What are Nevi, or Moles, part three

SPECIAL FORMS
Special forms of pigmented lesions include congenital nevus, halo nevus, nevus spilus, Becker's nevus, benign juvenile melanoma (Spitz nevus), blue nevus, and labial melanotic macules.
Congenital nevi.
Congenital nevi (birthmarks) are present at birth and vary in size from a few millimeters to several centimeters, covering wide areas of the trunk, an extremity, or the face. Not all pigmented lesions present at birth are congenital nevi; cafe-au-lait spots may also be present at birth. The largest lesions are referred to as giant hairy nevi. Giant congenital nevi on the trunk are referred to as bathing trunk nevi .
Congenital nevi may contain hair; if present, it is usually coarse. Such nevi are uniformly pigmented, with various shades of brown or black predominating , but red or pink may be a minor or sometimes predominant color . Most are flat at birth, but become thicker during childhood, and the surface becomes verrucous and sometimes nodular.
The risk of developing melanoma in very large lesions is significant. Malignant transformation may occur early in childhood; therefore, large, thick lesions should be removed as soon as possible. The risk of developing malignancy may be related to the number of melanocytes and consequently to the size and thickness; however, melanomas have also developed in small congenital nevi. There is a large risk of melanoma in patients with nevi covering more than 5% of the body surface area. The risk of malignant degeneration for smaller congenital nevi is unknown. A report showed histologic features of congenital nevi in 8.1% of the melanoma specimens studied.
Management.
The incidence of melanomas in small congenital nevi is unknown. Persons with large congenital nevi (bathing trunk nevi) are at definite risk for the development of melanoma in childhood, and these nevi are managed by a plastic surgeon. Because of the possibility of malignant degeneration of congenital nevi, some experts recommend that all congenital nevi be considered for prophylactic excision. All congenital moles should be checked by a dermatologist. If a congenital mole is not surgically removed, it should be examined on a regular basis.
Nevus spilus.
Nevus spilus is a hairless, oval or irregularly shaped, brown lesion that is dotted with darker brown-to-black spots. The brown area is usually flat, and the black dots may be slightly elevated and contain typical nevus cells . There is considerable variation in size, ranging from 1 to 20 cm; they may appear at any age. The anatomic position or time of onset is not related to sun exposure.
Nevus spilus is flat and necessitates excision and closure if the patient desires removal.
Becker's nevus.
Becker's nevus is not a nevocellular nevus because it lacks nevus cells. The lesion is a developmental anomaly consisting of either a brown macule , a patch of hair, or both . Nonhairy lesions may later develop hair. The lesions appear in adolescent men on the shoulder, submammary area, and upper and lower back. Becker's nevus varies in size and may enlarge to cover the entire upper arm or shoulder. The border is irregular and sharply demarcated. Malignancy has never been reported.
Becker's nevus is usually too large to remove and is best left untouched. The hair may be shaved or permanently removed.
Halo nevi.
A compound or dermal nevus that develops a white border is called a halo nevus. The depigmented halo is symmetric and round or oval with a sharply demarcated border . There are no melanocytes in the halo area. Histologically, chronic inflammatory cells may be present. Most halo nevi are located on the trunk; they never occur on palms and soles. Halo nevi develop spontaneously, most commonly during adolescence. They may occur as an isolated phenomenon or several nevi may spontaneously develop halos. Halos may repigment with time or the nevus may disappear. Repigmentation does not follow removal of the nevus. The incidence of vitiligo may be increased in patients with halo nevi. A halo may rarely develop around malignant melanoma, but in such instances it is usually not symmetric.
Removal of a halo nevus is unnecessary unless the nevus has atypical features. Parental concern over this impressive change is often reason for a conservative excision. In such cases, the mole part of a halo nevus may be removed by shave or excision.
Spitz nevus.
Spitz nevus, or benign juvenile melanoma, is most common in children, but does appear in adults. The term melanoma is used because the clinical and histologic appearance is similar to melanoma. They are hairless, red or reddish-brown, dome-shaped papules or nodules with a smooth or warty surface; they vary in size from 0.3 to 1.5 cm. The color is caused by increased vascularity, and bleeding sometimes follows trauma. Spitz nevi are usually solitary but may be multiple. They appear suddenly and, contrary to slowly evolving common moles, patients can sometimes date their onset. The benign juvenile melanoma should be removed for microscopic examination. Histologic differentiation from melanoma is sometimes difficult.
Blue nevus.
The blue nevus is a slightly elevated, round, regular nevus, usually less than 0.5 cm, and contains large amounts of pigment located in the dermis . The brown pigment absorbs the longer wavelengths of light and scatters blue light (Tyndall effect). The blue nevus appears in childhood and is most common on the extremities and dorsum of the hands. A rare variant, the cellular blue nevus, is larger (usually greater than 1 cm) and nodular and is frequently located on the buttock. There are reported cases of malignant degeneration of these larger blue nevi into melanomas.
Labial melanotic macule.
Brown macules on the lower lip are relatively common, especially in young adult women. Histologically, they resemble freckles and not lentigo, but unlike freckles, they do not darken with sun exposure.