Endoscopic anatomy of the lacrimal sac for dacryocystorhinostomy

OBJECTIVES To assist the endoscopic localization of the lacrimal sac (LS)  relative to nearby landmarks. Methods: This is a descriptive prospective anatomical study. Sixteen lateral nasal walls were dissected endoscopically to identify and localize the LS between October and November 2015. Multiple measurements were obtained from the NS to the anterior and posterior walls of the LS, as well as to the middle turbinate axilla (MTA) and from the MTA to the LS borders. Results: The average distance from the NS to the anterior border of the LS was 42.0 mm and the posterior border was 48.5 mm. The average widths of the LS were 7.55 mm superiorly, and 6.6 mm inferiorly representing a mathematical proof that the LS is a trapezoid shape. The mean distance from the NS to the MTA was 47.3 mm. Nine of the 16 lacrimal sacs (56.3%) were found to be partially overlapped by the MTA. The LS was only totally overlapped and lying posterior to the MTA in one side (6.3%), while in 6 sides (37.5%) the LS lay anterior to the MTA. Conclusion:  Endoscopic surgeons should be aware of the location of the LS relative to nearby landmarks, particularly the MTA. Representing a mathematical proof that the LS is wider at it upper part than lower part best presented as a trapezoid shape. We have provided additional measurements that may prove useful in cases of difficult exposure.