Comprehensive radiological assessment of ethmoid skull-base anatomy: beyond the Keros classification

The Keros classification has been the traditional standard for stratifying olfactory fossa depth and predicting skull-base risk during endoscopic sinus surgery (ESS). However, accumulating evidence from multicenter CT studies across different populations demonstrates that Keros type alone does not correlate with other clinically important skull-base parameters, including ethmoid roof asymmetry, orbit-referenced skull-base height indices, and the position of the anterior ethmoidal artery (AEA) in relation to supraorbital ethmoid cells (SOECs). This narrative review synthesizes contemporary radiological literature to evaluate the role of additional CT-based measurements in refining preoperative risk assessment for skull-base injury. We review 15 key publications spanning populations from the Middle East, Europe, and South Asia, emphasizing that a multi-parameter approach – including Keros classification, asymmetry assessment, AEA-to-skull-base distance, and SOEC variants – provides a more comprehensive and clinically actionable description of ethmoid skull-base anatomy than traditional Keros classification alone. We also highlight the implications of these anatomical variations for surgical planning in patients with chronic rhinosinusitis, allergic fungal rhinosinusitis, and increased cerebrospinal fluid leak risk. Future prospective studies linking preoperative CT phenotypes to surgical complication rates are needed to validate these expanded parameters.