Small Animal Dermatology, 3rd edition

678 DISEASES/DISORDERS

keratin) in well-differentiated tumors, desmosomes and mitotic figures common;

Bowen’s disease– dysplastic, highly ordered keratinocytes proliferate, replacing nor-

mal epidermis, but do not penetrate the basement membrane into the surrounding

dermis (in situ):solar induced– trabeculae of squamous cells invade into the dermis;

neoplastic cell aggregates; keratin pearls; keratinocyte cellular and nuclear pleomor-

phism; mitotic activity higher in dogs than cats; associated with dermal solar elastosis

and fibrosis.

 Melanocytic tumors: neoplastic melanocytes that may be spindle, epithelial, or round

in appearance with variable degrees of pigmentation; cells arranged in clusters, cords,

or whorls; infiltration of pigment-laden macrophages; variable mitotic figures and

pleomorphism related to the degree of malignancy; mitotic index most reliable way to

predict tumor behavior; 10% of histologically benign tumors may behave in a malig-

nant manner.

 Basal cell tumor: nonencapsulated dermal to subcutaneous mass composed of cords

or nests of neoplastic basal cells; may be pigmented or cystic; central areas of squa-

mous differentiation; nuclear hyperchromasia; frequent mitotic figures.

 Sebaceous gland tumors:
Hyperplasia: multiple enlarged mature sebaceous lobules with single peripheral

layer of basaloid epithelial cells clustered around dilated sebaceous ducts; no

mitotic activity

Sebaceous adenoma: mature sebaceous lobules with increased numbers of basa-

loid epithelial cells; sebaceous ducts not prominent; cystic degeneration; low

mitotic activity

Epithelioma: irregular islands and lobules of basaloid epithelial cells with reac-

tive collagen; higher mitotic activity

Adenocarcinoma: poorly defined lobules of large epithelial cells with varying

degrees of differentiation; high mitotic activity.

 Hair follicle tumors:
Trichoepithelioma: germinal hair follicle cells differentiate toward hair follicles

and shaft structures

Pilomatrixoma: germinal cells tend to differentiate toward hair bulb/matrix

Trichoblastoma: germinal cells differentiate toward hair bulb

Trichofolliculoma: may actually be a follicular or pilosebaceous hamartoma

rather than a true neoplasm

Dilated pore of Winer: benign hair follicle tumor or cyst.

THERAPEUTICS

 Invasive tumors: inpatient; require aggressive surgical excision or radiotherapy.

 Superficial tumors: surgery, cryosurgery, photodynamic therapy, or irradiation.

 Plesiotherapy (topical radiation, strontium-90).

 Photodynamic therapy.

 Topical synthetic retinoids or imiquimod: early superficial lesions.

 Wide surgical excision.