Internal carotid artery dorsal wall aneurysm with configurational change: are they all false aneurysms?

Background: Aneurysms arising from nonbranching sites of the ICA, so-called dorsal wall aneurysm, are rare entity, and present as blister type or saccular type. Occasionally configurational changes have been observed on serial cerebral angiography: a small blister-like bulge on ICA wall on initial angiography progressing to a saccular appearance within a few weeks. Such aneurysm showing configurational change has been regarded as a false aneurysm with fragile wall just like blister-type aneurysm, and direct surgical approach has been considered highly risky. Case Description: A 42-year-old woman with a subarachnoid hemorrhage revealed small "blister-like" aneurysm at the medial wall of the ICA on initial angiography. After 12 days, the following angiograms demonstrated increased aneurysmal size and change of shape into a saccular configuration. Direct surgical approach was performed. The aneurysm had a relatively firm neck, and was successfully clipped without intraoperative rupture. The dome of aneurysm was resected after clipping and the histologic examination revealed it as a true aneurysm. Conclusions: This case suggests that all dorsal wall aneurysms with configurational change are not false aneurysms, and that angiographic findings do not always correlate with the nature of the aneurysmal wall; therefore, we should give more credence to direct surgical observation rather than preoperative angiographic findings when considering the most suitable surgical option.