Minimally Invasive Approaches for Anterior Skull Base Meningiomas: Supraorbital Eyebrow, Endoscopic Endonasal, or a Combination of Both? Anatomical Study and Surgical Application

Background: Minimally invasive accesses to the anterior skull base include the endoscopic endonasal and the supraorbital eyebrow approaches. These are often seen as competing and not alternative or combinatory approaches. For lesions such as meningiomas, drilling of their skull base attachment is important for completeness of resection and to decrease chances of tumor recurrence, in particular in younger patients. The aim of this study is to evaluate the anatomical limitations of each approach when accessing and drilling the anterior skull base, and to propose the combination of both approaches for specific lesions.

Methods: Five injected anatomical specimens were employed to complete a supraorbital approach to the anterior skull base with the aid of the microscope and endoscope. The limitation of the approach was based on the ability to drill the anterior skull base. Five additional injected anatomical specimens were employed to perform an endoscopic endonasal approach (EEA) to the anterior skull base and evaluate its anatomical limitations for anterior skull base drilling. Then, we added a supraorbital approach to complete the visualization of anterior cranial fossa and evaluate the combination of both approaches. After dissection, fine-cut CT scans were performed to better define the limitation of each approach.

Result: The maximal lateral extension of the EEA was accomplished by adding a superomedial orbitotomy to the exposure, which requires removal of the lamina papyracea, gentle dissection and displacement of the periorbita, and resection of the medial aspect of the orbital roof. The maximal lateral extension was then located at the level of the mid-orbit, but this limit was narrower at the level of the orbital apex. The limitation of the supraorbital approach was mostly medial and anterior. The limit for anterior skull base drilling with this approach was defined based on the sphenoethmoidal suture when using the microscope and the posterior aspect of the crista galli when using endoscopic visualization. We propose that for lesions that involve the cribriform plate/crista galli and require skull base drilling, the supraorbital approach alone will not be sufficient because it does not provide enough access or vascularized reconstruction options. Similarly, for lesions that extend beyond the mid orbit or above the orbital apex and require skull base drilling, the EEA will not be sufficient either. In those situations the combination of both approaches will overcome the limitations of each approach while still adhering to minimally invasive but also maximally efficient surgery. We present an illustrative case of an orbital roof meningioma with ethmoidal extension where both approaches were combined to achieve complete tumor resection (Simpson grade 1) and vascularized skull base reconstruction with no complications.

Conclusion: The limitations of the EEA when dealing with the lateral extension of anterior skull base meningiomas, and the limitations of the supraorbital eyebrow approach for skull base drilling and reconstruction, can be overcome by a judicious, anatomically-based combination of both approaches.