June 12, 2024

Normal Thoracic Radiographic Anatomy of Immature California Sea Lions (Zalophus californianus) and Immature Northern Elephant Seals (Mirounga angustirostris)


Sophie E. Dennison, Lisa Forrest, and Frances M. D. Gulland


Abstract: Immature California sea lions (Zalophus californianus) and northern elephant seals (Mirounga angustirostris) without evidence of thoracic disease were radiographed under anesthesia. Important species-specific variations were noted on thoracic radiographs. For the California sea lions, the mean vertebral heart score was 8.65 from the left lateral view, and the cardiac silhouette occupied a mean of 66% of the internal thoracic width. The tracheal bifurcation in California sea lions was located at the level of the first thoracic vertebral body. For the northern elephant seals, there was variation in the number of thoracic vertebrae and ribs from 12 to 15, a lack of pulmonary lobation, and an indistinct cardiac silhouette. Cardiac measurements could only be made on ventrodorsal (VD) and dorsoventral (DV) digital radiographs where the cardiac silhouette occupied a mean of 62% of the internal thoracic width. The combination of smooth to rounded lung lobe margins with border effacement of the cardiac silhouette and diaphragmatic margin is an important, normal, species-specific finding of the northern elephant seal that could be easily mistaken for pleural effusion. The carina in the northern elephant seals was at the level of the fifth thoracic vertebral body. In both species, the aortic bulb was evident as a focal, fairly symmetrical cranial mediastinal widening cranial to the cardiac silhouette on the VD and DV views, resulting in the aorta being identifiable on both the right and the left. This is an important normal finding in marine mammals that should not be mistaken for pathology. Both species had a diffuse bronchointerstitial pulmonary pattern that was slightly more prominent in California sea lions. This finding was consistent with variation between these species in the tissues supporting the small airways.

This prospective study serves as a normal reference for immature California sea lions and northern elephant seals in veterinary care.

Key Words: Radiology, radiography, diagnostic imaging, marine mammal, seal, vertebral heart score, lung, trachea, pinniped, California sea lion, Zalophus californianus, northern elephant seal, Mirounga angustirostris

Document Type: Research article

DOI: 10.1578/AM.35.1.2009.36

Page Numbers: 36-42

Info SKU: Vol__35__Iss__1__Dennison_et__al_ Category: