The creation of a 3D model of modal anatomy of the ethmoid could, like other parts of the body, improve anatomical, radiological and perhaps even surgical learning. Anatomical variations might constitute a "background noise" of the modal anatomy, which can be attenuated by multiplying the instances of acquisitions. The objective of this work is to establish modal anatomy of the ethmoid by the analysis of a large number of CT-scan acquisitions carried out in individuals with no acquired sinus pathology.

Non-interventional descriptive research.

Sinus CTscans (period 2016-2019) will be reviewed from the PACS database of the CHRU of Nancy and selected in individuals without sinus pathology. All CT-scans will be fully anonymized. 26 landmarks will be pointed out to enable :

1. prior images alignment (centering on the median line, realignment rotations then resizing)
2. a mean and median calculation, allowing to establish a mean and median ethmoid model
3. calculation of standard deviations for each voxel The structures obtained in this way (bone, tissue or aerial) will be described anatomically.

Retrospective analysis of sinus CT scans images from individuals (period 2016-2019)

Inclusion Criteria:

All individuals (>18 years all) with a sinus CT scan available in the CHRU database

Exclusion Criteria:

inflammatory sinus disease (eg. nasal polyposis, aspergilloma, ...) evolutive sinus tumor anatomical abnormality (e.g. post traumatic, prior sinus surgery, embryologic abnormality...)

All patients who had a sinus CT-scan during the 2016-2019 period.