Comparison of Endoscopic Transethmoidal and Prelacrimal Approaches for Exposure of the Medial Intraconal Space: A Cadaveric Study

Introduction: Both the transethmoidal and prelacrimal approaches can be utilized to access the medial intraconal space (MIS). The purposes of this study were to compare the advantages and drawbacks of each approach for exposure, and to explore the appropriate indications for management of lesions at varying locations within the MIS.

Methods: Six injected cadaveric specimens were dissected using an endonasal approach. For each specimen, a transethmoidal approach was performed on one side, while a prelacrimal approach on the contralateral side. The exposure provided by these two approaches to various zones within the MIS as well as structures included was assessed.

Results: The MIS was divided into three zones based on horizontal lines crossing the superior and inferior borders of medial rectus muscle (MRM). Zone 1 was defined as the area above the superior border of MRM, zone 2 defined as the area between the MRM and optic nerve, and zone 3 as the area below the inferior border of MRM. Both approaches provided adequate exposure of zones 2 and 3; however, the prelacrimal approach provided direct exposure of the posterosuperior aspect of zone 2 without retraction of MRM, while retraction of MRM was unavoidable using a transethmoidal approach. Access to zone 1 was best achieved through the corridor between superior oblique and medial rectus muscles.

Conclusion: Subdivision of the MIS into three zones will be beneficial in selecting the optimal approach for lesions restricted to each specific zone. Both a transethmoidal or prelacrimal approach could access zones 2 and 3; however, the prelacriaml approach is more suitable for direct exposure of the posterosuperior aspect of zone 2 given the reduced need for retraction of the MRM. For lesions restricted to zone 1, the transethmoidal approach is best indicated.