Background: Repeat angiography will identify vascular pathology in approximately 10% of cases following angiogram-negative subarachnoid hemorrhage (anSAH), but small atypical aneurysms of the basilar artery are very uncommon.
Objective: To report a case series of delayed appearance of nontraumatic basilar artery small atypical aneurysms.
Methods: IRB approval was obtained for this retrospective case series and patient consent was waived.
Results: Herein we report three cases of spontaneous anSAH, all of whom had a negative digital subtraction angiogram (DSA) on admission and all of whom had appearance of a small atypical aneurysms of the upper basilar trunk/apex on follow-up imaging (two during the initial admission and one in a delayed fashion). All three patients were ultimately treated with flow diversion (although one patient underwent attempted coiling that was abandoned due to inability to catheterize the aneurysm).
Conclusion: This report highlights the importance of a repeat DSA in cases of anSAH as well as the importance of scrutinizing the basilar trunk for these very small atypical aneurysms that may go unnoticed.
Keywords: Angiogram-negative subarachnoid hemorrhage; flow diversion; perimesencephalic SAH; pseudoaneurysm.