The Ultimate Skull Base Approach Doesn't Involve Cutting Bone: Quantifying the Relative Benefit of Interfascial Temporalis Dissection

Objective: The pterional approach is the most well-known approach in neurosurgery. The approach, and its variations, provide access to the sylvian fissure, as well as numerous deeper structures within the basal cisterns, such as the circle of Willis, the suprasellar region, and the upper reaches of the posterior fossa. To increase the surgical exposure of this approach, numerous adjunctive ostial skull base maneuvers have been proposed, including orbital and/or zygomatic osteotomies, aggressive sphenoidotomy, and anterior clinoidectomy. One of the easiest ways to increase illumination and working angles, however, does not involve bone: the interfascial temporalis muscle dissection. Our study aimed to quantitate this increase in exposure, and compare its relative benefit to more time-consuming and potentially morbid approaches such as the orbitozygomatic osteotomy.

Methods: To compare the pterional approach and its extensions, sequential dissections were performed on each of 10 sides of 5 fixed, silicone-injected cadaver heads. On each side, a myocutaneous type dissection (pterional-MC), then an interfascial temporalis dissection (pterional-IF), and finally a frontotemporo-orbitozygomatic (FTOZ) approach were performed. The amount of sphenoid drilling, scalp retraction, and brain retraction were standardized in all specimens. In each category, surgical angles were measured on four deep targets: the tip of the anterior clinoid process, the internal carotid artery terminus, the origin of the posterior communicating artery, and the anterior communicating artery. For each deep target, five surgical angles were measured. Anterior–posterior (AP) angles included a medial, mid, and lateral measurement. Medial–lateral (ML) angles included an anterior and mid measurement.

Results: Comparing the interfascial approach to the myocutaneous one, we noted increases in the AP-mid, AP-lateral, and ML-anterior working angles for all deep targets (p < 0.05). The further addition of an orbitozygomatic osteotomy increased almost all the angles, but incrementally less so (p < 0.05). For the origin of the posterior communicating artery target, the addition of the interfascial dissection increased the AP-mid angle 15.3%, the AP-lateral angle 27.4%, and the ML-anterior angle 23.2%. The addition of an FTOZ obtained an additional AP mid-angle of 5.9%, AP-lateral of 7.4%, and ML-anterior of 5.7%. The addition of an interfascial dissection increased the angles to the anterior communicating artery by 23.0% for AP-mid, 27.8% for AP-lateral, and 20.4% for ML-anterior but the addition of an FTOZ only obtained an additional 5.7% for AP-mid, 7.5% for AP-lateral, and 10.3% for ML-anterior.

Conclusion: Our results demonstrate that for several clinically relevant working angles, the interfascial dissection increases the surgical exposure to a large degree. The addition of an orbitozygomatic osteotomy affords a smaller additional benefit. Our findings indicate that a large proportion of the benefit gained from an FTOZ approach is attributable to the treatment of the temporalis muscle, and does not involve the bone work itself. Increased adoption of this easily performed, low-risk, approach during anterolateral craniotomies may obviate the need for more involved skull base drilling in many cases, and can provide benefit in virtually all cases.