Surgical treatment for vertebral artery–posterior inferior cerebellar artery aneurysms: special reference to the importance of the cerebellomedullary fissure dissection

Abstract

Object The cerebellomedullary fissure (CMF) is a space between the cerebellum and the medulla oblongata, which often adhere to each other. The purpose of the present study was to demonstrate the importance of the unilateral CMF dissection for clipping vertebral artery (VA)–posterior inferior cerebellar artery (PICA) aneurysms. Methods Five adult cadaveric specimens were studied after colored silicone was infused into the arteries and veins. The microsurgical anatomy of the CMF and the trans-CMF approach for VA-PICA aneurysm surgery were examined in stepwise dissections. In addition, 6 patients underwent surgery for VA-PICA saccular aneurysms (2 ruptured and 4 unruptured aneurysms) via posterolateral approaches, with wide opening of the unilateral CMF to obtain good visualization and a wide working space in the lateral part of the cerebellomedullary cistern. Clinical data including neurological and radiological findings and patient outcomes were analyzed in all 6 cases. Results In all cases, the aneurysm was successfully clipped and no permanent neurological deficits remained. The wide opening of the unilateral CMF on the lesion side made it possible to retract the inferolateral part of the cerebellum easily, provided a wide operative field in the cerebellomedullary cistern, and enabled successful clip placement without difficulty. Conclusions For safe and effective VA-PICA aneurysm surgery, it is very important to dissect the CMF on the lesion side as well as to remove the lateral part of the foramen magnum. Direct clip placement is very safe and useful in cases involving VA-PICA aneurysms.