A Case of Posterior Communicating Artery Aneurysm Accompanied with Infundibular Dilatation Mimicking a Double-Hump Aneurysm.

Posterior communicating artery (PComA) aneurysms are common cerebral aneurysms. In cases of PComA aneurysms accompanied by anatomical variations of PComA, such as hypoplasia, hyperplasia, or infundibular dilatation, it is challenging to completely determine the relationship between the parent artery, daughter arteries, and the aneurysmal neck preoperatively. We present a case of a ruptured PComA aneurysm originating from the PComA, accompanied by infundibular dilatation, which was preoperatively diagnosed as a double-hump PComA aneurysm with hypoplastic or absent PComA, based on computed tomography (CT) angiography images. This case emphasized that CT angiography does not always visualize the entire vasculature. A more meticulous dissection of the retrocarotid space should be performed to confirm the relationship between the parent artery, daughter arteries, and aneurysmal neck, especially when digital subtraction angiography is omitted, and clipping is planned for double-hump PComA aneurysms, wherein the PComA is not clearly depicted on preoperative CT angiography.