Small Animal Dermatology, 3rd edition

576 DISEASES/DISORDERS

Individual plaques and nodules (often with actinic comedones) coalesce to form

larger lesions

Affected areas become extensive; inflammation and exudation develop with sec-

ondary furunculosis

Axillae, ventral abdomen, and medial thigh primary sites; less often dorsal muz-

zle and eyelid margin

Cats: preauricular regions, as well as pinnal margins, nasal planum, and eyelid

margins; lesions often traumatized, resulting in scabbing and crusting.

 Solar-induced hemangioma (HA) and hemangiosarcoma (HAS) (Figures 39.9–39.12):
UVL-induced HA and HSA are superficial and dermal in location; behavior dif-

fers from non-UVL-induced tumors

HA is more common than HSA

Early lesions may appear as erythematous or purpuric plaques (mimicking

telangiectasia); vasoproliferative plaque

Lesions may be discrete and well demarcated or poorly circumscribed, reddened,

or dark-appearing nodules to masses

Often multiple

UVL-induced HA and HSA often associated with other forms of photodermatosis

HA: behaviorally benign

HSA: metastasis in fewer than 20% of superficial (solar-induced) cases.

 Squamous cell carcinoma (SCC) (Figures 39.13–39.18):
80% of cases arise in association with AK
SCC may also develop secondary to chronic inflammation or viral infection
Most common cutaneous malignant neoplasm in cats (15–49%); second most

common in dogs (3–20%)

Single or multiple

Initial lesions: shallow, crusted ulcerations with peripheral alopecia and ery-

thema

Intermediate lesions: eroded and exudative plaques; scabbed surface

Late lesions: deep, crateriform and indurated patches or plaques

Cutaneous horns (rare)

Cats: external nares may be proliferative and scabbed or ulcerative; pinnal lesions

often traumatized

Locally highly invasive and destructive with significant tissue loss; neoplastic

tissue may extend beyond visible boundaries

Hemorrhage may be severe from erosion through local blood vessels

Metastasis is rare

Secondary bacterial infection results in pain and systemic symptoms.

DIFFERENTIAL DIAGNOSIS

 Solar dermatitis: lupus erythematosus (discoid, cutaneous, systemic), pemphigus

erythematosus, dermatomyositis, vasculitis, thermal burn, neoplasia, and bacterial

folliculitis.