JPC SYSTEMIC PATHOLOGY
Signalment (JPC#1718684): Age and breed unspecified dog.
HISTORY: Dog presented with a reddened plaque-like growth involving the skin of the scrotum.
HISTOPATHOLOGIC DESCRIPTION: Haired skin, scrotum: Expanding the dermis is an unencapsulated, well-demarcated, 4 x 8 mm mass composed of densely packed, randomly arranged streams and bundles of plump spindle cells that form well-differentiated, variably sized, blood filled, vascular channels lined by endothelium and surrounded by smooth muscle and collagen bundles. The spindle cells have variably distinct borders, moderate amounts of finely fibrillar, pale eosinophilic cytoplasm, elongate nuclei with finely stippled chromatin, and a single magenta nucleolus. Mitotic figures are not observed. Blood vessels within the mass are lined by endothelium with rounded nuclei, and larger centrally oriented vessels are often filled with erythrocytes, abundant fibrin, and aggregates of neutrophils. Multifocally, there are predominately perivascular aggregates of degenerative neutrophils. The epidermis is mildly hyperplastic, pigmented, and contains moderate amounts of orthokeratotic hyperkeratosis with a loss of adjacent adnexal structures. Occasionally lymphatics of the superficial dermis are ectatic and collagen bundles are separated by clear space (edema).
MORPHOLOGIC DIAGNOSIS: Haired skin, scrotum (per contributor): Vascular hamartoma, breed unspecified, canine.
- Hamartoma: A benign, disordered overgrowth of mature tissue elements indigenous to the organ in which they arise with loss of normal architecture of surrounding tissues
- A vascular hamartoma contains structurally normal vessels with all supporting elements (as opposed to a proliferation of endothelial cells, e.g. hemangioma)
- Vascular hamartomas most common in the scrotum of middle-aged dogs with pigmented skin (Scottish terriers, Airedales, Kerry blue terriers, Labrador retrievers); usually progress and enlarge with time
- Complete surgical excision is curative
- Congenital or developmental anomaly, often not detected until later in life
- Result of aberrant differentiation rather than true neoplasia
- Can grow independently of growth of the animal, but often cease to grow after animal reaches maturity
TYPICAL CLINICAL FINDINGS:
- Thickened, occasionally ulcerated scrotal plaque
- Slow growing, hyperpigmented macules or plaques on the scrotum
- May hemorrhage periodically
TYPICAL GROSS FINDINGS:
- Solitary or multiple, flat or firm, pigmented plaque strictly limited to the skin of the scrotum
- Ulceration and hemorrhage due to irritation, licking, and secondary inflammation or bacterial infection
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Multiple clusters or lobules of redundant vascular structures within the dermis that surround pre-existing blood vessels and are poorly circumscribed
- Redundant vascular structures are lined by endothelial cells with plump or rounded, dark, uniform nuclei
- Hyperplastic vessels within the center are frequently enlarged and dilated (telangiectasia); vessels towards the periphery consist of capillary buds with barely discernible lumina
- Mitotic figures are very rare; mitotic atypia is not present.
- Proliferation of spindle cells (fibroblasts or pericytes) may accompany blood vessels
- Fibrosis may be observed
- Acanthosis and hyperpigmentation of overlying epidermis is typical
- Ulceration, hemorrhage and secondary inflammation frequently present
- Hemangioma: Unencapsulated, deep dermis, proliferation of endothelial cells that form channels unaccompanied by muscle or pericytes that support normal vessels
- Angiokeratoma: Hemangioma of the immediately subepithelial dermis or subconjunctival lamina propria, with marked epithelial hyperplasia
- Lymphangioma: Similar to hemangioma, but lacks blood
- Hemangiosarcoma: Invasive, pleomorphic spindle cells forming cleft-like channels, mitotic rate varies greatly
- Lymphangiosarcoma: Similar to hemangiosarcoma, but lacks blood, very aggressive, widespread and rapid metastasis
- Horses: Vascular hamartoma – reported in ovary and tendon sheath
- Foal: Vascular hamartoma – reported in central nervous system
- Cattle: Vascular hamartoma – reported in ovary, gingiva, testis, liver and heart Bovine cutaneous angiomatosis—young dairy and beef cattle; dorsum of the back; grossly reddish gray to pink, soft, sessile or pedunculated 0.5 to 2.5 cm diameter masses; site of recurring hemorrhage
- Swine: Vascular hamartoma – reported in ovary; vascular hamartoma or hemangioma of the scrotum – Yorkshires and Berkshires; grossly small multiple papillomatous growths that resemble hematomas
- Rat: Vascular hamartoma – reported in the uterus
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