Acute middle cerebral artery occlusion due to a small internal carotid aneurysm cavity with blood stagnation: illustrative case.

backgroundIn cerebral large vessel occlusion, even when an aneurysm is close to the target vessel, if the aneurysm is relatively small and angiography shows no thrombus within the aneurysm, it is difficult to identify the aneurysm as the embolic source. OBSERVATIONS: A 67-year-old man with a history of two left-sided cerebral infarctions developed a small left-sided cerebral infarction. On hospital day 3, he developed a left M2 occlusion and underwent thrombectomy with retraction of a stent retriever into an aspiration catheter at the proximal end of the thrombus. A red thrombus was retrieved, and M2 recanalization was successfully achieved. Angiography revealed a large partially thrombotic aneurysm with a small cavity with blood stagnation in the left cervical internal carotid artery, which was considered the embolic source. Stent-assisted coil embolization was performed on the aneurysm, and no recurrent cerebral infarction was observed after embolization. LESSONS: In cerebral large vessel occlusion, an aneurysm cavity with blood stagnation may be the embolic source. Using an aspiration catheter alone or retracting a stent retriever into an aspiration catheter could be a useful technique and help to avoid interference between the aneurysm and the stent retriever. https://thejns.org/doi/10.3171/CASE24406.