Relationship between clinical parameters and malformations in dogs diagnosed with atlanto-axial instability.

Atlanto-axial instability is a common disease that affects toy-breed dogs. Most cases of atlanto-axial instability are congenital. Furthermore, patients with atlanto-axial instability are predisposed to other concurrent diseases. Therefore, this study aimed to retrospectively determine the presence of concurrent diseases in cases with atlanto-axial instability using imaging data and analyze the relationship between clinical parameters and the incidence of complex malformations. The clinical data and imaging findings of 41 toy-breed dogs diagnosed with atlanto-axial instability were analyzed using their medical records and imaging data. Occipital dysplasia (17/27), atlanto-occipital overlapping (22/34), dens dysplasia (27/41), Chiari-like malformation (8/34), syringomyelia (5/34), lateral ventricular enlargement (20/36), and intracranial arachnoid cyst (5/35) were observed in patients with atlanto-axial instability. The body weight of the patients in the groups with atlanto-occipital overlapping and lateral ventricular enlargement was lower than that of those in the groups without these diseases (1.78 ± 0.71 vs 2.71 ± 1.15 kg, P = 0.0269, 1.60 ± 0.40 vs 2.75 ± 1.08 kg, P = 0.001, respectively). Furthermore, when the correlation between the total number of concurrent diseases and the age at onset and body weight was examined, it became clear that lower body weight was associated with the incidence of a greater number of concurrent diseases. Thus, the findings of this study suggest that toy-breed dogs are more likely to present with complex malformations and should be evaluated carefully with additional examinations and treatment methods.

Osteosarcoma of the hyoid bone in a cat.

Case summary: A 10-year-old male neutered Abyssinian cat was presented with the chief complaint of a right pharyngeal mass. On palpation, the mass was easily palpable; it appeared well demarcated and mobile, and oval in shape. Radiographic examination showed a radiopaque pharyngeal mass, which was revealed to be a well-demarcated mass lesion with a radiopaque marginal area on CT examination. The inside of the mass was uniformly well enhanced on contrast CT examination. A three-dimensional image reconstructed from the CT images strongly suggested that the mass originated from the right stylohyoid bone. No abnormal lesions were observed in the thoracic and abdominal CT examinations. Surgical excision of the mass was scheduled 3 weeks after the first admission. The mass was bluntly separated from the surrounding musculature and resected together with the ipsilateral epihyoid bone adjacent to the mass. Histopathological examination of the resected mass showed neoplastic cells with osteoid formation, and the mass was histopathologically diagnosed as an osteosarcoma. The postoperative recovery from anaesthesia was uneventful, and the cat began feeding on its own from the third postoperative day. The 3-month postoperative CT evaluation revealed no local recurrence or distant metastasis. The cat showed no abnormal findings at the time of writing (6 months postoperatively). Relevance and novel information: Although osteosarcoma derived from the hyoid bone has rarely been reported in the veterinary field, this report suggests that such tumours may occur in cats. In addition, partial excision of the hyoid apparatus seems to be well tolerated in cats.