Surgical Anatomy of the Medial Wall of the Orbit in 14 Human Cadavers

Abstract

Objective The aim of our study is to present the anatomical landmarks to perform an endoscopic endonasal approach to the medial wall of the orbit (EEAMO). Material and Methods We performed 14 complete nasal and orbital endoscopic dissections in 7 adult cadaveric heads. Results The EEAMO provides a surgical corridor between the medial rectus muscle superiorly and the inferior rectus muscle inferiorly .The mean distance between the ethmoidal crest and medial rectus muscle was 1.5 cm (range, 1.3-1.9 cm). The width of the medial rectus muscle was 1.2 cm (range, 1-1.5 cm). The main vascular structure in this retrobulbar space was the ophthalmic artery that crosses over the optic nerve in 86% of the cases. In its intraorbital route, the anterior ethmoidal artery and the ethmoidal nerves were situated inferior to the superior oblique muscle in all cases. The posterior ethmoidal artery was found superior to it. We could identify the inferior division of the oculomotor nerve in this surgical approach. Conclusions The EEAMO allows adequate exposure of the space between the medial rectus muscle and the inferior rectus muscle. The location of the ethmoidal crest of the palatine bone, and its relationship with the medial rectus muscle, is a useful anatomical landmark for this surgical approach.

Keywords: endoscopic sinus surgery; optic nerve; orbital; sinus anatomy.

Fig. 1

(A and B) Muscles of the medial orbital wall in the right nasal cavity. In the figure (B), the orbital fat has been partially removed and the MR medially displaced. IR, inferior rectus; MR, medial rectus; MS, maxillary sinus; SO, superior oblique; SS, sphenoid sinus.

Fig. 2

Relationship between the ethmoidal crest of the palatine bone and the medial rectus muscle in the left nasal cavity. ION, infraorbital nerve; IR, inferior rectus; MR, medial rectus; ON, optic nerve; SO, superior oblique; SR, superior rectus.

Fig. 3

(A and B) Location of the ophthalmic artery between the medial rectus muscle and the inferior rectus muscle in the left nasal cavity. (A) The OA runs superior to the optic nerve. (B) The OA runs inferior to the optic nerve. EB, eyeball; OA, ophthalmic artery; ON, optic nerve; PCA, posterior ciliary arteries.

Fig. 4

The left ophthalmic artery and its medial branches. AEA, anterior ethmoidal artery; MR, medial rectus; OA, ophthalmic artery; PEA, posterior ethmoidal artery; SO, superior oblique; SOA, supraorbital artery.

Fig. 5

Inferior branch of the oculomotor nerve (CN III) in the right nasal cavity. IR, inferior rectus; IIIi, inferior branch of the CN III; IR, inferior rectus; CN, cranial nerve; MR, medial rectus; ON, optic nerve; PCA, posterior ciliary arteries.

Fig. 6

(A and B) Nasociliary nerve and its branches in the right nasal cavity. AEAN, anterior ethmoidal artery and nerve; AEN, anterior ethmoidal nerve; ITN, infratrochlear nerve; MR, medial rectus; NCN, nasociliary nerve; PEN, posterior ethmoidal nerve; SO, superior oblique.

Fig. 7

(A and B) The trochlear nerve (CN IV) between the superior rectus muscle and the oblique superior muscles in the right nasal cavity. In (B), the endoscope is placed between SO and SR. *, IV nerve with two trunks entering the oblique superior muscle; AEA, anterior ethmoidal artery; CN, cranial nerve; MR, medial rectus; PEA, posterior ethmoidal artery; SO, superior oblique; SR, superior rectus.

Fig. 8

The left medial orbital wall divided into three segments: the bulbar space, the retrobulbar space, and the orbital apex. AEA, anterior ethmoidal artery; ON, optic nerve; PEA, posterior ethmoidal artery.