JPC SYSTEMIC PATHOLOGY
INTEGUMENTARY SYSTEM
September 2025
I-N28
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 cm x 1 cm mass composed of thick, tightly packed collagen bundles interspersed 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 base 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
- Can occur in the oral cavity; lip and gingival mucosa and the soft and hard palate (Nordio, 2023)
- Large and giant breed dogs 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:
- Solitary or multiple; pedunculated, exophytic, filiform; smooth or hyperkeratotic; soft mass(es) that may be a few centimeters in length and up to 1 cm in width
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:
- 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.
- Nordio L, Stefanello C, Gasparini S. Oral fibroepithelial polyps ("chewing granulomas") in 21 dogs: Histomorphology, immunohistochemical characterization, and clinical outcome. Vet Pathol. 2023 Mar;60(2):172-177.
- 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.
