Anatomy of lacrimal sac fossa affecting success rate in endoscopic and external dacryocystorhinostomy surgery in Mongolians.

To study the affect of anatomical variance of lacrimal sac fossa on dacryocystorhinostomies (DCR) performed by the traditional external (EX-DCR) approach or an endoscopic (EN-DCR) endonasal approach. A total of 292 consecutive cases with primary nasolacrimal obstruction underwent DCR surgery. Orbital computed tomography scan was used to measure lacrimal sac fossa and other related structures and Lac-Q questionnaire was used to compare surgery result. Maxillary portion of lacrimal sac fossa is thicker in failed surgery group than successful surgery group (<0.05). Lateral nasal structures (uncinate process, operculum of the middle turbinate, agger nasi) are dominantly adjusting to lacrimal sac fossa in failed surgery group (<0.05). Patients who underwent EX-DCR has a 6.0-point and EN-DCR group 11.0-point improvement (<0.016) in Lac-Q questionnaire. Patients who have a thick frontal process of the maxilla and uncinate process, operculum of the middle turbinate, ethmoid cells adjusting to lacrimal fossa are prone to have recurrence of nasolacrimal duct obstruction after DCR surgery. The EN-DCR and the EX-DCR approach have an equivalent surgical success rate but improvement in quality of life by using the Lac-Q questionnaire is greater in the endoscopic group when compared with the external.