Page 51 - The Netter Collection of Medical Illustrations - Integumentary System_ Volume 4 ( PDFDrive )

Plate 2-24 Benign Growths

CONGENITAL NEVI

Small
MELANOCYTIC NEVI congenital
(Continued) Medium nevus
congenital
nevus
dendrites. The dendritic processes contain melanin
pigment, and this pigment is responsible for the color-
ation of the lesion. Collagen is interwoven between
the dermally located melanocytes. Melanophages are
almost always seen in and around the lesion. A grenz
zone is sometimes appreciated above the melanocytic
lesion. Numerous histological subtypes of blue nevi
have been described, including the dendritic blue nevus
(common blue nevus), amelanotic blue nevus, cellular
blue nevus, and epithelioid blue nevus.
Small, medium, and large congenital nevi all show
the same histological characteristics, and they cannot
be distinguished on pathological evaluation. The major
criteria used to separate congenital nevi from other
types of nevi are size and location. The nests are found
deep within the dermis and can also be found within
the subcutaneous tissue, fascia, and underlying muscle.
Infiltration of muscle is unusual and is more likely to
be seen in large congenital nevi. The nests of nevus cells
accumulate around adnexal structures and are fre-
quently seen juxtaposed to hair follicles, sebaceous
glands, and eccrine glands. The melanocytes can pen-
etrate the arrector pili muscles. The nevus cells show
proper maturation and are uniform in appearance.
Pathogenesis: There are many conflicting theories as
to the pathogenesis of common acquired melanocytic
nevi and blue nevi. Some think that there is an abnor-
mal migration of melanocytes embryologically, whereas
others believe that stem cells are located within the Congenital nevus low
dermis or epidermis and melanocytes migrate upward power. Nests of melano-
or downward to form the nevi. Perhaps a combination cytes are seen throughout
of these processes occurs, but no definitive pathogenic the dermis. They extend
mechanism has been universally accepted. deep into the dermis and
Congenital melanocytic nevi are thought to be caused subcutaneous tissue around
by an embryological malfunction of melanocyte migra- adnexal structures.
tion. The precise mechanism that causes the disrupted
or abnormal migration of melanocytes into the involved
areas has not been determined. Migration in these cases
is believed to be controlled by a complex but abnormal
growth and regulatory signaling pathway.
Treatment: Common acquired melanocytic nevi do Giant congenital bathing trunk nevus
not need to be treated. They can be removed by various
means for cosmetic purposes. Shave removal and punch
biopsy removal are two highly successful techniques.
Elliptical excision should be reserved for larger lesions Congenital nevus high power.
in areas where the scar can be camouflaged. Only highly Melanocytes are seen adjacent
skilled physicians should consider removing pigmented to adnexal structures. This is
lesions with laser therapy, because there is no tissue left one characteristic finding in
for histological evaluation. congenital nevi.
Blue nevi are easily removed by punch biopsy or
elliptical excision. They are often removed for cosmetic
reasons, and a small excision gives an excellent cosmetic
result. patients should be referred to a plastic surgeon for goal should be 100% removal, although in some cases
Removal of small and medium congenital nevi should evaluation. The social and psychological well-being of this is not feasible. If the nevi cover 10% to 30% or
be done with surgical excision. This removes the entire the child can be enhanced by having a disfiguring con- more of body surface area, they become almost impos-
lesion and allows for pathological evaluation. Most of genital nevus removed. sible to remove. In these cases, as in all the others, the
these small and medium congenital melanocytic nevi Large congenital nevi present the biggest treatment importance of lifelong surveillance needs to be taught
can be observed over time and removed if there are difficulty because of the high rate of malignant trans- to the parents, the afflicted individuals, and the partici-
changes. Serial photographs are invaluable in monitor- formation. If possible, serial excisions to remove large pating physicians. The goal in these cases is to biopsy
ing these nevi for changes. Some of these lesions occur nevi are the best option. Tissue expanders are often and remove any changing areas of the nevi in an effort
in cosmetically sensitive areas, such as the face, and used to help decrease the need for skin grafting. The to prevent metastasis if a melanoma were to develop.

THE NETTER COLLECTION OF MEDICAL ILLUSTRATIONS 37