I-N20 (NP)

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 a non-encapsulated, well-demarcated, 4 x 8 mm mass composed of densely packed, randomly arranged streams and bundles of plump spindle cells that often 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, and 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. The larger, centrally located 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 and pigmented with moderate orthokeratotic hyperkeratosis. Lymphatics of the superficial dermis are occasionally ectatic, and dermal collagen bundles are separated by mildly increased clear space (edema).

MORPHOLOGIC DIAGNOSIS: Haired skin, scrotum (per contributor): Vascular hamartoma, breed unspecified, canine.

GENERAL DISCUSSION:

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, and Labrador retrievers)
Complete surgical excision is curative

PATHOGENESIS:

Congenital or developmental anomaly, often not detected until later in life
A hamartoma is the result of aberrant differentiation rather than true neoplasia
Can grow independently of growth of the animal, but often cease to grow after the animal reaches maturity

TYPICAL CLINICAL FINDINGS:

Thickened, occasionally ulcerated scrotal plaque
Slow growing, hyperpigmented macules or plaques on the scrotum, usually progress and enlarge with time
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 the overlying epidermis is typical
Ulceration, hemorrhage, and secondary inflammation are frequently present

DIFFERENTIAL DIAGNOSIS:

Hemangioma (I-N19A): Non-encapsulated, 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 (I-N19B): Invasive; pleomorphic spindle cells forming cleft-like, blood-filled vascular channels; mitotic rate varies greatly
Lymphangiosarcoma: Similar to hemangiosarcoma, but lacks blood, very aggressive, widespread and rapid metastasis

COMPARATIVE PATHOLOGY:

Horses: Vascular hamartoma – reported in ovary and tendon sheath
Cattle:
- Vascular hamartoma – reported in ovary, gingiva, testis, liver and heart
- Bovine cutaneous angiomatosis—young dairy and beef cattle; dorsum of the back; grossly red-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
Pathologic vascular overgrowths occur in the brain, spinal cord, and meninges of many animals from birth until old age

REFERENCES:

Foster RA, Premanandan C. Female Reproductive System and Mammae. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022: 1276.
Gross TL, Ihrke PJ, Walder EJ, Affolter VK. Mesenchymal neoplasm and other tumors. In: Skin Diseases of the Dog and Cat Clinical and Histopathologic Diagnosis. 2nd ed., Ames, IA: Blackwell Science Ltd.; 2005:738-739.
Marr J, Miranda IC, Miller AD, Summers BA. A Review of Proliferative Vascular Disorders of the Central Nervous System of Animals. Vet Pathol. 2021 Sep;58(5):864-880.
Mauldin EA, Peters-Kennedy J. Integumentary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. New York, NY: Elsevier Limited; 2015:703,705.
Hendrick MJ. Mesenchymal Tumors of the Skin and Soft Tissues. In: Meuten DJ, ed. Tumors in Domestic Animals. 5th ed. Ames, IA: John Wiley & Sons, Inc; 2017:166.
Miller WH, Griffin CE, Campbell KL. Muller and Kirk's Small Animal Dermatology. 7th ed., Philadelphia, PA: WB Saunders Company; 2012:828.
Robinson, WF, Robinson NA. Cardiovascular system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. New York, NY: Elsevier Limited; 2015:99.