Correlated Imaging of the Equine Hyoid Apparatus Using CT, Micro-CT, and Histology.
Authors: Hartl Bettina, Egerbacher Monika, Kneissl Sibylle Maria
Journal: Frontiers in veterinary science
Summary
# Editorial Summary: Equine Hyoid Apparatus Anatomy Understanding the normal anatomical development and junction types of the equine hyoid apparatus has been lacking until now, creating diagnostic uncertainty when interpreting imaging findings in cases of temporohyoid osteoarthritis and related upper airway conditions. Hartl and colleagues analysed CT scans from 200 clinical cases combined with detailed micro-CT and histological examination of cadaver material to map the hyoid apparatus structure and characterise the different articulations connecting its components. Mineralisation of the tympanohyoid cartilage begins as early as 2 years of age; the basihyoid remains incompletely ossified until beyond 2.5 years; and the lingual process typically develops as a separate ossification centre that persists as distinct anatomy in most horses aged 1.5–3 years. The authors identified critical compositional differences between regions—the tympanohyoid joint functions as a true synchondrosis (cartilaginous union), whilst the basihyoid-thyrohyoid and stylohyoid-epihyoid junctions are synostoses (bony fusions) in approximately two-thirds of horses, with the remainder showing synovial joint formation. For practitioners, these findings provide clarity on age-related anatomical variation and fusion patterns, improving interpretation of imaging in young and immature horses, and offering baseline understanding of normal structure against which degenerative or traumatic changes can be evaluated.
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Practical Takeaways
- •Understanding normal hyoid ossification patterns and age-related changes is essential for interpreting head CT scans and diagnosing temporohyoid joint disease
- •The high prevalence of unfused epihyoid-stylohyoid joints (33%) may represent a significant anatomical variation relevant to temporohyoid pathology in younger horses
- •Knowledge of progressive mineralization and ossification timelines helps differentiate normal developmental changes from pathological changes on imaging
Key Findings
- •CT-visible mineralization of tympanohyoid cartilage begins as early as 2 years of age
- •The epihyoid remains unfused with stylohyoid in one-third of horses examined
- •Temporohyoid joint is a synchondrosis; basihyoid-thyrohyoid and stylohyoid-epihyoid junctions are synostoses in two-thirds of horses
- •All horses under 1.5 years had incompletely developed lingual process with separate ossification center