JPC SYSTEMIC PATHOLOGY

INTEGUMENTARY SYSTEM

September 2022

I-N05 

 

Signalment (JPC 2005790):  Young broiler chicken 

 

HISTORY:  This 7 week old processed broiler chicken had a large circumferential cyst with an eroded/ulcerated surface.

 

HISTOPATHOLOGIC DESCRIPTION:  Feathered skin, 4 sections: Expanding the dermis, elevating the multifocally ulcerated epidermis, separating and compressing collagen fibers, is an unencapsulated, poorly demarcated, crateriform, moderately cellular neoplasm composed of epithelial cells arranged in islands, and cords on a dense fibrovascular to desmoplastic stroma. Neoplastic cells have distinct cell borders, a moderate amount of basophilic cytoplasm, a round to oval nucleus with finely stippled chromatin and 0-1 nucleolus. Anisocytosis and anisokaryosis are mild.  Mitoses average 2 per 2.37 mm². Neoplastic cells are multifocally dyskeratotic and form cysts lined by stratified squamous epithelium with central lamellations of keratin (keratin pearl). Surrounding neoplastic cells, expanding perivascular adventitia, separating and surrounding dermal collagen fibers, and infiltrating the deep panniculus, is an abundant inflammatory infiltrate composed of abundant heterophils, histiocytes, and fewer lymphocytes and plasma cells. Surrounding the neoplastic and inflammatory cells, the dermal collagen is largely replaced by activated fibroblasts (desmoplasia). There are rare hyperplastic feather follicles composed of moderately acanthotic follicular epithelium with rare intercellular edema (spongiosis) and moderate luminal orthokeratotic hyperkeratosis. Rarely, dermal lymphatics are multifocally dilated and contain aggregates of heterophils. Ulcerated regions of the epidermis are multifocally covered by moderate amounts of fibrin, hemorrhage, edema, previously described inflammatory cells (serocellular crust).

 

MORPHOLOGIC DIAGNOSIS:  Feathered skin: Keratoacanthoma, breed unspecified, chicken, avian.

 

CONDITION:  Avian keratoacanthoma

 

SYNONYMS:  Dermal squamous cell carcinoma; squamous epithelioma 

 

GENERAL DISCUSSION:

• 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

 

PATHOGENESIS:

• 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:

 

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

 

ULTRASTRUCTURAL FINDINGS:

 

DIFFERENTIAL DIAGNOSIS:

• Focal ulcerative dermatitis
• Squamous cell carcinoma (I-N04):  Affects older birds; reported in the crops of a psittacine and a game bird; more invasive

 

COMPARATIVE PATHOLOGY:

• Subungual keratoacanthoma (I-N31) or “claw bed tumor”, nail bed origin
• Adnexal tumors of follicular origin (I-N01, I-N02, I-N03): 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 (or invaginated) appearance, central pore, and keratin cysts; arising from epidermal cells in rats

 

REFERENCES:

1. Leininger JR, Bradley AE.  Integumentary system.  Suite AW, ed. Boorman’s Pathology of the Rat. 2^nd ed. San Diego, CA: Elsevier Inc.; 2018: 335-336.
2. Mauldin EA, Peters-Kennedy J.  Integumentary system.  In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. Philadelphia, PA: Elsevier Saunders; 2016: 703.    
3. Schat KA, Nair V. Neoplastic diseases. In: Swayne DE, et al. ed.  Diseases of Poultry. 13th ed. Ames, IA: Wiley-Blackwell; 2013: 617-618.
4. Schmidt RE, Reavill DR, Phalen DN.  Integument. In: Pathology of Pet and Aviary Birds. 2^nd ed. Ames, Iowa: John Wiley & Sons, Inc; 2015: 255.
5. Shivaprasad HL, Barnes HJ. Integumentary system. In: Abdul-Aziz T, Fletcher OJ, Barnes HJ, eds. Avian Histopathology. 4^th ed. Jacksonville, FL: American Association of Avian Pathologists; 2016: 624,639. 
6. Walling MA, Haschek WM, Rousseaux CG, Bolden B, Mahler BW. Fundamentals of Toxicologic Pathology. 3rd ed. Cambridge, MA: Elsevier; 2018: 809-810.  
7. Welle MM, Linder KE. The integument.  In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed., St. Louis, MO; Elsevier; 2022: 1122.

 

 

 

 

 

 

 

 

 

 

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