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- CT for THO
Rupert F Dash 1, Justin D Perkins 1, Yu-Mei Chang 1, Rhiannon E Morgan 2
Background
Temporohyoid osteoarthropathy (THO) is a degenerative or possibly infectious condition of the equine temporohyoid joint (THJ), characterized by bone proliferation and cartilage ossification. The disease may cause serious neurological signs but its pathogenesis remains unclear. This study aimed to describe the range of computed tomography (CT) changes in the THJ of horses presented for unrelated reasons, and to investigate associations between imaging findings and potential risk factors including age, breed, clinical signs, and CT diagnoses.
Methods
A cross-sectional retrospective study was conducted on 424 horses undergoing CT scans of the head and cervical spine between 2017 and 2021. Each temporohyoid joint was graded for bone proliferation and tympanohyoid cartilage changes on a 0–3 scale, with a sum grade calculated by combining both scores. Multivariate ordinal logistic regression was used to assess associations between imaging grades and risk factors such as age, sex, breed, presenting complaint, and CT findings. Follow-up owner questionnaires were used to collect clinical outcomes.
Results
Moderate osseous proliferation (bone grade 2) was the most common finding, while cartilage ossification (grade 0) was uncommon. Osseous changes were most frequently bilateral, originating from the temporal bone, and most often located medially and caudally. Increased THJ grade was significantly associated with age, Thoroughbred and Arabian breeds, and imaging findings such as temporal bone fragmentation and soft tissue swelling. However, there was no significant association between THJ grade and clinical signs at presentation. A CT diagnosis of THO was associated with increased cartilage and sum grades but not with bone grade alone. Lateral bone proliferation, although infrequent, correlated with higher sum grades.
Limitations
A single trained observer evaluated all images, introducing potential bias. Genetic predisposition was not assessed, and histological confirmation of CT findings was not obtained. Breed-related findings may be affected by population composition, and inclusion of observer training cases in the final dataset might have influenced results. Follow-up data relied on owner reporting, which may be imprecise.
Conclusions
Moderate temporohyoid joint remodeling is common in horses undergoing CT for unrelated issues and may not be clinically significant. However, cartilage ossification, lateral bone proliferation, and associated findings like soft tissue swelling and temporal bone fragmentation may be more indicative of disease. Thoroughbreds and Arabians appear predisposed to greater THJ changes. The findings support a primarily degenerative etiology for THO, rather than an infectious one.
Transverse computed tomographic images at the level of the temporohyoid joint demonstrating the bone grades. (A) Grade 0: no bone proliferation, (B) grade 1: proliferation not bridging the joint (white arrow), (C) grade 2: proliferation bridging the joint (white arrow), (D) grade 3: proliferation extending over 1 cm (digital calliper). Helical acquisition, 120 kV and 400 mA, 512 × 512 matrix, 0.625 mm slice thickness 0.3 mm slice interval, WW: 2800, WL: 800, bone kernel reconstruction.
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