Correlated Imaging of a Presumed Normal Equine Hyoid Apparatus using CT, MICRO-CT and Histology.

Introduction Several publications address computertomographic changes of the hyoid, mainly of the temporohyoid joint. However, studys describing the normal CT- anatomy of the entire hyoid apparatus are rare. Therefore, we want to describe the normal CT-anatomy of the complete hyoid apparatus using computertomography, micro-CT and histology. Materials and Methods We retrospectively reviewed the clinical records of the Veterinary University Vienna between 2009 and 2018. We selected horses that underwent a head CT-scan. Inclusion criteria for the CT-scans were visibility of at least two of the four joints of the hyoid apparatus. Additionally, we processed 10 cadaver heads using CT, micro-CT of selected joints and histology of all joints. Results 200 CT-scans matched the inclusion criteria. Mineralisations within the tympanohyoid cartilage occurred in 38% of horses. A separate epihyoid between stylohyoid and ceratohyoid was present in 33% of horses. The lingual process was not-fully developed in horses under 1,5 years. Between 1,5 and 3 years, 10/11 horses had a separate ossification center of the lingual process. Conclusion In summary, findings from the current study indicated that the hyoid apparatus imaging anatomy shows normal variations in reviewed horses. The clinical significance of these findings is presently unknown, therefore, future studies should address changes of the hyoid and their association to clinical symptoms and/or preceded manipulations.

• VetImaging