Pterional keyhole clipping for unruptured middle cerebral artery aneurysms. Importance of pre-operative planning using three-dimensional CT angiography with osteostomy technique

The pterional keyhole approach was used to clip 55 cases of relatively small unruptured aneurysms of the middle cerebral artery (MCA). Three-dimensional (3D) computed tomography angiography and 3D bone imaging with osteostomy technique were used for the pre-operative planning. The spatial relationship between the aneurysm dome and the sphenoid ridge is particularly important to determine the optimal location of the keyhole. The 55 MCA aneurysms were classified into 3 subgroups based on their relationship to the sphenoid ridge, namely sylvian type (25 cases), infra-sylvian type (22 cases), and supra-sylvian type (8 cases). The pterional keyholes were made according to the subtypes to perform minimally invasive clipping procedures. The optimal size and location of the keyholes were determined in each case. The diameter of the pterional mini-craniectomy was as small as 25 mm. One patient developed temporary mild hemiparesis, and 2 patients suffered from incomplete frontalis muscle weakness. No shaving of scalp hair, drain placement, or anticonvulsive agent administration were required. Most patients were discharged by the 3rd postoperative day without functional neurological deficits. The pterional keyhole approach based on pre-operative imaging allows minimally invasive clipping surgery for unruptured MCA aneurysms. (author)