Evolution from an infundibulum of the posterior communicating artery to a saccular aneurysm

An infrequent case of a de novo aneurysm formation originating from an infundibulum at the origin of the posterior communicating artery (PcomA) is presented. The aneurysm developed within 7 years in a patient who initially presented with subarachnoid hemorrhage (SAH) from a saccular aneurysm of the vertebral artery.

A 43-year-old female patient was admitted to our hospital on 16th June 2000 after an acute onset of massive occipital headache. A computed tomography (CT) scan showed a subarachnoid hemorrhage (SAH) around the brainstem and 4-vessel angiography revealed an aneurysm originating from the V4 segment of the right vertebral artery (VA) as the cause of the SAH. A small aneurysm at the basilar artery (BA)/superior cerebellar artery (SCA) bifurcation was also found. Injection of the left internal carotid artery (ICA) showed a diffuse enlargement at the origin of the left PcomA, which at this time was considered to be a so-called infundibulum. The VA aneurysm was treated by coil occlusion. Follow-up digital subtraction angiography (DSA) in 2005 showed a de novo aneurysm formation at the VA junction, again treated by coil occlusion. The PcomA infundibulum at the left ICA was not examined. Follow-up angiography performed in 2007 revealed a saccular de novo aneurysm of the left ICA arising from the origin of the left PcomA with a maximum diameter of 12 mm. Coil occlusion of the PcomA aneurysm was subsequently carried out.

Infundibular widening of cerebral arteries can develop into true aneurysms. Mid-term and long-term follow-up MRI (e.g., in yearly intervals) is advised for infundibula with a diameter of 3 mm or more. In patients with other aneurysm(s), with a documented de novo aneurysm formation or with a familial occurrence of aneurysms, the risk of evolution of an infundibulum to a saccular aneurysm may be increased and follow-up should be even more stringent.