Small Animal Dermatology, 3rd edition

496 DISEASES/DISORDERS

 Approximately 50% located on the trunk and perineum; 40% on extremities; 10%

on the head and neck region; breed predilection for locations reported (especially

hindlimb) (Figures 33.9, 33.10).

 Poorer prognosis associated with tumors on the perineum, prepuce, scrotum, groin,

axillae, and digits (Figures 33.11–33.13).

 Regional lymphadenopathy: may develop when a high-grade tumor metastasizes to

draining lymph nodes.

 Hepatomegaly and splenomegaly: features of disseminated mast cell neoplasia.

Cats

 Cutaneous: primarily found in the subcutaneous tissue or dermis; may be papular

or nodular, solitary or multiple, and haired or alopecic or have an ulcerated surface;

slight predilection for the head and neck regions (Figures 33.14, 33.15).

 Clusters of nodules that appear on the face and ears may regress spontaneously (his-

tiocytic form especially in young Siamese) (Figure 33.16).

 Most feline tumors are well differentiated and benign.

 Urticaria pigmentosa appears as hyperpigmented and/or erythematous macules

around the mouth, chin, neck, and eyes (spontaneous regression in some cases) (Fig-

ure 33.17).

 Intestinal mast cell tumor: firm, segmental thickenings of the small intestinal wall;

measures 1–7 cm in diameter; metastases to the mesenteric lymph nodes, spleen, liver,

and (rarely) lungs (Figure 33.18).

DIFFERENTIAL DIAGNOSIS

 Any other skin or subcutaneous tumor, benign or malignant, including lipoma.

 Insect bite or allergic reaction.

DIAGNOSTICS

 Cytologic examination of fine-needle aspirate:
Most important preliminary diagnostic test
Round cells with basophilic cytoplasmic granules that do not form sheets or

clumps (Figure 33.19)

Malignant mast cells may be agranular; occurrence of a large eosinophilic infil-

trate may suggest mast cell tumor

Granules may not stain well with Diff-Quick stain; may require methanol fixative

for at least 2 minutes prior to routine staining

Cytology not useful to determine grade or prognosis.

 Use of buffy coat cytology and liver/spleen fine-needle aspirate is controversial and

often not considered important in staging of disease.

 Tissue biopsy: necessary for definitive diagnosis and grading.