Abstract
During a routine abdominal ultrasound, a 28 yr old female California sea lion (Zalophus californianus) presented with a mass within the right liver lobe. The heterogenous and hyperechoic mass was well demarcated and approximately 5cm by 8 cm in size. Small hyperechoic foci, 1 mm diameter were also noted in the spleen. There was no ascites. The animal was asymptomatic, with normal weight, appetite and behavior. Hematological and biochemistry parameters were all within normal range, except for gamma glutamyltransferase, which was elevated (226 U/L, range 20-123 U/L).2 Review of previous routine blood samples showed a gradual elevation of gamma glutamyltransferase (GGT) on 3 previous samples, obtained at 6 months intervals. In marine mammals increased serum GGT can be associated with cholestasis. Differential diagnoses included bacterial abscess, fungal infection and neoplasia. Thoracic radiographs were obtained under training and did not reveal any abnormalities. To further define the mass, general anesthesia was scheduled to perform a computed tomography (CT) scan and a biopsy. Vitamin K1 (1.25 mg/kg) BID was administered per os. (PO). The following day, the animal was premedicated with diazepam (0.3 mg/kg) PO for transportation, then midazolam (0.25 mg/ kg) and butorphanol (0.25 mg/kg) were administered by intramuscular (IM) injection. The sea lion was intubated and maintained with isoflurane in oxygen (2.5-5%). The CT showed that multiple masses were present in the right liver lobe, ranging from 1 to 6 cm, as well as in other hepatic lobes, ranging between 1 and 2 cm diameter. A few foci were also suspected in the spleen. All other visceral structures were normal. Three biopsy samples were obtained from the main liver mass, under ultrasound guidance, using a 14G x 2cm automatic tru-cut system (Temno Evolution®). The animal recovered uneventfully and was released in water the following day.
The samples were fixed in neutral buffered formaldehyde (10%), paraffin blocked and hematoxylin-eosin stained slides obtained. The liver tissue showed disruption of acinar architecture, irregular crowded lobules with inflammatory infiltration. Trabeculae of round to polygonal cells with poorly defined cell boundaries were present. There were prominent nucleoli and increased number of bizarre mitotic figures. This was consistent with hepatocellular carcinoma (HCC).
Hepatocellular carcinoma is a highly malignant tumour in humans and various species of mammals, which metastasizes to the lymph nodes, lungs or the spleen. Some hepatocellular carcinomas extensively spread within the liver (intrahepatic metastasis). It is an uncommon tumor in domestic species. Post mortem diagnosis of HCC with metastases to the spleen has been described in a free ranging California sea lion.1 Known risk factors for HCC in humans include chronic viral hepatitis infection, excessive hepatic iron levels, and aflatoxin contamination of the diet. Environmental contaminants have been proposed as possible contributing factors to carcinogenesis in marine mammals.4 Exposure may occur in utero, through lactational transfer and via contaminated food sources. These risk factors have to be evaluated for this species. In captive female otariids, iron accumulation may lead to hemochromatosis.3 In this case report, the pathogenesis of neoplasia formation has not been established.
Nine months after the initial detection of the tumor by ultrasound, the animal's appetite and behavior are good. Regular ultrasound examinations to monitor the size and appearance of the hepatic and splenic lesions, as well as any development of ascites are performed. To our knowledge, this is the first reported case of antemortem diagnosis of hepatocellular carcinoma in a California sea lion.
References
1. Acevedo-Whitehouse K, et al. 1999. Hepatic carcinoma with spleen metastasis in a California sea lion from the Gulf of California. Journal of Wildlife diseases 35(3):565-568.
2. Bossart GD, et al., 2001. Clinical pathology. In: CRC Handbook of Marine Mammal Medicine, Dierauf L and Gulland FMD. CRC Press, Pp. 383-448.
3. Garcia AR, et al., 2000. Hemochromatosis in captive otarids. Proceedings of the International Association for Aquatic Animal Medicine; p. 197.
4. Newman SJ, Smith SA. 2006. Marine mammal neoplasia: a review. Veterinary Pathology 43(6):865-880.