RESUMO
OBJECTIVE: Describe a reliable anatomical landmark that can be used to locate the maxillary sinus natural ostium (MSNO) during endoscopic surgery, even if the uncinate process is preserved. DESIGN: Descriptive anatomical. SETTING: An anatomical and radiological study was performed to evaluate the consistency of the landmark, denominated "M" line. SUBJECTS AND METHODS: Dissections were performed in 57 cadaver heads (114 sides). In addition, 73 computerised tomography (CT) scans (146 sides) of patients with chronic inflammatory sinonasal disease were analysed using a three-dimensional (3D) reconstruction computer program. RESULTS: The "M" line crossed the MSNO in 112 dissected sides (98.2%) and 140 sides at CT 3D reconstruction (95.9%). CONCLUSION: The "M" line is a reliable anatomical landmark for predicting MSNO location. As such, it could improve and facilitate endoscopic sinus surgery, using traditional, minimally invasive or uncinate preserving techniques.