A CT-Based Novel Way to Define Ethmoidal Foramina Topography in Human Orbits: Not So Variable After All

Ethmoidal foramina are the inlets of important channels that connect the orbit with cranial, nasal and paranasal cavities. They host arteries that sometimes feed intracranial vascular anomalies or are the source of refractive epistaxis. Standardization of their exact topography may be relevant for neuronavigation in orbital surgery. A retrospective study was carried out on computed tomographies carried out for pathologies not altering the structural integrity of the medial orbital wall. By opportunely reorienting computed tomography spatial planes, a series of measures were taken to devise the following indexes for anterior and posterior ethmoidal foramina: average and median digital relative depth index (RDI) to standardize anterior and posterior ethmoidal foramina positions on an anteroposterior direction, and average digital relative height index (RHI) for vertical standardization. A digital RDI watershed index (RDIwi) was also devised for the correct assignment of ethmoidal foramina to the anterior and posterior types. The digital RDIwi appeared effective for ethmoidal foramina classification when orbits contained just one or more than 2 ethmoidal foramina. Whereas the average digital RHI did not appear a very effective tool for vertical standardization of ethmoidal foramina, the median and average digital RDIs were predictive of ethmoidal foramina localization in the anteroposterior direction with a tolerance of about 2 mm in 50% of cases. The effectiveness of median and average digital RDIs to locate anterior and posterior ethmoidal foramina along the orbital wall make these indexes good candidate parameters for neuronavigation in orbital surgery.