence pattern and dynamic imaging findings were more consistent with a positional vertebral artery mechanism than with cardioembolism, anticoagulation was discontinued, and aspirin was selected for secondary prevention. A cervical collar was prescribed to restrict rotation. At the 1-year follow-up, the patient remained recurrence-free with preserved functional independence (modified Rankin Scale score, 2). Conclusion: This case broadens the recognized age spectrum of BHS and demonstrates that PFIA can serve as a non-osteophytic substrate for rotational vertebral artery compromise. Dynamic multimodal imaging is essential to establish causality, and clinicians should consider BHS in recurrent posterior circulation-limited ischemic events regardless of age.