Page 50 - The Netter Collection of Medical Illustrations - Integumentary System_ Volume 4 ( PDFDrive )

Plate 2-23 Integumentary System

COMMON ACQUIRED NEVI AND GIANT CONGENITAL MELANOCYTIC NEVI

MELANOCYTIC NEVI
(Continued)

testicular tumors, pituitary tumors, psammomatous
melanotic schwannomas, and adrenal tumors. This is a
rare syndrome that has been determined to be caused
by a genetic defect in the gene PRKAR1A. This is a
tumor suppressor gene that encodes a protein kinase A
subunit.
Congenital melanocytic nevi can be divided clinically
into distinct subtypes based on size (small, medium, and
giant). Small congenital nevi are the most common
type; they are defined as those nevi smaller than 2 cm
in greatest diameter. These nevi occur with equal fre-
quency in males and females and have no race predilec-
tion. Some authors estimate their prevalence at about
1% of the population. These nevi are typically described
as well-defined macules, papules, or plaques. They are
hyperpigmented compared with the normal surround-
ing skin. They are almost always uniform in color and
symmetric. Over time, some 50% develop terminal hair Common acquired nevus Atypical/dysplastic nevus with
growth within the nevi. The risk of malignant trans- surrounding solar lentigines
formation in these small congenital nevi is low and
approaches that of the common acquired melanocytic
nevi. Melanoma can arise in these nevi at any point in
the patient’s life but usually after puberty.
Medium-sized congenital melanocytic nevi are
defined as those that have a diameter between 2 and
20 cm. They have the same risk of malignant transfor-
mation as small congenital nevi. They occur equally in
males and females and can be seen in about 1% of the
population. They can occur anywhere on the body.
Giant or large congenital melanocytic nevi, also
known as “bathing trunk” nevi, are important clinically
in many ways. First, they have an increased risk of
malignant transformation. This transformation can be
difficult to discern clinically until the lesions are quite
large. Most melanomas develop in a dermal or subcu-
taneous location, which make them difficult to assess
clinically. Melanomas typically occur before puberty,
and they have been reported to occur in as many as 15%
of giant congenital nevi. The risk of malignant trans-
formation is higher in axial nevi than in acral nevi. For
this reason, these lesions are treated more aggressively,
and patients with large congenital melanocytic nevi
need lifelong, frequent routine follow-up. These nevi
occur equally in men and women and in any racial
group. They affect the truncal region more often than
any other region of the body. Nevus spilus Halo nevus
The significant finding of neurocutaneous melanosis
occurs at a higher rate in patients with large congenital
nevi of the trunk. These nevi almost always occur over
the majority of the trunk, and they can have any number
of satellite melanocytic nevi. Patients with large truncal
congenital melanocytic nevi should undergo magnetic
resonance imaging (MRI) of the nervous system to
evaluate for neurocutaneous melanosis. Patients with
neurocutaneous melanosis are at a high risk (almost
50%) for development of leptomeningeal melanoma,
which is almost always fatal. A multidisciplinary normal melanocytes found within the stratum basalis. histologically. Based on the location of the melanocyte
approach to care for these patients is required, includ- They are round and uniform in shape and show increas- nests, they can be classified as junctional, intraepider-
ing the patient’s pediatrician, dermatologist, neurolo- ing maturation with depth in the dermis. Maturation of mal, dermal, or compound nevi. A junctional nevus has
gist, and neurosurgeon. nevi cells implies a decrease in the ratio of nuclear to its nests arranged along the basement membrane
Histology: In common acquired melanocytic nevi, cytoplasmic volume and an overall decrease in the size zone, whereas a compound nevus has epidermal and
the melanocytes are arranged symmetrically in a lateral of the melanocytes. The melanocytes are still uniform dermal nests.
fashion. They are arranged in nests. The nested mela- in size and shape at various depths within the dermis; Blue nevi are located entirely within the dermis.
nocytes do not have the typical dendritic appearance of they are not symmetric vertically. Many forms are seen These nevi are made of melanocytes that resemble

36 THE NETTER COLLECTION OF MEDICAL ILLUSTRATIONS