Reference role of middle turbinate axilla in lacrimal sac localization assisted by computed tomographic dacryocystography-reference value of middle turbinate in locating lacrimal sac

BACKGROUND: The middle turbinate axilla (MTA) has always been used as a stable anatomic landmark for endoscopic surgeons to locate the lacrimal sac on the lateral nasal wall. Yet, little is known about whether the lacrimal sac size will affect the positioning effect of MTA on lacrimal sac. The aim of this study was to investigate the regularity of lacrimal sac size and lacrimal sac localization through the reference position of the MTA on computed tomographic dacryocystography (CT-DCG) images. METHODS: A series of 192 endoscopic dacryocystorhinostomy (DCR) surgeries were performed. All the patients had been diagnosed as unilateral nasolacrimal duct obstruction and received CT-DCG examinations. According to the maximum transverse diameter of the lacrimal sac on CT-DCG, the patients were classified into three groups. Measurements were taken on CT-DCG parasagittal images. RESULTS: The average distance from the sac superior fundus (SSF) to the MTA was 7.52 mm ± 3.23 mm, and it increased with the increase of the maximum transverse diameter of the sac among groups (p < 0.01). The average distance from the common canaliculus (CC) to the MTA was 3.95 mm ± 2.49 mm. No significant difference was observed among the groups (p = 0.11). The average distance from the CC to the SSF was 3.41 mm ± 1.31 mm, and it increased with the increase of the sac transverse diameter among groups (p < 0.01). CONCLUSIONS: The lacrimal sac can be accurately located on the lateral nasal wall by the reference position of the MTA on CT-DCG images. The distance of the SSF to the MTA and the SSF to the CC is related to the lacrimal sac size. The relative position of the CC to the MTA is relatively stable on CT-DCG images, which make it possible to locate the lacrimal sac of different sizes and the corresponding nasal mucosa incision design in endoscopic DCR.