JPC SYSTEMIC PATHOLOGY

INTEGUMENTARY SYSTEM

October 2022

I-N28 (NP)

 

Signalment (JPC# 2233443): Age and breed unspecified dog

 

HISTORY:  A slow growing neoplasm removed from the 2nd digit of the left forepaw

 

HISTOPATHOLOGIC DESCRIPTION:  Haired skin, 2nd digit, left paw (per contributor): Expanding the dermis, elevating the mildly hyperplastic epidermis, and surrounding few dysplastic and haphazardly arranged hair follicles and adnexa is a well vascularized, pedunculated, 2.5 x 1 cm mass composed of thick, tightly packed collagen bundles admixed with loosely arranged collagen and moderate numbers of reactive fibroblasts.  Near the tip of the mass, collagen bundles are separated by clear space and lymphatics are ectatic (edema). Within the neck of the mass, there are few scattered perivascular lymphocytes, plasma cells, macrophages, and neutrophils. There is diffuse, mild, orthokeratotic hyperkeratosis, acanthosis, spongiosis, intracellular edema, and short, rarely anastamosing rete ridges. Multifocally within the subjacent dermis, hair follicles and adnexa are surrounded by occasional lymphocytes, plasma cells, and macrophages.  

 

MORPHOLOGIC DIAGNOSIS:  Haired skin, 2nd digit, left forepaw (per contributor):  Acrochordon, breed not specified, canine.

 

CONDITION:  Acrochordon

 

SYNONYMS:  Fibroepithelial polyp, fibrovascular papilloma, skin tag, skin polyp

 

GENERAL DISCUSSION:

• Pedunculated to elongated proliferation of epidermis and dermal collagen
• Large and giant breeds may be predisposed, especially the Doberman pinscher and Labrador retriever

 

PATHOGENESIS:

• Cause unknown
• May be proliferative response to inflammation (e.g. trauma or furunculosis)

 

TYPICAL CLINICAL FINDINGS:

• Common sites include the trunk, sternum, and over bony prominences
• Middle-aged to old dogs
• Excision is curative

 

TYPICAL GROSS FINDINGS:

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Dermis expanded by normal but redundant, tightly packed collagen bundles
• Epidermis is moderately acanthotic, hyperkeratotic, and/or hyperpigmented
• Well-vascularized
• Few or no adnexa
• Mild mononuclear inflammation may be present

 

DIFFERENTIAL DIAGNOSIS:  

• Fibroma (I-N15A):  Well-circumscribed nodule composed of whorls and interlacing bundles of collagen and fibroblasts that compress adjacent tissue; lacks inflammation and vascular proliferation
• Collagen nevus (hamartoma):  Focal, firm, dome-shaped nodules composed of excessive accumulations of dermal collagen; haphazardly arranged collagen that may contain atrophied, entrapped adnexa
• Nodular dermatofibrosis:  Multiple fibromatous nodules (collagenous hamartomas) in German shepherd dogs (occasionally other breeds) associated with internal neoplasia (renal cell adenomas and carcinomas, uterine leiomyoma, cystadenocarcinoma); poorly demarcated proliferation of dermal collagen with epithelial hyperplasia and variable inflammation 
• Fibroadnexal dysplasia:  Proliferation of mature dermal collagen, epidermal hyperplasia and disorderly proliferation of dysplastic adnexa; may contain adipocytes
• Fibropruritic nodule:  Well circumscribed raised masses on caudal dorsum that affect flea bite allergic dogs; often ulcerated and composed of collagen rich stroma in dermis
• Squamous papilloma:  Epidermal proliferation with scant, delicate supporting fibrous tissue
• Fibropapilloma:  Marked epidermal proliferation with broad, interlacing rete pegs +/- viral cytopathic effect in epithelium

 

REFERENCES:

1. Goldschmidt MH, Munday JS, Scruggs JL, Klopfleisch R, Kiupel M. Volume 1: Epithelial Tumors of the Skin. In: Kiupel M, ed. Surgical Pathology of Tumors of Domestic Animals. Washington, DC, Davis-Thompson DVM Foundation; 2019: 233-235.
2. Gross TL, Ihrke PJ, Walder EJ, Affolter VK. Fibrous tumors. In: Skin Diseases of the Dog and Cat. Ames, IA:Blackwell Publishing; 2005:713-716.
3. Mauldin EA and Peters-Kennedy J. Integumentary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. Philadelphia, Pennsylvania: Elsevier; 2016:692, 722-723.
4. Welle MW, Linder KE. The integument. In: McGavin MD, Zachary JF, eds. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:1134.

 

 

 

 

 

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