Characteristics of aneurysms of the internal carotid artery bifurcation

Background. Arterial bifurcations are sites of maximal hemodynamic stress, where cerebral aneurysms commonly develop. However, in our experience with endovascular treatment for aneurysms of the internal carotid artery (ICA) bifurcation, we often experienced that the aneurysmal neck did not necessarily exist only at the ICA bifurcation (ICBi). In this study, we have retrospectively evaluated characteristics of aneurysms at the ICBi. Methods. Ten ICBi aneurysms in 10 consecutive patients were studied retrospectively. The size of the aneurysms, the angles formed between the ICA and the anterior cerebral artery (ACA) and middle cerebral artery (MCA), and the diameter of the ICA, ACA and MCA were measured. Furthermore, to study the relationship between the location of the aneurysmal neck and the bifurcation of the ICA, the distance between the midline of the aneurysmal neck and of the ICA was measured. Results. The average aneurysm size was 6.3 +/- 3.2 mm and the average neck was 3.1 +/- 1.2 mm. The average ICA-ACA angle was 57.3 +/- 16.5 degrees, and the average ICA-MCA angle was 128.9 +/- 24.1 degrees. The average diameters of the ICA, ACA and MCA were 2.9 +/- 0.5 mm, 1.9 +/- 0.4 mm and 2.5 +/- 0.4 mm, respectively. The average distance between the midline of the aneurysmal neck and the ICA was 1.6 +/- 0.6 mm, and all aneurysmal necks of the ICBi arose from the side of the ACA. Conclusion. ICBi aneurysms were deviated to the side of the A1 segment of the ACA, where the artery might suffer higher hemodynamic stress.