Case 8-1. Stomach. The gastric rugal folds are hypertrophied.

Gross Pathology: The gastric wall was thickened and displayed a nodular surface with a whitish discoloration.

Laboratory Results: Parasitological investigation of feces: Cryptosporidium serpentis

Contributor’s Diagnosis and Comment: Stomach: Chronic, diffuse, moderate to severe epithelial hyperplasia and hypertrophy with moderate Cryptosporidia infestation; moderate to marked hypertrophy of the gastric wall.

The entire gastric wall was massively thickened. The surface epithelium was hyperplastic and hypertrophic with dilated glandular tubules. The lamina muscularis was also hypertrophic. Within the tunica mucosa and tunica submucosa, there were focal small infiltrates of lymphocytes and macrophages with moderate edema and lymphangiectasia. Randomly distributed, small (approximately 2 m m diameter) basophilic, spherical to elliptic bodies (suggestive of Cryptosporidium sp.) were attached to the surface of epithelial cells, often surrounded by scant amounts of mucinous material.

Cryptosporidia are small (2-6 m m) Apicomplexan protozoan parasites found on the surface of gastrointestinal and respiratory tract epithelium in mammals, birds and reptiles. Diarrhea is the main clinical sign in infected mammals. Birds can also develop respiratory signs. In snakes, the most striking clinical manifestation in chronic infections is swelling of the stomach. This is due to a hypertrophic gastropathy characterized by a massive thickening of the whole gastric wall. With progressive narrowing of the stomach, the animal is unable to digest its food and, although the appetite may remain relatively hearty, affected snakes regurgitate undigested mice one to three days after feeding. Histologically, hypertrophy and hyperplasia of the surface epithelium are typical findings, as well as edema of the lamina propria and lamina muscularis. Various stages of cryptosporidia are attached to the brush border microvilli of epithelial cells lining the gastric pits and gastric lumen. Associated inflammatory infiltration and necrosis can be observed occasionally.

Infections with cryptosporidia are easily transmissible between hosts belonging to the same vertebrate class, whereas transmission between different species is only rarely observed. Cryptosporidium serpentis was considered to be the only valid species in reptiles, although there is evidence that there may be as many as five species or subspecies of Cryptosporidium infecting reptiles. Infection with Cryptosporidium serpentis may be asymptomatic and infected snakes may excrete oocysts in the feces for years without obvious clinical signs. If animals are subjected to stress of capture, transportation over long distances, or poor husbandry conditions, the infection may lead to severe clinical signs and death.

Cryptosporidia have monoxenous life cycles where all stages of development (asexual and sexual) occur within one host. Once ingested, oocysts excyst in the gastrointestinal tract and release the infective sporozoites. The freed sporozoites attach to epithelial cells where they become enclosed within parasitophorous vacuoles and develop to trophozoites. The trophozoites then undergo asexual proliferation by merogony. Sexual reproduction occurs by gametogony. The zygotes undergo further asexual development leading to the production of sporulated oocysts containing 4 sporozoites.

Cryptosporidium oocysts excreted with feces can be demonstrated by flotation. In fecal smears, it is possible to detect the oocysts with acid-fast stains. Oocysts stain bright red while bacteria, yeasts and other fecal debris only take up the counter stain. Immunohistochemistry may also be used. For further characterization and identification of different Cryptosporidium spp., various biochemical and molecular methods should be applied (multilocus enzyme electrophoresis, PCR).

AFIP Diagnosis: Stomach: Mucosal neck epithelial cell hyperplasia and hypertrophy, diffuse, moderate, with lamina proprial and submucosal edema, granular cell loss, and superficial protozoal organisms, Dumeril’s ground boa (Acrantophis dummerili), snake, etiology consistent with Cryptosporidium spp.

Conference Comment: Ultrastructurally, cryptosporidia are unique in their intracellular, but extracytoplasmic, location within parasitophorous vacuoles formed by a continuous covering of microvillous membrane of the intestinal mucosa. The parasites contain a unique attachment or “feeder” organelle that is thought to function in the uptake of nutrients from the host cell. This organelle is prominent at the base of the parasitophorous vacuole. The parasite pellicle forms a close, electron-dense adhesion zone where the outer microvillous membrane fuses with the epithelial plasma membrane.

Contributor: Justus-Liebig-Universität Giessen, Institut für Veterinär-Pathologie, Frankfurter Strasse 96, D-35392 Giessen, Germany

References: 1. Barker IK, Van Dreumel AA, Palmer N: The alimentary system. In: Pathology of Domestic Animals, ed. Jubb KVF, Kennedy PC, Palmer N, 4^th ed., vol. 2, pp. 312-315. Academic Press, New York, NY, 1993

2. Gasser RB, O’Donoghue P: Cryptosporidium. Int J Parasitol 29:1379-1413, 1999

3. O’Donoghue PJ (1995): Cryptosporidium and cryptosporidiosis in man and animal; Int J Parasitol 25(2):139-195, 1995

4. Taylor MA, Geach MR, Cooley WA: Clinical and pathological observations on natural infections of cryptosporidiosis and flagellate protozoa in leopard geckos (Eublephans macularius). Vet Rec 145:695-699, 1999

CASE II – N55 (AFIP 2744062)

Signalment: 11-year-old, female, Siamese cat, feline

History: Appearance, 1-year ago, of four pruriginous, well delineated, slightly raised, crusty, alopecic cutaneous lesions. Three were in the cervical region (ventrally and dorsally), one on the forelimb. The size (from 0.5 to 2 cm in diameter) and the number of these cutaneous plaques did not progress during this time and they were unresponsive to corticosteroid therapy. Recurrent psychogenic alopecia had also been observed in this cat for 5 years. The animal was otherwise healthy.

Gross Pathology: Two raised, well-demarcated, cutaneous plaques were submitted for histopathology

Laboratory Results: None.

Contributor’s Diagnosis and Comment: Skin: Squamous cell carcinoma in situ (Bowen’s disease), Siamese, feline.

One or two sharply demarcated cutaneous plaques are present on the slides that fulfill the published histologic criteria for the diagnosis of squamous cell carcinoma in situ:

1) Cellular atypia, including cells with pleomorphic or abnormally large nuclei 2) Mitotic figures more than three cell layers above the basal cell layer

3) Dyskeratotic keratinocytes

4) Disorderly maturation of the epidermis

Neoplastic keratinocytes are enlarged with pale, often vacuolated cytoplasm. The nucleus displays one or more prominent nucleoli. Neoplastic cells are present in the stratum basale and extend throughout the entire thickness of the stratum spinosum, contributing to epidermal and follicular infundibular thickening. Ortho- and parakeratotic hyperkeratosis is minimal to moderate. Rare cells appear to have more than one nucleus. Although invasion of the dermis was considered in some areas, the basement membrane appeared to be intact with PAS stain. The lesions are variably ulcerated, covered by a fibrinonecrotic exudate and infiltrated by mixed inflammatory cells.

Multicentric squamous cell carcinoma in situ has recently been reported in cats and has been referred to as Bowen’s disease owing to its histological resemblance to this disease entity in human beings.

First described by Bowen in 1912, the condition in man consists of indolent, scaly, erythematous, often solitary, plaques involving predominantly skin that is unexposed to sunlight. Bowen’s lesions differ clinically from actinic keratosis, which is located in sun-exposed areas, however, similar microscopic changes are observed in both entities.

In cats, the lesions are usually multifocal, but are occasionally solitary. They occur at any site in the skin and are not associated with sun exposure. They are observed in middle-aged to older cats. Surgical excision is curative, but new lesions may develop at different sites. If not excised, in situ lesions may progress to invasive squamous cell carcinoma with a low potential for metastasis.

AFIP Diagnosis: Haired skin: Squamous cell carcinoma in situ, with minimal multifocal dermal invasion, cat, Siamese, feline.

Conference Comment: Cutaneous squamous cell carcinoma is one of the most common neoplasms of cats. Feline multicentric squamous cell carcinoma in situ is a comparatively rare condition that is distinguished from actinic keratosis primarily by clinical presentation. Actinic keratosis affects sun-exposed, sparsely haired, lightly pigmented areas of the skin whereas the lesions of feline multicentric squamous cell carcinoma in situ occur in the haired, pigmented regions.

Although feline squamous cell carcinoma in situ is histomorphologically similar to the bowenoid type of squamous cell carcinoma in man, the disease in cats is not identical to Bowen’s disease and the term Bowen’s disease is defined differently by different authors. Therefore, this term is best avoided.

While most conference attendees agreed with the diagnosis of squamous cell carcinoma in situ, several had evidence of focal, limited dermal invasion. Feline multicentric squamous cell carcinoma in situ has been reported to develop into invasive squamous cell carcinoma in 25-27% of the cats, but has not been reported to metastasize. Papillomavirus antigen has been demonstrated in some of these feline lesions.

Contributor: Laboratoires Pfizer, Centre de Recherche, BP 159, Amboise Cédex, 37401, France

References: 1. Baer KE, Helton K: Multicentric squamous cell carcinoma in situ resembling Bowen’s disease in cats. Vet Pathol 30:535-543, 1993

2. Rees CA, Goldschmidt MH: Cutaneous horn and squamous cell carcinoma in situ (Bowen’s disease) in a cat. J Amer Anim Hosp Assoc 34:485-486, 1998

3. Rosai J: The skin. In: Ackerman’s Surgical Pathology, 8^th ed., vol. 1, p.109. Mosby, Baltimore, MD, 1996

4. Scott DW, Miller WH, Griffin CE: Neoplastic and non-neoplastic tumors. In: Muller & Kirk’s Small Animal Dermatology, 6^th ed, pp. 1258-1259. WB Saunders Company, Philadelphia, PA, 2001

5. Walder EJ, Gross TL: Neoplastic diseases of the skin. In: Veterinary Dermatopathology, ed. Gross TL, Ihrke PJ, Walder EJ, pp. 340-341. Mosby Year Book, Baltimore, MD, 1992

6. Yager JA, Wilcock BP: Solid epidermal tumours. In: Color Atlas and Text of Surgical Pathology of the Dog and Cat, pp. 253-256. Wolfe Publishing, Spain, 1994

CASE III – V9721159 (AFIP 2643031)

Signalment: Four-year-old, castrated male, domestic shorthair, feline, Felis catus

History: The owner noticed a large mass on the ventral abdomen. There were no other signs of illness.

Gross Pathology: The surgical specimen included skin and subcutis with an ulcerated, firm, broad-base pedunculated mass 7.0 x 4.5 x 4.0 cm. The ulcer was 5.0 cm in greatest dimension. The cut-surface of the mass was solid, white, bulging and slightly irregular. The cutaneous adnexa were widely separated and in some regions there were poorly defined blue-gray zones immediately below the skin surface.

Laboratory Results: None.

Contributor’s Diagnosis and Comment: Feline sarcoid-like neoplasm, cause not known.

Where the neoplastic cells in the dermis appose the epidermis, there is marked irregular epidermal acanthosis with very long rete ridges and epidermal orthokeratotic hyperkeratosis. Whereas there is only a trace of epidermal melanin distant to the spindle-shaped neoplastic cells, there are foci of melanin clumping in the long rete ridges and some hair follicles. In several small foci, the basement membrane of the epidermis, rete ridges and hair follicles is indistinct with squamous cells appearing to blend with the adjacent tumor cells. This “blending” was more apparent in a PAS-stained section.

Where melanin clumping occurred and basement membrane appeared disrupted, some of the adjacent spindle-, stellate-, and dendritic-shaped tumor cells contained melanin. Further away, none of the tumor cells had melanin.

The majority of the neoplastic cells stained lightly positive for S-1OO protein, but some scattered cells stained intensely positive. It could not be determined with certainty whether the melanin-containing cells in the dermis stained positively for S-1OO protein, raising the possibility of those cells being melanophages. The normal melanocytes within the dermis stained intensely positive for S-1OO and vimentin, but negative for low and high molecular weight cytokeratins. The neoplastic cells stained intensely positive for vimentin and negative for the cytokeratins.

There were numerous scattered mast cells surrounded by an artifactual shrinkage halo. These cells stained PAS-positive and had metachromatic granules in a Giemsa-stained section. Most high power fields of the tumor had 40-80 scattered mast cells.

While it is tempting to classify this neoplasm as a benign fibromatous melanoma, the cells have not been proven to be of melanocytic origin. The cells in the dermis that contained melanin may have been melanophages. Electron microscopic findings support the presence of fibroblast-like cells and scattered mast cells. In human beings, the cells of desmoid fibromatosis are S-1OO negative and actin positive, in contrast to the spindle-, stellate-, and dendritic-shaped cells in this lesion.

The cat was healthy, with no tumor recurrence, seven months after surgery.

AFIP Diagnosis: Haired skin: Fibropapilloma, domestic shorthair, feline.

Conference Comment: Fibropapilloma is a term used to refer to a benign fibroblastic proliferation with overlying acanthosis, hyperkeratosis and prominent rete ridge formation. In veterinary medicine, these tumors are generally attributed to papillomavirus infections. Fibropapillomas with papillomavirus association have been reported in cattle, horses, donkeys, mules, cervids and a pronghorn antelope. In cattle, at least three different bovine papillomaviruses cause fibropapillomas and a number of studies have provided evidence that these bovine papillomaviruses also play a role in the development of equine sarcoids.

Feline cutaneous fibropapillomas with histologic findings similar to the virus-associated fibropapillomas are occasionally seen among submissions to veterinary diagnostic laboratories. Recently in a study of 23 feline fibropapillomas, all of the 17 tumor specimens that had amplifiable DNA tested positive for papillomavirus DNA by polymerase chain reaction. The tumors in this study occurred most commonly in young cats and were found primarily on the head, neck and digits. Local recurrence of the tumors occurred in 7 of the 18 cats for which follow up information was available.

Contributor: Marshfield Laboratories, Veterinary Division, 1000 North Oak Avenue, Marshfield, WI 54449-5795

References: 1. Schulman FY, Krafft AE, Janczewski T: Feline cutaneous fibropapillomas (sarcoid): clinicopathologic findings and association with papillomavirus infection. Vet Pathol 37(5):532, 2000 [abstract]

2. Scott DW, Miller WH, Griffin CE: Neoplastic and non-neoplastic tumors. In: Muller & Kirk’s Small Animal Dermatology, 6^th ed, p. 1285. WB Saunders Company, Philadelphia, PA, 2001

3. Yager JA, Scott DW, Wilcock BP: The skin and appendages. In: Pathology of Domestic Animals, ed. Jubb KVF, Kennedy PC, Palmer N, 4^th ed., vol. 1, pp. 708-710. Academic Press, New York, NY, 1993

4. Yager JA, Wilcock BP: Epithelial tumours. In: Color Atlas and Text of Surgical Pathology of the Dog and Cat, pp. 292-293. Wolfe Publishing, Spain, 1994

CASE IV – 9517-96 (AFIP 2739555)

Signalment: Two-year-old, female, thoroughbred, equine

History: The filly had a protruding mass on the cornea and soft tissue masses in the orbit of the left eye 4 months after being treated for uveitis. The left eye was exenterated and submitted for histopathologic examination.

Gross Pathology: The enucleated eyeball had a corrugated dark brown mass covering the cornea, disrupting the uvea and obliterating the anterior and posterior chambers. The vitreous body contained two large solid masses and blood-clot-like material. The periocular fat and the base of the optic nerve also contained nodular or poorly defined flat masses.

Laboratory Results: Not available.

Contributor’s Diagnosis and Comment: Malignant rhabdoid tumor, left eye, thoroughbred, equine.

Microscopically, the neoplastic mass was composed of sheets of large polygonal cells with abundant eosinophilic cytoplasm. Many cells contained a paranuclear globular inclusion. Most neoplastic cells had large, vesiculated, indented, eccentric nuclei. Mitotic figures were many. Large areas of necrosis and hemorrhage were frequently seen in the neoplastic masses. Immunohistochemical staining revealed that the globular inclusions in the neoplastic cells were strongly positive with vimentin antibody, weakly positive with cytokeratin and GFAP antibodies, but negative for desmin and actin. Electron microscopically, the globular inclusion was made up of large whorls of intermediate filaments. From histologic, ultrastructural and immunohistochemical findings, the tumor was consistent with malignant rhabdoid tumor.

Malignant rhabdoid tumor is highly malignant and a primary tumor of the kidney in infants. Histogenesis of malignant rhabdoid tumor is unknown.

AFIP Diagnosis: Eye: Malignant rhabdoid tumor, thoroughbred, equine.

Conference Comment: Rhabdoid tumors are highly aggressive tumors that are usually found in the kidneys of children, but have been described in many tissues. The presence of abundant eosinophilic cytoplasm led to the original misconception that these tumors were of skeletal muscle origin and thus were given the term “rhabdoid”. A diagnosis of rhabdoid tumor is not specific as to cell of origin. Rather, the diagnosis is based on characteristic histologic, immunohistochemical and ultrastructural characteristics and the exclusion of other neoplasms with rhabdoid inclusions. Histologically, rhabdoid tumors are composed of sheets or clusters of large tumor cells with vesicular nuclei, a single prominent nucleolus and abundant glassy eosinophilic cytoplasm that often forms a globular inclusion and peripheralizes the nucleus. The globular inclusions are composed of whorls of intermediate filaments. In the veterinary literature, rhabdoid tumors have been reported in the stomach of an orangutan, the brain of a dog and this horse eye. The latter two involved the CNS and were both multifocally positive for GFAP.

Contributor: University of Kentucky, Livestock Disease Diagnostic Center, 1429 Newtown Pike, Lexington, KY 40511

References: 1. Hong CB, VanMeter PW, Latimer CL: Malignant rhabdoid tumour in the orbit of a horse. J Comp Path 121:197-201, 1999

2. Schauer G, Moll R, Walter JH, Rumpelt HJ, Goltenboth R: Malignant rhabdoid tumor in the gastric wall of an aged orangutan (Pongo pygmaeus). Vet Pathol 31(5):510-517, 1994

3. Steele KE, Schulman FY, Mena H, Strimple EO: Rhabdoid tumor in the brain of a dog. Vet Pathol 34(4):359-363, 1997

*Sponsored by the American Veterinary Medical Association, the American College of Veterinary Pathologists and the C. L. Davis Foundation.