J Neurol Surg B Skull Base 2015; 76 - P088
DOI: 10.1055/s-0035-1546715

Endoscopic Endonasal Approach to the Optic Canal: Anatomical Considerations and Surgical Relevance

Kumar Abhinav 1, Yancy Acosta 1, Luis Bonilla 1, Wei Hsin Wang 1, Maria Koutourousiou 1, Carl H. Snyderman 1, Paul A. Gardner 1, Juan C. Fernandez-Miranda 1
  • 1University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania, United States

Background: Increasing use of endoscopic endonasal surgery for suprasellar lesions involving the optic canal (OC) has necessitated a better endonasal anatomical definition of the OC. The optic nerve (ON) has been well described previously in terms of four distinct segments including the intracranial, intracanalicular, intraorbital, and intraocular.

Objectives: We defined the osseous OC, as identified transcranially with respect to the endonasal landmarks. The relationship of the ON to the falciform ligament was explored. The technical nuances for safely opening the falciform ligament and the intracanalicular dura endonasally to permit removal of the tumor were investigated.

Methods: A total of 10 fresh human head silicon-injected specimens underwent endoscopic transtuberculum/transplanum approach followed by two-piece orbitozygomatic craniotomy for inspection of 20 OCs and the endonasal–transcranial correlation. After completion of 270-degree endonasal bony decompression of the OC, the dural incision starting at the sella continued superiorly and then anterolaterally across the limbus sphenoidale and anterior cranial fossa.

Results: Endonasally, the osseous OC at approximately 6 mm was equivalent to the length of the lateral opticocarotid recess (LOCR). The ophthalmic artery arose from the supraclinoidal carotid artery at approximately 2.5 mm from the OCs' entrance and was most commonly inferomedial to the intracranial ON. Transcranial correlation of the endonasal dural incision confirmed medial detachment of the falciform ligament and exposure of the preforaminal intracranial segment of the ON.

Conclusion: Using LOCR, distinction of the preforaminal ON, roofed by the falciform ligament from the intracanalicular segment in the osseous OC, preoperatively facilitates the surgical strategy regarding the extent of OC decompression and dural opening. Extensive endonasal decompression of the OC and division of the falciform ligament can be safely performed. Of surgical relevance, we propose that the intracranial segment of the ON should be considered to include both the cisternal and the preforaminal segment, with the latter being roofed by the falciform ligament.