Infundibular dilatations (IFDs) are conical, triangular, or funnel-shaped enlargements of the origin of cerebral arteries (7–25%). They most frequently affect the origin of the posterior communicating artery (PComA) at its junction with the internal carotid artery (ICA). They are considered normal anatomical variants devoid of pathogenic significance, however some IFDs present with time changes similar to the characteristic of saccular aneurysms.

We report the case of a 60 years old female who presented 10 years ago with subarachnoid hemorrhage caused by a left internal carotid artery aneurysm rupture.

At the time of the first admission, carotid angiography had showed a left internal carotid artery aneurysm and a right posterior communicating artery infundibular dilatation. Neck clipping for the left internal carotid artery aneurysm was performed and she was discharged without any neurological deficit. Ten years later, she suffered from a second subarachnoid hemorrhage; carotid angiography demonstrated a right posterior communicating artery aneurysm developed from the previously documented infundibular dilatation with a de novo right anterior choroidal artery aneurysm.

This case is another proof of the small but growing number of examples of infundibula transformation over time, their risk of progression into saccular aneurysms and subsequent rupture.