Porth's Essentials of Pathophysiology, 4e

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Disorders of Skin Integrity and Function

C h a p t e r 4 6

Nevi Almost all adults have nevi, some in greater numbers than others. Nevi can be pigmented or nonpigmented, flat or elevated, and hairy or nonhairy. Melanocytic nevi are pigmented skin lesions result- ing from proliferation of melanocytes in the epidermis or dermis. 58 Melanocytic nevi are tan to deep brown, uniformly pigmented, small papules with well-defined, rounded borders (Fig. 46-20A). They are formed ini- tially by melanocytes with their long dendritic exten- sions that are normally interspersed among the basal keratinocytes (see Chapter 45, Fig. 45-3). The mela- nocytes are transformed into round or oval melanin- containing cells that grow in nests or clusters along the dermal–epidermal junction. Because of their location, these lesions are called junctional nevi (see Fig. 46-20B). Most junctional nevi eventually grow into the surround- ing dermis as nests or cords of cells. Compound nevi contain epidermal and dermal components. In older lesions, the epidermal nests may disappear entirely, leav- ing dermal nevi . Compound and dermal nevi usually are more elevated than junctional nevi. Another form of nevus, the dysplastic nevus, is impor- tant because of its capacity to transform into malignant melanoma. 59,60 Dysplastic nevi are usually larger than other nevi (often >5 mm in diameter). Their appearance is a flat, slightly raised plaque with a pebbly surface, or a targetlike lesion with a darker, raised center and irregu- lar border (Fig. 46-21). They vary in shade from brown and red to flesh tones. A person may have hundreds of these lesions. Although dysplastic nevi can give rise to melanoma, the vast majority are stable and never prog- ress, suggesting that they are best viewed as markers for melanoma risk. Dysplastic nevi have been documented in multiple members of families prone to development of malignant melanoma. Because of the possibility of malignant transforma- tion, any mole that undergoes a change warrants imme- diate medical attention. Observe and report changes in size, thickness, or color; itching; and bleeding.

they are taken in combination with sun exposure. Sunscreens are protective agents that work by either reflecting sunlight or preventing its absorption. ■■ Thermal injury can damage the skin and subcutaneous tissues, destroying the barrier function of the skin. The extent of injury is determined by the thickness of the burn and the total body surface area involved. Treatment methods vary with the severity of injury and include immediate resuscitation and maintenance of physiologic function, wound cleaning and débridement, application of antimicrobial agents and dressings, and skin grafting. ■■ Pressure ulcers are ischemic lesions of the skin and underlying structures caused by unrelieved pressure that impairs the flow of blood and lymph. Pressure ulcers are divided into four stages, according to the depth of tissue involvement.The prevention of pressure ulcers is preferable to their treatment.The goals of prevention should include identifying at-risk persons along with the specific factors placing them at risk, maintaining and improving tissue tolerance to pressure to prevent injury, and protecting against the adverse effects of external mechanical forces (i.e., pressure, friction, and shear).

Nevi and Skin Cancers Nevi, or moles, are common congenital or acquired tumors of the skin that are benign. However, some nevi can become malignant.

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FIGURE 46-20. (A) Normal mole, with no different shades of brown, black, or tan. (From National Cancer Institute Visuals. No. AV-8809-4032. Courtesy of Skin Cancer Foundation.) (B) Junctional melanocytic nevi.These small, flat lesions are uniform in color. (From Goodheart HP. Goodheart’s Photoguide to Common Skin Disorders. Philadelphia, PA: Wolters Kluwer Health | Lippincott Williams &Wilkins; 2009:364.)