METHODS: Cerebral diagnostic digital subtraction angiography (DSA) data from our institution between 2002 and 2004 were analyzed retrospectively. The patients were divided into aneurysm and control groups. All patients who had a brain tumor, arteriovenous malformation, arteriovenous fistula or aneurysms other than AComAA were excluded from the study. From 182 patients studied, 75 had AComAA. The control group included 107 patients without any vascular pathology.

RESULTS: The incidence of A1 segment hypoplasia/aplasia was 41.33% in patients with AComAA and 10.28% in control group. In the aneurysm group, right A1 hypoplasia and right A1 aplasia were established in 12% of the patients. Left A1 hypoplasia was seen in 9.33% and left A1 aplasia in 8% of the patients. In the control group, the most frequently observed anomaly was right A1 hypoplasia at 7.48%. Right A1 aplasia, left A1 hypoplasia and left A1 aplasia were found at the same frequency of 0.93%.

CONCLUSION: A1 segment hypoplasia/aplasia plays an important role in occurrence of AcomAAs. In the literature, the incidence of A1 hypoplasia/aplasia in AcomAAs ranges between 50% and 80%. In our series, we found a lower value than previous series at 41.33%. This may be related to the genetic features of Turkish population and the hypoplasia criteria we employed. Keywords : Anterior communicating artery, Aneurysm, A1 hypoplasia, A1 aplasia