Endoscopic endonasal approach of the medial intraconal space: CT analysis of the anatomic relation between paranasal structures and orbital contents.

OBJECTIVE

This study aimed to investigate the anatomy of the optic nerve (ON), extraocular muscles (EOMs), and paranasal structures with regard to an endoscopic endonasal approach to the orbit using multiplanar reconstruction of computed tomographic (CT) scans.

METHODS

The CT scans of 125 patients were retrospectively evaluated. The anatomic relationships between the ON, EOMs, and medial orbital floor (MOF) were measured on a coronal plane using multiplanar reconstruction of the CT scan.

RESULTS

The mean distances from MOF to medial rectus (MR) and inferior rectus (IR) muscles and distance from MR to IR at the depth of the basal lamella (BL) and midportion of posterior ethmoid (PE) were measured on the coronal planes, respectively. The mean distances at the depth of PE were approximately less than 2 mm and half of those were at the depth of BL. The mean distances from ON to MOF, lamina papyracea, and EOMs at the depth of BL, PE, and sphenoid sinus anterior wall were measured, respectively. The distances from the ON to surrounding structures at the depth of PE were approximately half of those at the depth of BL and the distances from the ON to surrounding structures at the depth of sphenoid sinus anterior wall were less than 2 mm except the distance from the ON to MOF.

CONCLUSIONS

The MOF and EOMs could be the most important and safe anatomic landmarks for an endoscopic approach to the orbit. These results could be used as a reference to minimize ON and EOM injury.