Basilar artery blister aneurysm presenting with subarachnoid hemorrhage: management challenges in the context of basilar artery duplication

Blood blister-like aneurysms (BBAs) are rare, fragile vascular lesions most commonly arising from non-branching segments of the internal carotid artery. Basilar artery BBAs are exceptionally uncommon and present significant diagnostic and management challenges. We report the case of a woman in her late 50s who presented with sudden-onset occipital headache, neck stiffness, and subarachnoid haemorrhage. Digital subtraction angiography identified a 3 mm blister-like aneurysm in the basilar artery, considered the presumed culprit lesion, along with an incidental basilar artery fenestration. Endovascular flow-diversion was recommended; however, the patient declined intervention after informed counselling and was managed conservatively with intensive neurocritical monitoring. The patient recovered without residual neurological deficit. This case highlights the diagnostic overlap between aneurysmal and perimesencephalic subarachnoid haemorrhage, the importance of careful vascular imaging, and the management challenges posed by rare posterior circulation BBAs and associated vascular variants.