Analysis of superiorly projecting anterior communicating artery aneurysms: anatomy, techniques, and outcome. A proposed classification system.

Superiorly projecting (SP) anterior communicating artery (AComA) aneurysms are typically described as a homogenous group. Clinically and microsurgically, these aneurysms vary in multiple important characteristics. We propose a microsurgical classification system for these complex aneurysms and review its implications regarding presentation, microsurgical techniques, and outcome. This retrospective analysis reviews patients undergoing clipping of SP AComA aneurysms (2005-2013). The classification system is based on the virtual plane created by the A2 segments and its relationship to the aneurysm. Aneurysm type was assessed by intraoperative images and videos. Type 1 is defined by bisection of the dome by the virtual plane. Type 2 is defined by dome projection posterior to this plane. Sagittal rotation of the plane defines type 3. We analyzed clinical presentation, morphology, angiographic characteristics, operative technique, and outcome relative to the classification types. There were 44 SP AComA aneurysms. 3D angiographic images predicted classification type in 83%. Type 1 presented more often with SAH (95.5%, p = 0.0046). There was no statistically significant difference between the types regarding patient demographics or aneurysm characteristics. In type 2, fenestrated clips were used frequently (87.5% p= 0.0016), and there was higher rate of intraoperative rupture (37.5%). Although there was no statistically significant difference between the types in respect to HH grade upon presentation, patients with type 2 aneurysms experienced higher rates of poor GOS (50%). The proposed classification system for SP AComA aneurysms has implications regarding surgical planning, micro-dissection, clipping, and outcome. Type 2 aneurysms carry significant surgical risk.