Sternal Abnormalities on Thoracic Radiographs of Dogs and Cats

Abstract

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.

Keywords: companion animals; dislocation; malformation; osteoarthrosis; pectus carinatum; pectus excavatum; vacuum phenomenon.

Figure 1

(Left) panel: Example of a left lateral radiograph of a dog with a sternum that was considered normal. (Right) panel: Abnormally short sternum in a 9-year-old, female neutered Bearded Collie. Caudad to the manubrium of the sternum, fusion of two to three shortened sternebrae with complete absence of the caudal part of the sternum is noted. The diaphragm shows cranial excursion, and the cardiac silhouette is mildly dorsally displaced. Vacuum phenomenon is visible between the manubrium of the sternum and second sternebra.

Figure 2

(Top left) panel: Degeneration of the intersternebral joint space in an 11-year-old, neutered female Welsh Springer Spaniel. The intersternebral cartilage space between the 4th and 5th sternebrae is narrowed, shows vacuum phenomenon, and is surrounded by new bone formation. The 5th sternebra is mildly displaced ventrally relative to the fourth sternebra. (Bottom left): Pectus excavatum in a 12-year-old male Pug. Dorsal deviation was noted in the caudal part of the sternum with border effacement of the ventral thoracic diaphragmatic surface and the caudal ventral cardiac silhouette and an altered position of the heart. (Top right): Luxation of the second sternebra in a 10-year-old male neutered mixed-breed dog. The second sternebra is displaced in craniodorsal direction and is overriding the manubrium of the sternum. (Bottom right): Pathologic fractures of multiple sternebrae in 10-year-old male Chihuahua with malignant lymphoma.

Figure 3

(Top left) panel: Example of a left lateral radiograph of a cat with a sternum that was considered normal. (Bottom left): Abnormal low number of sternebrae in a 12-year-old female Domestic Shorthair. A total of six individual sternebrae are present, caused by fusion of the fifth and sixth sternebrae and an absence of the seventh sternebra. (Top right): Pectus excavatum in an 11-year-old female neutered Domestic Shorthair. (Bottom right): Chronic subluxation of the fourth sternebra in an 11-year-old male neutered Domestic Shorthair. The fourth sternebra is displaced dorsally and fused with the third sternebra.