Hepatocellular carcinoma and suspected splenic hemangiosarcoma in a potbellied pig

Abstract

A 10-year-old, lethargic, potbellied pig presented with signs of abdominal discomfort and a palpable abdominal mass. Laparotomy revealed a 20 cm diameter mass on the spleen and smaller masses on the omentum and liver. After euthanasia and histologic examination of the hepatic mass, the diagnosis was hepatocellular carcinoma.

A 10-year-old, castrated, male potbellied pig with a 1-day history of lethargy was examined during a house call (day 1). The pig was an in- and outdoor pet weighing approximately 80 kg, with no history of medical problems. Body temperature, taken by the owner, was within normal limits. The pig displayed signs of abdominal discomfort, including a hunched posture and reluctance to move. When abdominal palpation was attempted, the pig squealed and tensed his abdominal musculature.

The primary concern was urethral obstruction due to crystalluria or uroliths. Differential diagnoses included dietary indiscretion with secondary gastroenteritis or obstruction; an intestinal accident, such as intestinal torsion or intussusception; metabolic disease; and neoplasia. There was no history of access to toxicants. The owner was instructed to monitor the pig for urination, and to provide supportive care by encouraging eating and drinking.

On day 3, the pig was admitted to the hospital for reexamination. The owner had not observed urination during this time, and lethargy and anorexia had increased. Urethral obstruction was strongly suspected. Abdominal palpation was again unsuccessful. The pig was anesthetized to palpate the abdomen and perform radiography and surgery, if necessary.

General anesthesia was induced and maintained with isofluorane (Aerrane; Ohmeda PPD, New Jersey, USA) through a mask on a partial rebreathing circle system. When the pig was positioned on the examination table, a small amount of urine was voided. The bladder was palpated in the caudal part of the abdomen and was fluctuant and of normal size. As urine was easily expressed through the urethra with gentle pressure on the bladder, urethral obstruction was ruled out.

A firm, round mass, approximately 20 cm in diameter, was palpated in the right middle part of the abdomen and was somewhat mobile. Neoplasia was the primary differential diagnosis, as the mass was too large to be a gastrointestinal foreign body. An exploratory laparotomy was performed to confirm the diagnosis and assess organ involvement.

The pig was placed in dorsal recumbency and a ventral midline incision was made, starting 10 cm caudal to the xiphoid process and extending caudad for 20 cm. Blood clots were noted in the peritoneal cavity. A dark red mass, 20 cm in diameter and with an irregular surface, was present on the ventral extremity of the spleen. The incision was extended caudad to exteriorize the mass, which hemorrhaged during handling. The greater omentum contained multiple dark red masses measuring up to 1.5 cm in diameter; a well-demarcated, firm, raised, tan mass, 3 cm in diameter, was found in the right medial lobe of the liver.

Hemangiosarcoma was strongly suspected. Treatment options included splenectomy with or without adjunctive chemotherapy; however, no chemotherapeutic regime has been described for pet pigs. Because of the poor prognosis associated with metastasized hemangiosarcoma in other species and the clinical signs present in this case, the pig was euthanized at surgery. The splenic mass was cavitated, containing blood clots and what appeared to be hemosiderin. Samples of the splenic mass, the hepatic mass, and splenic parenchyma were collected, placed in 10% buffered formalin, and submitted for histopathologic examination.

The microscopic examination was suggestive of splenic hemangiosarcoma, but the diagnosis was not confirmed, as neoplastic endothelial cells were not evident in the available section. The slide had been prepared from an area of hematoma formation and massive necrosis, which may occur with splenic torsion, as well as with hemangiosarcoma. The lesion was aged at approximately 72 h, consistent with the onset of clinical signs. Although there was no histological evidence of malignancy, hemangiosarcoma remained the primary diagnosis, on the basis of the apparently metastatic lesions in the omentum and the lack of gross evidence of a splenic torsion.

On microscopic examination, the hepatic mass appeared to be a primary hepatocellular tumor: hepatocytes were arranged in sheets and contained intracellular lipid vacuoles. The final diagnosis was hepatocellular carcinoma.

Neoplasms have not been reported in the potbellied pig in North America. Both hepatic and splenic tumors have been reported in domestic pigs; namely, hepatocellular carcinomas, which are uncommon (1), but have been reported in pigs fed diets of 1 ppm of aflatoxin (these are invasive and generally late to metastasize, with the most common sites of metastasis being the lung and hepatic lymph nodes) (2); primary hepatocellular tumors (3); hepatic hemangioma (4); malignant fibrous histiocytoma of the spleen (5); and splenic hamartoblastoma (6). The splenic tumor in this case appears to have behaved like hemangiosarcomas in other species, which are malignant neoplasms originating from vascular endothelial tissue and are characteristically aggressive and early to metastasize; they have not been described previously in pigs. The tumor was large, occupying much of the abdominal cavity. The blood clots in the peritoneal cavity and hemosiderin in the tumor indicated recent intraperitoneal hemorrhage. Masses that appeared to be metastases were obvious throughout the greater omentum.

The lethargy observed in this animal might have been associated with several factors. The size of the splenic tumor and the space that it occupied may have caused pain, and intraperitoneal hemorrhages probably resulted in anemia. Preoperative hematologic analysis was not performed, owing to the difficulty in obtaining a blood sample without anesthesia. The hepatocellular carcinoma was relatively small and discrete. Although the hepatic lymph nodes were not grossly enlarged in this pig, metastasis of the hepatic tumor cannot be ruled out, as the lungs were not examined. Clinical signs associated with hepatocellular carcinomas are generally related to the size of the primary tumor and the extent of damage to the liver, rather than to metastases (2). The small size and discrete nature of this hepatic tumor make it an unlikely cause of the clinical signs.

This case demonstrates several challenges associated with treating potbellied pigs. Their behavior is significantly different from that of other companion animals, and physical examination is often limited in those pigs unaccustomed to handling. When frightened, pigs squeal and struggle if restrained (7). Inability to perform a physical examination not only makes diagnosis difficult, but also limits the value of an annual health examination, such as is performed in most companion animal species. In this case, inability to palpate the pig's abdomen without anesthesia prevented detection of the abdominal mass. As literature on potbellied pigs is sparse, and practitioners must extrapolate from both production pig literature and companion animal medicine, many practitioners are reluctant to treat this species. Potbellied pigs suffer from many of the same diseases as production pigs (8). Large animal practitioners are more familiar with these conditions, but owners expect potbellied pigs to be handled like pets. The level of veterinary care and diagnostic procedures should reflect their status as companion animals, and many owners prefer to have small animal practitioners treat their potbellied pigs. Small animal veterinarians have been advised to diagnose and treat potbellied pigs as if they were dogs (7,9); however, anatomical and behavioral differences must be considered.

Potbellied pigs were first introduced to North America in 1985 and have become popular as pets (9). Their life span is not known due to their recent introduction to this continent; however, it is believed to be up to 20 y. With improvements in husbandry and nutrition, these animals are living longer lives and developing age-related diseases, similar to those in other species. Although the practitioner can extrapolate information from companion animal literature, many drugs and treatment protocols have not been used in pigs, and it may be challenging to gain the IV access required for many treatments. Thick skin, subcutaneous fat deposits, and fragile veins make venous catheterization difficult, and conscious pigs are easily stressed by the restraint required for this procedure (10).

As the population of potbellied pigs in North America ages, it is likely that neoplastic disease will continue to occur, and it is important for practitioners to consider neoplasms when examining geriatric pet pigs. Treatment regimes for neoplastic disease in potbellied pigs may be described in the future, as more cases are diagnosed and clients expect the same level of care given to other companion animals.