Middle cerebral artery anatomical variations and aneurysms: a retrospective study based on computed tomography angiography findings

Background: Anatomical variations of the middle cerebral artery (MCA) are an important clinical issue, due to high prevalence of intracranial aneurysms. Anatomical variations of vessels can lead to higher shear stress, which is thought to be the main factor leading to aneurysm formation and consequently to higher prevalence of aneurysms. The aim of this study was to evaluate anatomy of the MCA; to classify MCA aneurysms using computed tomography angiography and to correlate anatomical variations of MCA and circle of Willis with prevalence of MCA aneurysms. Materials and methods: Two hundred and fifty patients without MCA aneurysms and 100 patients with unruptured MCA aneurysms were qualified for the study, with exclusion of patients after MCA clipping. Four aspects of MCA anatomy were evaluated: division point, its relation to the genu, distance to M1 division and the genu and domination of post-division trunks. Results: Middle cerebral artery bifurcation was found in 86.2% and trifurcation in 13.8% of the cases. 78.4% of MCAs divided before the genu, 19.2% in the genu and 2.4% after the genu. Upper branch domination was seen in 26%, lower branch in 25.4%, middle branch in 4% and no domination in 44.6% of the cases. In the study group 116 aneurysms were found. 86.2% of the aneurysms were located in M1 division point, 6.9% in M2 segment, 3.4% near lenticulostriatae arteries and 3.4% near early cortical branches. The only anatomical variation, which had significantly higher prevalence in patients with left MCA aneurysms, was domination of upper post-division trunk of MCA. No other statistically significant differences in circle of Willis and MCA variations were found between patients with aneurysms and without them. Conclusions: The most common configuration of MCA is bifurcation before the genu with no dominating post-division trunk. Incidence of MCA aneurysms is not correlated with anatomical variations of MCA and the circle of Willis.