JPC SYSTEMIC PATHOLOGY
Signalment (JPC 2005790): Young broiler chicken
HISTORY: This chicken had multiple ulcerative dermal lesions noted at slaughter.
HISTOPATHOLOGIC DESCRIPTION: Feathered skin: Diffusely, the epidermis is absent (scalding artifact). Multifocally infiltrating and replacing the dermis and subcutis is an unencapsulated, poorly circumscribed, ulcerated, crateriform neoplasm composed of poorly defined cords and islands of polygonal cells on an abundant fibrovascular stroma composed of reactive fibroblasts (desmoplasia) with scattered heterophils, lymphocytes, and plasma cells. Polygonal cells have variably distinct cell borders, an abundant amount of intensely eosinophilic to globular cytoplasm, irregularly oval vesiculate nuclei and one to two prominent nucleoli. Mitoses average one per HPF. Neoplastic cells frequently undergo dyskeratosis, and rarely surround islands of brightly eosinophilic keratin (keratin pearls). Multifocally there are areas of cellular loss (necrosis) and heterophils and macrophages infiltrating adjacent adipose tissue. Focally, there is a hyperplastic feather follicle with abundant keratin surrounded by a thickened epithelium with rare intercellular edema (spongiosis), and mild orthokeratotic hyperkeratosis. Lymphatics are multifocally dilated (edema) and vessels often contain aggregates of heterophils.
MORPHOLOGIC DIAGNOSIS: Feathered skin: Keratoacanthoma, breed unspecified, chicken, avian.
CONDITION: Avian keratoacanthoma
SYNONYMS: Dermal squamous cell carcinoma; squamous epithelioma
- Keratoacanthoma is an uncommon, benign neoplasm primarily seen in young broilers (meat type chickens); rarely seen in older chickens
- Superficially invasive, but does not metastasize
- Seasonal (decrease incidence in summer); spontaneous regression related to molting cycle
- Economic importance - multiple lesions results in carcass condemnation
- Etiology unknown; thought to be viral induced (fowlpox, type C retrovirus)
- Multicentric nodular lesion originates from epithelium, at margin of hyperplastic feather follicles > infiltrates adjacent dermis > enlarges and ulcerates > regresses spontaneously after loss of keratin core > forms a dermal scar
- Has been reproduced in laboratory chickens exposed to topical methylcholanthrene
TYPICAL CLINICAL FINDINGS:
- Nodular to ulcerated, single to coalescing, crateriform skin lesions of the pectoral, dorsopelvic, and femoral feather tracts (pteryla)
TYPICAL GROSS FINDINGS:
- Exo-endophytic, cup-shaped, broad-based neoplasm originating from the feather follicle epithelium
- Crater-shaped coalescing ulcers with raised margins within feather tracts
- Ulcers may contain central core of keratin, cellular debris, and bacteria
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Carcass lesions usually extensively altered by post slaughter de-feathering
- Nodular lesions composed of a central cystic space with a keratinaceous core
- Nests/cords of atypical keratinocytes with hyperplastic and cystic feather follicles
- Ulcerative lesions - keratin filled; lined by squamous epithelium; islands/cords of atypical keratinocytes invade the surrounding fibrous connective tissue
- Adjacent feather follicles - often hyperplastic and hyperkeratotic
- Lymphocytes, heterophils, and macrophages infiltrate the fibrous connective tissue
- Cyst enclosed by a basement membrane with numerous desmosomes between adjacent keratinocytes, which contain tonofibrils or keratohyaline granules; virus particles are not present
- Focal ulcerative dermatitis
- Squamous cell carcinoma: Affects older birds; reported in the crops of a psittacine and a game bird; more invasive
- Subungual keratoacanthoma (I-N31) or “claw bed tumor”, nail bed origin
- Adnexal tumors of follicular origin: Infundibular keratinizing acanthoma (arises from infundibular epithelium), intracutaneous cornifying epithelioma, tricholemmoma, trichofolliculoma, trichoblastoma, trichoepithelioma, and pilomatricoma
- Hamster: Common benign, central keratin filled cyst; often spontaneously regress
- Rat: Benign, encapsulated neoplasm with crateriform appearance, central pore, and keratin cysts; arising from epidermal cells in rats
- Mouse: Murine keratoacanthoma, most common spontaneous skin tumor in a laboratory setting; arising from follicle epithelium; benign, crateriform appearance, keratin filled cyst; must differentiate from squamous cell papilloma
Lab animals have two experimental types
- Type 1 - bud-shaped; arises from superficial hair follicle epithelium
- Type 2 - dome-shaped; arises from the deeper hair follicle or germinal bulb
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