RESUMEN
INTRODUCTION: Although several studies have tried to identify the causes of failure of dacryocystorhinostomy (DCR) surgery, the ethmoid sinus remains an underestimated and little described source of failure. OBJECTIVE: To study anatomical relationship between the ethmoidal sinus, particularly the "Agger nasi" cell, with the lacrimal fossa in the North African population, little described in the literature. This study is based on the results of preoperative analysis of dacryo-computed tomography. PATIENTS AND METHODS: Analysis of preoperative computed tomography images of patients undergoing dacryocystorhinostomy over a 7-year period from January 2011 to December 2017. Anatomical relationships were studied according to the following classification: type I: No ethmoid cells located anteriorly to the posterior lacrimal crest on transverse images; type II: ethmoidal cells extending anteriorly to the posterior lacrimal crest, but not reaching the anterior edge of the lacrimal bone; Type III: ethmoidal cells located anterior to the lacrimal bone suture. RESULTS: Two hundred and fifteen preoperative computed tomography images were analyzed. The morphology of the ethmoid sinus was classified as type 1 in 33.5%, type 2 in 42.32% and type 3 in 24.18%. Computed tomography analysis was symmetrical in 87.5% and asymmetrical in 12.5%. CONCLUSION: During dacryocystorhinostomy, the surgeon must take into consideration type III, which can be present in 25% of cases. In the case of surgical failure, a dacryo-CT must be performed to rule out such anterior positioning of the ethmoid cells.