Radiographic identification and description of the equine middle conchal sinus ( ethmoidal sinus ): Implications for diagnosing middle conchal sinusitis

Background The middle conchal sinus (MCS) (ethmoidal sinus) remains one of the least understood equine paranasal compartments. Despite recognition of its involvement in sinonasal disease, disorders of the MCS often remain underdiagnosed in the absence of computed tomographic (CT) imaging due to limited anatomical understanding and challenges with radiographic visualisation. Objectives The objectives of the study were (1) to characterise the radiographic features and anatomical location of the MCS in horses and (2) to illustrate the practical relevance of the anatomical and radiographic findings in two clinical cases of MCS sinusitis. Study Design Descriptive anatomical and imaging study. Methods Six equine cadaver heads representing different age groups underwent standard radiographic projections before and after sagittal sectioning and placement of wire markers outlining the MCS. Radiographs were evaluated to identify and describe anatomical landmarks. Two clinical cases of MCS sinusitis confirmed by CT were used for comparative assessment. Results The MCS was not readily identifiable on pre‐dissection radiographs. Post‐sectioning images revealed consistent latero‐lateral radiographic landmarks, notably its ovoid shape superimposed on the ethmoturbinates and its location dorsal to the third maxillary molar (maxillary Triadan 11's). Oblique projections allowed differentiation on which side was affected. On dorsoventral projections, the MCS was consistently superimposed on the middle nasal meatus, the nasal septum and the rostral margin of the ethmoturbinates, allowing tentative localisation in all specimens. The clinical cases had pathological changes at the predicted MCS site, correlating with cadaveric observations. Main Limitations The main limitations of the study include the small number of specimens examined and that radiographic interpretation was performed by a non‐blinded reviewer. Conclusions This study provides a reproducible radiographic reference for localising the MCS using radiography. Improved awareness of its location and presentation on radiographs will aid clinicians in diagnosing sinus disease involving this compartment, especially when CT imaging is unavailable.