Small Animal Dermatology, 3rd edition

CHAPTER 2 LESION DESCRIPTION/TERMINOLOGY 13

Follicular cast: accumulation of keratinaceous or sebaceous material above the

level of the follicular ostia; may be adherent to hair shaft (Figure 2.3)

Milia: keratin filled cyst within the epidermis (Figure 2.4)

Comedo: dilated hair follicle blocked by sebaceous and epidermal debris; when

the follicular ostia is open to the air, debris will darken to form a “blackhead”

(Figure 2.5)

Lesions under 1 cm in diameter:

Macule: nonpalpable change in skin color; increased or decreased pigmen-

tation, hemorrhage (nonblanching), or erythema (Figure 2.6)

Papule: solid elevation of the skin (Figure 2.7)

Vesicle: acellular fluid-filled lesion, within or just below the epidermis

(Figure 2.8)

Pustule: cellular fluid-filled lesion, within or just below the epidermis;

fluid most often contains neutrophils, but may also contain eosinophils

(Figure 2.9)

Nodule: solid elevation of the skin that extends into deeper layers

(Figure 2.10)

Lesions over 1 cm in diameter:

Patch: nonpalpable change in skin color; large macule (Figure 2.11)

Plaque: flat, palpable and solid elevation; large or coalescing papules

(Figure 2.12)

Wheal: temporary accumulation of fluid in the dermis; often creates a

sharply demarcated (steep-walled) raised area; flattens with digital pressure

(Figure 2.13)

Bulla: large accumulation of fluid, often extending into the dermis

(Figure 2.14)

Abscess: very large accumulation of cellular fluid that extends deep into the

dermis and subcutaneous tissues

Cyst: epithelium-lined cavity with fluid or semi-solid matter, often just

beneath the epidermis (Figure 2.15)

Tumor: large mass that may involve the skin and deeper tissues

(Figure 2.16)

Pigmentation change:

Hyperpigmentation: increase in cutaneous pigmentation

Hypopigmentation: decrease in cutaneous pigmentation

Leukoderma: white skin (Figure 2.17)

Leukotrichia: white hair (Figure 2.18).

 Secondary lesions develop from primary lesions, most often induced by the patient

or by the environment:

Epidermal collarette: circular accumulation of scale, resulting from the enlarge-

ment of a ruptured vesicle or pustule (Figure 2.19)

Excoriation: linear erosion with erythema and crusting as a result of self-trauma

(Figure 2.20)

Lichenification: thickening of the skin with accentuation of the normal skin pat-

tern caused by chronic inflammation and self-trauma (Figure 2.21)