A classification of unruptured middle cerebral artery bifurcation aneurysms that can help in choice of clipping technique

Middle cerebral artery (MCA) aneurysms comprise 20-25 % of all intracranial aneurysms. The majority of middle cerebral artery aneurysms are treated by microsurgical clipping. Most of the classifications of aneurysms at present are based on size, location or pathology which are effective for the description but are less useful in preoperative planning and also in deciding on the technique or type of clip application. The aim of our study was to examine the morphological features of unruptured MCA bifurcation aneurysms which influence the techniques of clipping of these aneurysms and to attempt to subclassify unruptured middle cerebral artery aneurysms based on their preoperative 3D CTA and intraoperative characteristics so as to help in the intraoperative choice of technique and clip application, respectively. Preoperative 3D CT angiography and intraoperative images along with the record of technique and type of clips used for 141 unruptured MCA aneurysms operated at our center were studied retrospectively. Unruptured MCA bifurcation aneurysms could be subclassified into 5 types based on the similarities in their morphological features which influenced the techniques of clipping as recorded from their preoperative 3D CTA and intraoperative view. These types and the distinctive feature of each type are described. The various techniques of clipping are discussed based on these subgroups. The groups outlined make possible the establishment of a common technical approach to clipping within the groups. This classification, based on preoperative 3D CTA and intraoperative morphological features of the aneurysm and parent vessels, helps in the intraoperative choice of technique and type of clip application to tackle these lesions.