History
A 14-year-old spayed female Vietnamese potbellied pig underwent an exploratory laparotomy after recurrent episodes of anorexia and severe abdominal distention over an approximately 5-year period. The latest episodes had occurred in the 24- to 48-hour period before surgery.
Clinical and Gross Findings
The pig had undergone a similar procedure 5 years earlier because of an episode of intestinal obstruction. During that procedure, a colonic mass was resected and diagnosed as a colonic adenocarcinoma. Subsequent episodes of anorexia and abdominal distention continued to occur after the first surgical procedure. The second exploratory laparotomy revealed another colonic mass located at the same site as the previous tumor; this mass had multiple firm nodules along the spiral colon. Euthanasia by means of an IV barbiturate overdose while the pig was anesthetized was elected owing to the poor prognosis. Grossly, the most important changes were limited to the colon. The serosa of the spiral colon had multiple, white, firm, 1- to 2-cm-diameter nodules distributed along its surface. A white, firm, irregular, transmural mass measuring 6 × 5 × 6 cm expanded the spiral colon and partially obstructed its lumen (Figure 1). On cut surface, the mass was white with multiple hemorrhagic foci. A similar mass measuring 2 cm in diameter was observed adjacent to the first mass. The intestinal loops cranial to the mass were distended by gas. The lungs were diffusely dark red and moist, and a small amount of white froth was observed in the trachea (edema). Fresh samples of the large intestine were submitted for testing for Salmonella enterica subsp enterica with a PCR assay.
Photograph of the colonic mucosal surface (asterisks) of a 14-year-old Vietnamese potbellied pig that had had multiple episodes of anorexia and severe abdominal distention over an approximately 5-year period. The colonic mucosa is expanded by a white, firm mass (arrows) with areas of hemorrhage (arrowhead).
Citation: Journal of the American Veterinary Medical Association 251, 12; 10.2460/javma.251.12.1387
Photograph of the colonic mucosal surface (asterisks) of a 14-year-old Vietnamese potbellied pig that had had multiple episodes of anorexia and severe abdominal distention over an approximately 5-year period. The colonic mucosa is expanded by a white, firm mass (arrows) with areas of hemorrhage (arrowhead).
Citation: Journal of the American Veterinary Medical Association 251, 12; 10.2460/javma.251.12.1387
Photograph of the colonic mucosal surface (asterisks) of a 14-year-old Vietnamese potbellied pig that had had multiple episodes of anorexia and severe abdominal distention over an approximately 5-year period. The colonic mucosa is expanded by a white, firm mass (arrows) with areas of hemorrhage (arrowhead).
Citation: Journal of the American Veterinary Medical Association 251, 12; 10.2460/javma.251.12.1387
Formulate differential diagnoses from the history, clinical findings, and Figure 1—then turn the page →
Histopathologic, Immunohistochemical, and Laboratory Findings
Multiple tissue samples from the gastrointestinal tract, mesenteric lymph nodes, lungs, liver, kidneys, spleen, skeletal muscles, adrenal glands, thyroid gland, and brain were collected, fixed in neutral-buffered 10% formalin, and routinely processed for histologic examination. Histologically, the colonic masses were composed of small groups of neoplastic epithelial cells supported by preexisting tissue and a prominent fibrous connective and collagenous stroma (Figure 2). Neoplastic cells were present throughout the submucosa, muscle layers, and serosal surface and were arranged in small or large groups with abundant, round, foamy cytoplasm containing faintly basophilic, mucinous material that reacted with Mayer mucicarmine special stain. Nuclei were round and small and had dense chromatin with 1 evident nucleolus. Multifocal well-circumscribed infiltrations of epithelioid macrophages and multinucleated giant cells with fewer lymphocytes and plasma cells were observed in the submucosa and were always associated with concentric needle-shaped cholesterol clefts. A diffuse, mild to moderate lymphoplasmacytic and eosinophilic inflammatory infiltrate was observed in the overlying colonic lamina propria. Immunohistochemical analysis revealed that the neoplastic cells were strongly immunoreactive for pancytokeratin (AE1/AE3). Pulmonary alveolar edema was confirmed histologically, and no metastases or other changes were identified in other organs. The result of the PCR assay of large intestine samples was negative for S enterica subsp enterica.
Photomicrographs of sections of colon obtained from the pig in Figure 1. A—Multiple small groups of neoplastic cells have expanded the submucosa (arrowheads) and muscle layers (arrow). H&E stain; bar = 500 μm. B—Neoplastic cells are arranged in large or small groups embedded in a dense desmoplastic stroma. H&E stain; bar = 100 μm. C—The cytoplasm of the neoplastic cells contains a mucinous secretion, which is stained red. Mayer mucicarmine stain; bar = 100 μm. D—The neoplastic cells have strong cytoplasmic immunoreactivity for pancytokeratin (brown). Immunohistochemical reaction specific for pancytokeratin (AE1/AE3); bar = 50 μm.
Citation: Journal of the American Veterinary Medical Association 251, 12; 10.2460/javma.251.12.1387
Photomicrographs of sections of colon obtained from the pig in Figure 1. A—Multiple small groups of neoplastic cells have expanded the submucosa (arrowheads) and muscle layers (arrow). H&E stain; bar = 500 μm. B—Neoplastic cells are arranged in large or small groups embedded in a dense desmoplastic stroma. H&E stain; bar = 100 μm. C—The cytoplasm of the neoplastic cells contains a mucinous secretion, which is stained red. Mayer mucicarmine stain; bar = 100 μm. D—The neoplastic cells have strong cytoplasmic immunoreactivity for pancytokeratin (brown). Immunohistochemical reaction specific for pancytokeratin (AE1/AE3); bar = 50 μm.
Citation: Journal of the American Veterinary Medical Association 251, 12; 10.2460/javma.251.12.1387
Photomicrographs of sections of colon obtained from the pig in Figure 1. A—Multiple small groups of neoplastic cells have expanded the submucosa (arrowheads) and muscle layers (arrow). H&E stain; bar = 500 μm. B—Neoplastic cells are arranged in large or small groups embedded in a dense desmoplastic stroma. H&E stain; bar = 100 μm. C—The cytoplasm of the neoplastic cells contains a mucinous secretion, which is stained red. Mayer mucicarmine stain; bar = 100 μm. D—The neoplastic cells have strong cytoplasmic immunoreactivity for pancytokeratin (brown). Immunohistochemical reaction specific for pancytokeratin (AE1/AE3); bar = 50 μm.
Citation: Journal of the American Veterinary Medical Association 251, 12; 10.2460/javma.251.12.1387
Morphologic Diagnosis and Case Summary
Morphologic diagnosis and case summary: colonic mucinous adenocarcinoma (spiral colon) in a Vietnamese potbellied pig.
Comments
The gross, histologic, histochemical, and immunehistochemical findings for the pig of the present report were consistent with the diagnosis of colonic mucinous adenocarcinoma.1–11 Diagnostic confirmation was achieved by the widespread positive immunoreaction of neoplastic cells for pancytokeratin.1,2 Intestinal adenocarcinomas in domestic pigs have been rarely reported but appear to develop more often in potbellied pigs.1–3 This apparent breed predilection may be explained by the fact that domestic pigs are typically slaughtered at an early age, whereas potbellied pigs are considered companion animals in the United States and attain old age, consequently increasing their chances for development of intestinal adenocarcinomas.2 Although aging has been implicated as an important factor for the development of intestinal adenocarcinomas in pigs and uterine neoplasia in miniature pet pigs,4,5 other factors, such as genetic predisposition, diet, and environmental conditions may also influence the development of these tumors.3,6 Similar to the case described in the present report, the most common clinical signs in affected individuals, regardless of species, include anorexia, weight loss, vomiting, diarrhea, colic, ascites, and anemia attributable to ulceration and chronic blood loss.2,7–9
Intestinal adenocarcinomas can affect various areas of the gastrointestinal tract in pigs, such as the jejunum,4,6 colon,3 and cecum.10 These tumors are locally invasive and typically incite a strong desmoplastic reaction that causes a focal constriction and luminal stenosis of the affected intestinal loop.9 Intestinal adenocarcinomas can metastasize to regional lymph nodes, lungs, and liver.2,3,10,11 The pig of the present report previously had an intestinal adenocarcinoma that was resected 5 years prior. It is unknown whether the resection was complete at that time, but recurrence and metastasis may be common with intestinal adenocarcinoma.1,2,9 Thus, the multiple masses and nodules observed during necropsy may have been related to recurrence or extension of the previously resected neoplasm in this pig. Mucinous adenocarcinoma is a subtype of intestinal adenocarcinoma in which at least 50% of the neoplastic cells produce mucin.1,2,9 Mucinous adenocarcinomas in domestic pigs and Vietnamese potbellied pigs have been rarely described,6,10 but other species such as dogs, cats, cattle, ferrets, and primates (including humans) may be affected.7,10–12 Intestinal adenocarcinomas typically have characteristic morphological features that allow for their diagnosis on the basis of results of routine tissue section staining. As observed in the case described in the present report, immunehistochemical analysis for pancytokeratin can be useful in highlighting the distribution of neoplastic cells among the dense desmoplastic reaction produced by the tumor.
For the Vietnamese potbellied pig of the present report, a diagnosis of colonic mucinous adenocarcinoma was made on the basis of gross, histologic, and histochemical findings and was confirmed by the neoplastic cells' pancytokeratin-specific immunoreactivity. The granulomatous inflammatory reaction in the intestine was considered to be secondary to the previous surgical procedure or a reaction to the mucin derived from adjacent neoplastic cells.
Acknowledgments
Dr. Watanabe was a visiting veterinarian in the Department of Pathology, College of Veterinary Medicine, University of Georgia, at the time this case was examined.
References
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