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

Radiographic imaging can now reliably localize the equine middle conchal sinus (MCS), improving diagnosis of sinusitis in this often overlooked sinus compartment when advanced CT imaging is unavailable.

Research Background

• The middle conchal sinus (MCS), also known as the ethmoidal sinus, is one of the less understood paranasal sinuses in horses.
• Despite its role in sinonasal diseases, disorders of the MCS are frequently underdiagnosed due to limited anatomical knowledge and difficulty visualizing it on standard radiographs.
• Computed tomography (CT) provides better imaging but is not always accessible in clinical settings.

Objectives

• To characterize the radiographic features and anatomical location of the equine MCS using standard radiographic projections combined with anatomical dissection.
• To demonstrate the clinical relevance of these findings by correlating them with two clinical cases of MCS sinusitis confirmed by CT.

Methodology

• Six equine cadaver heads representing a range of ages were studied.
• Each head underwent standard radiographic imaging before and after sagittal sectioning.
• Wire markers were placed to outline the boundaries of the MCS after dissection, facilitating correlation between radiographs and actual sinus anatomy.
• Radiographs were reviewed to identify anatomical landmarks and the visibility of the MCS.
• Two clinical cases with confirmed MCS sinusitis by CT were reviewed to compare with cadaveric observations and radiographic findings.

Key Findings

• Pre-dissection radiographs generally did not clearly show the MCS, confirming difficulty in visualizing this sinus with standard views.
• Post-sagittal sectioning radiographs with wire markers highlighted consistent landmarks for identifying the MCS:
• The MCS appeared as an ovoid (egg-shaped) structure superimposed over the ethmoturbinates.
• It was located dorsally (above) the third maxillary molar teeth (Triadan 11).
• Latero-lateral (side-to-side) radiographic views were most useful for identifying this sinus and its shape.
• Oblique projections helped determine which side of the head was affected.
• Dorsoventral (top-to-bottom) views consistently showed the MCS superimposed on the middle nasal meatus, nasal septum, and rostral margin of the ethmoturbinates, allowing approximate localization in all specimens.
• Clinical cases demonstrated pathologic changes correlating with these radiographic landmarks and anatomical locations observed in the cadaveric heads.

Implications for Clinical Practice

• The study establishes reproducible radiographic references to locate the MCS using standard radiographic views, even without CT imaging.
• Increased awareness of MCS anatomy and its radiographic appearance may lead to improved diagnosis of sinus diseases involving this compartment, which is otherwise challenging to detect.
• This can be particularly valuable in clinical contexts where CT imaging is unavailable or not feasible.

Study Limitations

• The sample size was relatively small, with six cadaver heads, which may limit generalizability.
• Radiographic evaluation was performed by a non-blinded reviewer, raising potential for observer bias.

Conclusions

• This research provides a useful anatomical and radiographic framework for identifying and diagnosing middle conchal sinus conditions in horses.
• The findings bridge a key gap in equine sinus imaging by enabling better recognition of the MCS on conventional radiographs.
• Ultimately, this will support veterinarians in earlier and more accurate identification of MCS-related sinusitis, improving clinical outcomes.