Fig 4. Case 4, Right infundibular dilation at the junction of the internal carotid artery–posterior communicating artery (fetal type), misdiagnosed as an aneurysm and treated surgically, in a 44-year-old woman.

A, 3D MR angiogram shows an aneurysm-like protrusion (large arrow) and a conical bleblike elongation (small arrow).

B, 3D MR cisternogram, coordinated projection as to the 3D MR angiogram in A, shows an infundibular dilation (arrow) with a large posterior communicating artery. PDF (small arrow); CN-III (large arrow); PComA ().

C, Fusion image of the 3D MR angiography/cisternography shows the anatomic relationship of an aneurysm-like complex to a large posterior communicating artery, and indicating not an aneurysm but an infundibular dilation.