Combined Endonasal - Transorbital Approaches to the Skull Base: a Single Stage Minimally Invasive Technique for Anterior Cranial Fossa Pathology

Introduction: Traditional open approaches to the midline anterior skull base are associated with cosmetically and functional risks (i.e., loss of olfaction) that, while tolerated for malignant or extensive tumors, could be avoided for benign/less extensive pathology. Keyhole craniotomies are based anterolaterally where view of the midline skull base is hindered by the orbital roof; while pure endonasal approaches are limited in their lateral access to the skull base. In this study we illustrate that combining transorbital and endonasal techniques can provide circumferential access to the skull base for selected lesions.

Methods: We present an anatomical study and clinical case series on combined endonasal - transorbital approaches. Transorbital approaches consist of either a supraorbital craniotomy (via a eyebrow or eyelid incision) or transconjunctival craniectomy (via a precaruncular incision). Those are performed in combination with an endonasal approach. Anatomical morphometric study was performed in six orbits. The surface area of the skull base exposed via each approach was studied and compared with the exposure provided by the combined approaches. Case series with 12 patients was studied with patient records, operative findings, imaging, and follow-up chart review to determine surgical outcomes and complications.

Results: The combined endonasal transethmoidal - transconjunctival approach was shown to expose the skull base from the cribiform plate at the midline to as lateral as the medial aspect of the orbital roof, and extending back to the planum sphenoidale; with a tight cuneiform corridor. The combined endonasal transethmoidal - supraorbital approach was shown to have a bifurcated corridor, which provides less access to the anterior segment of the orbit but better posterior access and maneuverability at the midline anterior cranial fossa and parasellar regions. (Fig. 1)

Retrospective chart reviews from 2009 to 2015 indicated that 12 patients underwent combined transorbital-endonasal surgery for: esthesioneuroblastoma, encephalocele, Pneumocephalus, Sinonasal Schwannoma, Meningioma Grade I, Mucocele and CSF leak. In all patients, surgery was considered successful (gross total resection/negative margins or no CSF leak recurrence) except one patient, which has subtotal resection. No cosmetic or orbital complications (including corneal abrasion or lacrimal duct injury) were reported.

Conclusion: Transorbital approaches allow access to midline pathology and lateral anterior cranial fossa not accessible endonasally; it further allows direct visualization of dural/intracranial pathology involvement. The combined transorbital-endonasal approach is a two surgeon/four handed technique that allows circumferential access to the anterior cranial fossa from transcranial and transnasal trajectories in a minimally invasive fashion. For select lesions, this technique is an efficient and safe alternative to traditional open approaches (e.g., bifrontal craniotomy).

Fig. 1 Axial CT-scan of an anatomical specimen with the surgical corridor of the combined approaches color-coded. (A) Combined endonasal transethmoidal (green) – and transconjunctival (red) approach. Notice the more midline and cuneiform corridor provided by this combination. (B) Combined endonasal transethmoidal (green) – and supraorbital (blue) approach. This combination does not provide good access to the superomedial orbital region but provides a wider exposure with acces to the orbital apex, lateral orbital wall and parasellar regions.