C h a p t e r 4 6
Disorders of Skin Integrity and Function
1173
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.
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.
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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).
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.)
A
B
