Lateral optico-carotid recess as an anatomical landmark for optimal endoscopic optic nerve decompression.

Background: Transnasal endoscopic decompression of the optic nerve is increasingly gaining acceptance among ear, nose, and throat (ENT) surgeons, however neither strict indications for the procedure nor the precise extent of effective decompression have been firmly established to date. This study aimed to determine the distance between endoscopically visible, anatomical structures within the sphenoid sinus and the posterior (i.e. intracranial) endpoint of decompression. The lateral optico-carotid recess (LOCR) is proposed as a reference for the undertaken measurements.

Methods: The precise localizations of the LOCR and the point at which the optic nerve is covered by bone only for 180° of its circumference were determined using high-resolution computed tomography performed in 30 subjects (60 orbits). Reformed high-resolution computed tomography scans, perpendicular to the optic canal, were used for all measurements.

Results: The point at which optic nerve decompression can be safely terminated was identified in proximity to the medial edge of the LOCR: in all cases, no further than 2.5 mm anterior to this landmark (assigned a negative value) and no further than 1.3 mm posterior (assigned positive values), with a mean of -0.4±1.3 mm. When measured from the orbital apex, the distance ranged from 4.8 to 14.4 mm, with a mean of 8.7±2.5 mm.

Conclusions: The LOCR can be directly discernible by the endoscopic surgeon and identified on the reconstructed high-resolution computed tomography scans, offering a reliable landmark for designating the required extent of decompression. Measurements related to the orbital apex proved less credible, and additionally, this landmark is challenging to identify during surgery.