Ruptured Vertebral-Anterior Spinal Artery Junction Aneurysm Presenting With Diffuse Subarachnoid Hemorrhage: Diagnostic Limitations of CT Angiography (CTA) and the Role of Digital Subtraction Angiography (DSA) in Management-Related Decision-Making

Subarachnoid hemorrhage (SAH) is most commonly caused by rupture of aneurysms arising from the anterior circulation. Aneurysms involving the anterior spinal artery (ASA) are exceptionally rare and pose unique diagnostic and therapeutic challenges due to their small size, deep midline location, and critical role in spinal cord perfusion. We report the case of a 67-year-old female who presented with a sudden thunderclap headache and diffuse SAH centered in the prepontine cistern with intraventricular extension. CT angiography (CTA) demonstrated a subtle vascular irregularity near the left vertebral-ASA junction, but could not definitively characterize the lesion due to posterior fossa artifact. Digital subtraction angiography (DSA) confirmed a 1.5-2 mm ruptured aneurysm arising from the ASA at its junction with the dominant left vertebral artery and demonstrated functional bilateral ASA collateral supply. Given the high risk of spinal cord ischemia with endovascular treatment, conservative management was selected. The patient's condition stabilized under neurocritical care, and she was discharged to rehabilitation with improved neurological function. This report highlights the limitations of CTA for small posterior circulation aneurysms and underscores the essential role of DSA and ASA collateral assessment in guiding individualized management.