Radiographic identification and description of the equine middle conchal sinus (mcs): implications for diagnosing mcs sinusitis.

The middle conchal sinus (MCS), also termed the ethmoidal sinus, remains one of the least understood equine paranasal compartments. Despite recognition of its involvement in sinonasal disease, it remains underdiagnosed in absence of CT due to limited anatomical understanding and challenges with radiographic visualization.
Materials and Methods
Three 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 consistent anatomical landmarks. A clinical case of MCS sinusitis confirmed by CT was used for comparative assessment.
Results
The MCS was not identifiable on pre-dissection radiographs. Post-sectioning images revealed consistent latero-lateral radiographic landmarks, notably its ovoid shape superimposed with the ethmoid turbinates and located dorsal to the third maxillary molar (111/211). Oblique projections allowed side differentiation. On dorsoventral projections, the MCS was consistently superimposed with the middle nasal meatus and the rostral margin of the ethmoid turbinates, allowing tentative localization in all specimens. The clinical case demonstrated pathology at the predicted MCS site, correlating with cadaveric observations.
Relevance to Clinical Practice
This study provides a reproducible radiographic reference for localising the MCS using widely available imaging techniques. Improved awareness of its location and presentation on radiographs will aid clinicians in diagnosing sinus disease involving this compartment, especially when CT is unavailable. This work also highlights the need to reassess the role of the MCS in persistent or atypical sinusitis.