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Residual thymic tissue is a common incidental finding in thoracic CT of human adults. To determine whether presumed residual thymic tissue is also a common incidental finding in adult dogs, a two part-study was performed. The first part was a prospective, descriptive design where CT examination was performed in six canine cadavers within 24 h after death and presumed residual thymic tissue was examined pathologically. The second part of the study was a retrospective, analytical design where medical records of our institution were searched for thoracic CT scans of adult dogs performed in the year 2020. Age, sex, breed, presence of presumed thymic tissue, location, shape, attenuation, homogeneity, and width of the tissue were recorded and comparisons were performed using these data. In 4 of 6 of the prospective cases, thymic tissue was present on histology and in 2 of 6 dogs the presence of thymic tissue could not be confirmed. For the retrospective study, in 161/169 (95.3%) cases with presumed residual thymic tissue were detected. Shape and size were highly variable with either homogeneous (46.6%), heterogeneous (42.9%), or mixed (10.6%) attenuation. Dogs with presumed residual thymic tissue were significantly younger (median: 9.1 years; range: 1.2-14.3 vs. median: 10.5 years; range: 9.4-12.3) as were dogs with homogeneous attenuation of the tissue (median: 8.1 years; range: 1.2-14.3 vs. median: 9.5 years; range: 4.0-14.3). In conclusion, results indicated that presumed residual thymic tissue is a common CT finding in adult dogs and can be considered incidental.

Evaluation of the sternum is part of the routine examination of small animal thoracic radiographs. However, descriptions on frequency and type of abnormalities are lacking. This retrospective observational study aimed to describe abnormal radiographic findings of the sternum in a cross-section of client-owned dogs and cats undergoing thoracic radiography between 1 January 2019 and 1 January 2021 for reasons unrelated to diseases of the sternum. The study population consisted of 777 dogs (mean age, 7.3 ± 3.9 years) and 183 cats (mean age, 7.3 ± 5.1 years). Sternal abnormalities were observed in 189/777 (24%) dogs and 53/183 (29%) cats, mostly around the intersternebral cartilages, accounting for 32/80 (40%) dogs and 20/35 (57%) cats. This was followed by an abnormal number of sternal segments (8% dogs, range 3-9 sternebrae; 15% cats, range 7-9 sternebra). Pectus excavatum was observed in 6/777 (0.8%) dogs and 6/183 (3%) cats, and pectus carinatum in 18/777 (2%) dogs and 2/183 (1%) cats. Post-traumatic changes, such as subluxation, were observed in nine dogs (1.1%) and three cats (1.6%). Presumed prostatic carcinoma metastasis and malignant lymphoma were observed in two dogs (0.2%). Incidental radiographic sternal abnormalities are common in cats and dogs but mostly of unknown clinical relevance.