Anatomical analysis of intraorbital structures regarding sinus surgery using multiplanar reconstruction of computed tomography scans

Objectives. This study aimed to investigate the anatomy of the intraorbital structures regarding to endoscopic sinus surgery and external frontal sinus surgery analyzing computer tomography (CT) scans. Methods. The CT scans of 100 patients were retrospectively evaluated. The anatomic relationships between the intraorbital structures and paranasal structures were measured using multiplanar reconstruction of the CT scan. Results. The mean distances from the medial orbital floor (MOF) to the intraorbital structures were measured at the depth of the anterior ethmoid (AE), basal lamella (BL), and midportion of posterior ethmoid (PE) in the coronal planes respectively. The mean distances from the MOF to the medial rectus muscle and inferior rectus muscle at the depth of AE were approximately 8 mm and those distances in the BL and PE decreased rapidly. The mean distances from the MOF to the infraorbital nerve at the depth of the AE and BL were approximately more than 10 mm. The mean distances from the vertical axis, which passed through the MOF, to the superior oblique muscle and optic nerve at the depth of the PE were approximately 5 mm medially and 1 mm laterally. In addition, the mean distance from the midline to the trochlea of the superior oblique muscle was approximately 15 mm. Conclusions. Those measurements provide spatial information on the placements of the extraocular muscles within the orbit. The measurements will contribute to the avoidance of orbital complications during sinus surgery.