J Neurol Surg B Skull Base 2015; 76 - P021
DOI: 10.1055/s-0035-1546649

Expanded Endonasal Approach to the Intraconal Orbit: A Comparative Anatomic Study with and without External Rectus Muscle Displacement

Rounak B. Rawal 1, Lewis J. Overton 1, Ana L. Rodriguez 1, Zainab Farzal 1, Deanna Sasaki-Adams 1, Matthew Ewend 1, Charles S. Ebert 1, Brent A. Senior 1, Adam M. Zanation 1
  • 1University of North Carolina–Chapel Hill Hospitals, North Carolina, United States

Background: The expanded endonasal approach (EEA) has previously been described to access the medial orbit for a variety of pathology; however, intraconal approaches are still novel and evolving. Here, we study inferior rectus and medial rectus displacement via an external approach and the degree of endoscopic access it allows on fresh human cadaveric specimens.

Study Design: This is a comparative anatomic study on fresh human cadavers.

Methods: Endoscopic approaches to the medial and intraconal orbit were performed. Measurements of anterior and medial rectus corridors of the AEA and PEA and extent of optic nerve visualization were performed. Vessel loops were then externally introduced into the sites of medial rectus and inferior rectus attachment to the globe and displaced by an assistant. Inter-rectus distances were then remeasured. Paired Student t-tests were used to compare measurements.

Results: A total of four human cadavers were dissected bilaterally (n = 8). Mean medial rectus length and standard deviation were 17 ± 0.27 mm. Mean optic nerve length and standard deviation were 8.6 ± 0.25 mm. Mean caudal–rostral distance and standard deviation between medial and inferior rectus at the level of the AEA and PEA were 3.5 ± 0.8 and 1.3 ± 0.3 mm (p < 0.0001). After external rectus muscle displacement, mean caudal–rostral distance and standard deviation at the AEA and PEA were 4.9 ± 1.1 and 1.7 ± 0.2 mm (p < 0.0001). Significantly greater changes in access with rectus muscle displacement were afforded at the AEA as compared with at the PEA (1.4 vs. 0.4 mm, p = 0.0047). Video of dissection along with changes in access with rectus muscle displacement is also included.

Conclusion: Greater access to orbital contents is afforded by external rectus muscle displacement. The magnitude of increased access is greater in the anterior orbit as compared with the posterior orbit. This may aid in surgery decision making for planning endoscopic endonasal intraconal surgery.