Microvascular surgical anatomy of the vertebrobasilar junction

OBJECTIVE: We examined the pertinent microvascular anatomy of 28 formalin-fixed brains to develop anatomic guidelines for aneurysm surgery in the region of the vertebrobasilar junction. METHODS: Using a surgical microscope, the outer diameters were observed for the following main arteries: vertebral, basilar, posteroinferior cerebellar, and anteroinferior cerebellar. The number of lower brain stem perforating arteries was examined in relation to their course. The distance between the arteries and their perforators was measured with respect to anatomic landmarks. RESULTS: The anatomy of the main arteries was characteristically variable, whereas the anatomy of the perforators was constant, particularly in terms of their numbers and points of penetration into the brain substance, The four major points of entry were the lateral medullary area just caudal to the posterior olivary sulcus, the posterior olivary sulcus, the small lateral fossa at the superior olivary groove, and the foramen cecum. Each of these areas coincides with the origin of common vertebrobasilar aneurysms. CONCLUSION: The anatomy of the main arteries was variable. In contrast, the perforators penetrated the adjoining brain stem at specific locations, regardless of the caliber of the main artery. Despite a small vertebral artery or its major branches, perforators penetrating the brain are significant and may effect the outcome of aneurysm surgery or endovascular procedures.