CT and MRI Unlock the Salivary Map: First Reference Atlas for Donkey Glands

Major Salivary Gland Examinations of the Donkey (Equus asinus) Using Sectional Anatomy, Computed Tomography and Magnetic Resonance Imaging

Jamal Nourinezhad, Albert Abdi, Abdolvahed Moarabi, Mohamad Ghasem Hanafi, Rahmat Allah Fatahian Dehkordi, Anna Tomańska

Background:
Accurate evaluation of the major salivary glands (MSGs) in donkeys is clinically relevant but historically limited by poor visualization on standard radiographs. Advanced cross-sectional imaging techniques such as computed tomography (CT) and magnetic resonance imaging (MRI) offer improved anatomic detail but have not been previously applied to donkey MSGs. This study aimed to establish detailed anatomical references for the parotid, mandibular, and polystomatic sublingual glands in donkeys using sectional anatomy correlated with CT and MRI.

Methods:
Seven healthy adult donkeys were euthanized and imaged postmortem using 64-slice CT and 1.5 Tesla MRI. After imaging, heads were frozen and transversely sectioned at key anatomical levels. CT and MRI images were matched with corresponding anatomical cross-sections and labeled using standard veterinary anatomical nomenclature. The visibility and anatomical relationships of the salivary glands were assessed across imaging modalities.

Results:
The parotid salivary gland (PSG) was consistently identified ventral to the external auditory canal, the mandibular salivary gland (MSG) was divided into cranial and caudal lobes with distinct anatomical landmarks, and the polystomatic sublingual salivary gland (PSSG) was visualized only in CT, not MRI. CT landmarks included the atlas wing, thyroid cartilage, and mandibular body; MRI landmarks included the external auditory canal, guttural pouch, and maxillary vein. The MRI signal for the PSG and MSG was high on T2-weighted sequences, with the PSG appearing more heterogeneous. Key species differences from the horse included absence of perforation of the PSG by the maxillary vein.

Limitations:
Only transverse sections were analyzed; dorsal and sagittal planes were not evaluated. Imaging was performed postmortem, which may alter tissue contrast. The study did not include contrast-enhanced imaging or ultrasonography, and the sample size was limited to seven animals. Glandular ducts were not consistently visualized, particularly in MRI.

Conclusions:
This study provides the first detailed reference atlas of donkey MSGs using matched anatomical, CT, and MRI sections. The data establish critical imaging landmarks for diagnostic interpretation and may assist in evaluating salivary gland pathology, planning surgery, or guiding ultrasonographic evaluation in this species. These findings also highlight notable anatomical differences between donkeys and horses that are important for clinical practice.

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