Abstract

Stranded California sea lions (Zalophus californianus; CSL) frequently present with renal disease, and prognosis for affected animals is often guarded to poor. Rapid diagnosis of the cause of the renal disease is critical for triage and initiation of appropriate treatment. Serum chemistry is a valuable diagnostic tool; however, results do not specify cause. Ultrasound images were reviewed and compared with gross necropsy examination from 49 CSL admitted to The Marine Mammal Center (Sausalito, CA) between 2017 and 2020. Animals that died or were euthanized without evidence of renal disease by ultrasound or grossly were normal controls (n=8). Animals with leptospirosis showed characteristic, strikingly increased echogenicity of the cortices with comparatively hypoechoic medulla; findings matched the pale expanded cortices with corticomedullary congestion/hemorrhage observed grossly (n=27). Similar ultrasonographic appearance was documented in 46 CSL with azotemia that survived to release; azotemia was noted on serum chemistry, and leptospirosis was confirmed with serology. Uni- or bilateral hydronephrosis and hydroureter were confirmed in CSL with urogenital carcinoma (n=12). One CSL with bacterial pyelonephritis had multifocal hyperechoic punctate to nodular foci throughout the parenchyma, which correlated grossly with focal liquefactive necrosis and suppurative exudate. Nodules of mixed echogenicity were noted in a sea lion with disseminated sarcocystosis. Renal ultrasound is a particularly valuable non-invasive diagnostic tool for accurate assessment of common causes of renal disease and is highly recommended to facilitate rapid treatment and triage of stranded CSL.

Acknowledgements

The authors thank Sarah Pattison, Lauren Campbell, Sophie Guarasci, Kelly Miller, Liz Eby, Amy Rubenstein, Dane Whitaker, and Shawn Johnson as well as the staff, volunteers, and donors of The Marine Mammal Center for their excellent animal care and support.