JPC SYSTEMIC PATHOLOGY
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.
SYNONYMS: Fibroepithelial polyp, fibrovascular papilloma, skin tag, skin polyp
· Pedunculated to elongated proliferation of epidermis and dermal collagen
· Large and giant breeds may be predisposed, especially the Doberman pinscher and Labrador retriever
· Cause unknown
· May be a proliferative response to trauma or focal 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
· Few or no adnexa
· Mild mononuclear inflammation may be present
· 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
· Nodular dermatofibrosis: Multiple fibromatous nodules (collagenous hamartomas) in German shepherd dogs (occasionally other breeds) associated with renal cystadenocarcinoma and uterine leiomyoma; poorly demarcated proliferation of dermal collagen with epithelial hyperplasia and variable inflammation
· Collagen nevus (hamartoma): Poorly demarcated, exophytic proliferation of mature, haphazardly arranged collagen that may contain atrophied, entrapped adnexa
· Fibroadnexal dysplasia: Proliferation of mature dermal collagen, epidermal hyperplasia and disorderly proliferation of dysplastic adnexa
· Squamous papilloma: Epidermal proliferation with scant, delicate supporting fibrous tissue
· Fibropapilloma: Marked epidermal proliferation with broad, interlacing rete pegs +/- viral cytopathic effect in epithelium
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.