Signalment:  

12-year-old, male, castrated, West Highland white terrier dog (Canis familiaris).A palpable intestinal mass was found on routine examination. Exploratory laparatomy and intestinal resection and anastamosis were performed. The mass was fixed in 10% formalin and submitted for histologic examination.

Gross Description:  

Examination of the fixed tissue revealed large, cystic structures expanding the intestinal wall. The cysts were filled with gelatinous, clear material (mucus).

Histopathologic Description:

In sections of jejunum examined, a sparsely cellular mass infiltrates the base of the mucosa, is present in the lamina muscularis, extends to the tunica muscularis and forms expansile mucus-filled, cysts. They diffusely distort the lamina muscularis and submucosa. In some sections, aggregates of mineralized debris are seen in the center of the mucus-filled cysts. Neoplastic cells are columnar to cuboidal or flattened, form small nests or line cyst walls, and are supported by fine to moderately abundant fibrous stroma. Cell layers 1-6 cells thick surround lakes of mucus that at times contain small clusters of cells. Cytoplasm is eosinophilic and faintly granular. Nuclei are round and contain reticular chromatin and one to three distinct nucleoli. Frequently, cells are rounded with abundant foamy amphophilic cytoplasm that peripheralizes the nucleus (signet ring cells). Mitoses (sometimes bizarre) are rare. Neoplastic cells are present in the most terminal sections of the resected segment of intestine examined. In some sections, the surface epithelium is eroded, hemorrhagic and contains rod-shaped bacteria mixed with fibrin. The lamina propria is defined by moderate numbers of neutrophils, few lymphocytes and plasma cells, rare eosinophils and mildly congested blood vessels. Immunohistochemical staining for cytokeratin positively stains enterocytes and neoplastic cells.

Morphologic Diagnosis:  

1. Intestine, jejunum: Mucinous adenocarcinoma.
2. Intestine, jejunum: Moderate, sub-acute, multifocal, fibrinosuppurative, erosive enteritis with bacterial rods.

Condition:  

Mucinous adenocarcinoma

Contributor Comment:  

Intestinal neoplasms in the dog are rare, with primary intestinal neoplasms being more common than metastatic disease.(2,4,6) Primary intestinal neoplasms may arise from the following tissues: epithelium, neuroendocrine cells, mesenchyme (vascular, connective tissue, adipose, or peripheral nerve sheath tumors), lymphoid tissues, extramedullary plasma cells, mast cells, smooth muscle, or serosa.(4) Colonic masses are more frequently encountered, with papillomatous lesions making up the majority of colon tumors.(6) Most are reported to be scirrhous and mucus producing.(2) Other gross lesions can appear as mural thickening, areas of ulceration, white and fibrous tissue, or serosal plaque-like masses.

Transmural invasion is a differentiating feature between adenomatous hyperplasia and neoplasia.(2) Histologic patterns reported include acinar, papillary, solid, carcinoid, and mucinous (including signet-ring cell carcinoma).(6) Signet-ring cells are cells filled with copious mucin that perpheralizes the nucleus. No prognostic behavior has been attributed to the difference in histological pattern.

Intestinal adenocarcinomas metastasize widely via lymphatics, and, at times, via direct serosal implantation.(2) Serosal implantation can cause lymphatic blockage, leading to ascites.(2) Rare manifestations of metastasis include cutaneous masses and pseudomyxoma peritonei.(1,5) Cutaneous lesions in a dog with duodenal adenocarcinoma and masses in numerous organs consisted of undifferentiated, non-cohesive islands of round to polygonal cells.(5) In this case, definitive diagnosis of the undifferentiated mass was supported by identification of a primary intestinal lesion and positive staining of metastases by pancytokeratin, periodic acid Schiff, and Alcian blue. A single case of pseudomyxoma peritonei describing mucin accumulation in the peritoneum and peritoneal cavity was reported in 2003.(1) Mucin was trapped in fibrous reticulin mesh in tissue from the peritoneum and mesenteric fat and in fibrous septa in tissue from the diaphragm. To date, no pathologic basis for mucin accumulation has been identified in this patient or in humans affected by a similar condition.

JPC Diagnosis:  

Small intestine: Adenocarcinoma, mucinous type.

Conference Comment:  

The contributor provides a fairly straightforward case of mucinous adenocarcinoma in the jejunum of a dog, pairing it with a succinct synopsis of the entity. The conference moderator cautioned participants to carefully consider adenocarcinoma, which in dogs is more common than intestinal adenoma, whenever glands are present in the submucosa, tunica muscularis or serosa, even in cases with a predominance of histologically bland neoplastic cells; tumor cells in intestinal adenocarcinoma can be well-differentiated, a finding that may vary regionally within a given malignant neoplasm. This case is typical in that intestinal neoplasms of epithelial origin are more commonly found in males than females, whereas the opposite is true for nonepithelial intestinal tumors. Of note, adenocarcinomas in dogs are more common in the large intestine than in the small intestine.(3)

The following summary of the World Health Organization classification of intestinal adenocarcinoma is provided with the caveats that a given tumor often exhibits more than one growth pattern, and as mentioned by the contributor, growth pattern is not correlated with prognosis:(3)

Classification of Intestinal Adenocarcinoma in Domestic Animals
Type	Microscopic Features
Acinar (tubular)	Acini and tubules replace the intestinal mucosa
Papillary (polypoid, cribriform)	Multiple layers of anaplastic columnar cells line papillary projections
Mucinous (colloid, mucoid)	Acinopapillary growth with at least 50% of the tumor replaced by extracellular mucin
Signet ring cell (goblet cell, intracellular mucinous)	At least 50% of the neoplasm is composed of signet-ring cells with intracytoplasmic mucin that peripheralizes crescentic nuclei; lacks gland formation; severe desmoplasia
Undifferentiated	Solid sheets of anaplastic or pleomorphic cells without squamous or glandular differentiation
Adenosquamous (adenoacanthoma, adenocarcinoma with squamous differentiation)	Gland-forming adenocarcinoma with areas of squamous differentiation and variable keratinization

References:

1. Bertazzolo W, Roccabianca P, Crippa L, Caniatti M: Clinicopathological evidence of pseudomyxoma peritonei in a dog with intestinal mucinous adenocarcinoma. J Am Anim Hosp Assoc 39:72-75, 2003
2. Brown CC, Baker DC, Barker IK: Alimentary system. In: Jubb, Kennedy, and Palmers Pathology of Domestic Animals, ed. Maxie MG, 5th ed., vol. 2, pp. 117-120. Saunders Elsevier, Philadelphia, PA, 2007
3. Head KW, Cullen JM, Dubielzig RR, Else RW, Misdorp W, Patnaik AK, Tateyama S, van der Gaag I: Histological Classification of Tumors of the Alimentary System of Domestic Animals, 2nd series, vol. X, ed. Schulman YF, pp. 89-94. Armed Forces Institute of Pathology (in cooperation with the ARP and the WHO Collaborating Center for Worldwide Reference on Comparative Oncology), Washington, DC, 2003
4. Head KW, Else RW, Dubielzig RR: Tumors of the intestines. In: Tumors in Domestic Animals, ed. Meuten DJ, 4th ed., pp. 461-468. Iowa State Press, Ames, IA, 2002
5. Juopperi TA, Cesta M, Tomlinson L, Grindem CB: Extensive cutaneous metastases in a dog with duodenal adenocarcinoma. Vet Clin Pathol 32:88-91, 2003
6. Patnaik AK, Hurvitz, AI, Johnson GF: Canine intestinal adenocarcinoma and carcinoid. Vet Pathol 17:149-163, 1980

A virtual slide is not available for this case.

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2-1. Adenocarcinoma, mucinous type, jejunum

2-2. Adenocarcinoma, mucinous type, jejunum

2-3. Adenocarcinoma, mucinous type, jejunum

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