Anomalies associated with aneurysms of the anterior communicating complex: Microsurgical implications

Aneurysms of the anterior communicating complex are frequently associated with anomalies that, if misdiagnosed or not sufficiently considered, may significantly influence the surgical outcome. A consecutive series of 407 patients with aneurysms of the anterior communicating artery (ACoA) complex - operated on from 1980 to date - has been evaluated in order to recognize important associated vascular anomalies. The most frequent anomalies are represented by agenesis (or hypoplasia) of one supraoptic (A1) tract, fenestration of the anterior communicating artery and presence of 3 distal anterior cerebral (A2) arteries. Hypoplasia of one A1 tract was a rather common observation (147 case = 36%), with no angiographic filling in 12.5% and scant filling in 23.6% of patients with ACoA aneurysms. This anomaly has a practical value, since when the right A1 is hypoplastic a left-sided approach can be a reasonable choice, especially for aneurysms projecting antero-inferiorly or transversely to the right. In order to evaluate the possible risks of a left-sided surgical approach, 69 cases approached from the left were compared with 273 cases approached from the right (all with preop grades I to III, according to Hunt and Hess classification): no difference in good recovery or mortality was observed in the whole series, although slightly worse results were observed after early surgery in patients with a left-sided approach. As regards true anomalies, 16 patients presented with a fenestrated anterior communicating artery; surgical outcome was not influenced by this anomaly. Another 18 patients presented with 3 distal anterior cerebral arteries (ACAs); this anomaly required careful dissection of vessels and meticulous positioning of the clip; postoperative morbidity was slightly increased in these cases. Three patients presented with aneurysms located on a pre-communicating division of the A1 tract (generally at the origin of the Heubner artery), all made a good recovery after surgery. Two patients with ACoA aneurysms presented with an azygous distal anterior cerebral artery, both made a good recovery. Finally, one patient with an unruptured ACoA aneurysm presented with an infero-optic A1 tract, and another presented with an aneurysm located on the left proximal A2 (at the origin of the left fronto-orbital artery); with complete separation of the left and right ACAs: both anomalies are extremely rare, and both patients made a good recovery. It is concluded that knowledge of vascular is very useful when planning surgery for aneurysms of the ACoA complex, since associated anomalies are not infrequent for this aneurysmal location; in the majority of cases, surgical risk is not increased, provided that the anomaly is suspected on angiography and recognized during surgery.