Structure of the lateral mass of the ethmoid by curved stacking of endoturbinal elements

Context According to evo-devo theory, the embryonic development of the nasal organ mimics its phylontogenic formation: the lateral masses of the human ethmoid bone develop by curved “onion” stacking of the endoturbinals (the horizontal bone septa of the mammalian olfactory chamber) under the impact of facial and skull-base remodeling, rather than by pneumatization of cavities communicating via ostia. Objectives To assess the frequency of the onion structure on coronal CT. Material and methods Three independent examiners performed a retrospective descriptive study of coronal CT scans taken ahead of septorhinoplasty between June 2010 and December 2012 in adult patients without history of sinonasal surgery. Results Fifty patients were included. In the anterior right and left and posterior right ethmoid, an onion arrangement of the endoturbinals was systematically found on at least 1 view, and on 60% of views taking all ethmoid compartments together. Two endoturbinals were generally involved, but a rolling-up of 3 endoturbinals was also observed, significantly more frequently in the posterior compartments (P = 0.004 on the right side, P = 0.012 on the left). Conclusion The onion structure of the lateral masses of the ethmoid can be observed on coronal CT scans. This structure confirms evo-devo theory. The ethmoid thus appears fundamentally different from the paranasal sinuses, suggesting that the pathogenesis of nasal polyposis and ethmoidectomy techniques need to be reconsidered.