What does a fusiform aneurysm in this location may represent?
A fusiform aneurysm involving the distal vertebral artery with the history of a sudden headache and SAH is compatible with a dissecting aneurysm.
Why an arterial dissection there leads to a SAH?
It happens because the intracranial arteries have thinner tunica media and tunica adventitia compared to the extracranial vessels. When a tear breaches these layers (dissection), there is a little tissue preventing extension into the subarachnoid space.
Procedure and findings: Intubated patient brought from from ICU after EVD insertion. With informed consent.
Right groin approach ( 5-French sheath ) bilateral common carotid, and vertebral artery angiography was performed with 3D acquisition of the left vertebral. A dissecting aneurysm of the V4 segment of the left vertebral artery distal to the left PICA origin. The dissection appears to extend up to the proximal basilar as well. The aneurysm measures 8.9x6.7 mm in dimensions. Both PCOM are prominant with good cross circulation. No other aneurysms, arteriovenous malformation or dAVF present.Haemostasis with 6F angioseal.
Conclusion: Dissecting aneurysm involving the V4 segment of the left vertebral artery with dissection extending to the proximal basilar artery.