Anatomic and surgical basis of the sphenoid ridge keyhole approach for cerebral aneurysms

In vascular neurosurgery, the pterional approach has been used primarily for the treatment of a wide variety of diseases (cavernous angiomas, arteriovenous malformations, etc.), and it is used to take advantage of naturally occurring planes and spaces to expose the major structures of the circle of Willis. It provides access to the major part of the anterior circulation aneurysms and those occurring in the upper and most proximal part of the posterior circulation. Conversely, there has been an increasing interest in the so-called minimally invasive procedures or keyhole approaches to treating cerebral aneurysms in specific locations. In this work, we describe a novel keyhole approach that was conceived to achieve the angle of vision and advantages of the classic pterional approach. This surgical approach is based on the anatomic location of the sphenoid ridge and its relationship with the sylvian fissure and basal cisterns. The initial incision is made over the hairline behind the external border of the eye on the side selected. A skin and muscular flap is reflected anteriorly, and a small 3 x 3-cm craniotomy is completed around the external landmarks of the sphenoid ridge. Further extradural drilling is completed down to the anterior clinoid process. The dura is opened in a semilunar manner, and the sylvian fissure is opened completely to reach the sylvian and basal cisterns. Thereafter, the aneurysm is dissected and clipped according to the standard microtechnique of the neurosurgeon. A step-by-step description of the approach is offered in this work to facilitate a clear understanding of it. We recommend this approach for treatment of aneurysms arising at the anterior part of the circle of Willis. It has the advantages of less operative time, fewer days of hospitalization, and similar morbidity and mortality compared with the standard pterional craniotomy (5.7% on our service for nongiant ruptured aneurysms).