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Type of Nevus

  1. Atypical Melanocytic Nevus
    Occur both in an autosomal dominant familial melanoma-prone setting (familial mole-melanoma syndrome, dysplastic nevus syndrome, BK mole syndrome) and as a sporadic event.10% of those with the syndrome have a melanoma develop before age 20 yr. Risk for development of melanoma is essentially 100% in individuals with dysplastic nevus syndrome. atypical mole syndrome - lesions in those individuals without an autosomal dominant familial history of melanoma but with more than 50 nevi most common on the posterior trunk. do not usually develop until puberty. prudent to excise borderline atypical nevi in immunocompromised children or in those treated with x-irradiation or chemotherapeutic agents.
  2. Congenital Melanocytic Nevus
    1. Congenital melanocytic nevi are present in approximately 1% of newborn infants. These nevi have been categorized by size: giant congenital nevi are more than 20 cm in diameter (adult size), small congenital nevi are less than 2 cm in diameter, and intermediate nevi are in between in size.
    2. Differential diagnosis includes mongolian spots, café-au-lait spots, smooth muscle hamartoma, and dermal melanocytosis (nevi of Ota and Ito).
    3. Sites of predilection of small congenital nevi are the lower trunk, upper back, shoulders, chest, and proximal limbs. The lesions may be flat, elevated, verrucous, or nodular.15% of melanomas arise within small congenital nevi.
    4. Removal of all small congenital nevi is not warranted, particularly in view of the fact that development of melanoma in a small congenital nevus is an exceedingly rare event before puberty.
      1. Giant congenital pigmented nevi occur most commonly on the posterior trunk (bathing trunk nevus) associated with leptomeningeal melanocytosis and their predisposition for development of malignant melanoma.
      2. Leptomeningeal involvement occurs most often when the nevus is located on the head or midline on the trunk, particularly when associated with “satellite” melanocytic nevi.
      3. Nevus cells within the leptomeninges and brain parenchyma may cause increased intracranial pressure, hydrocephalus, seizures, retardation, and motor deficits and may result in melanoma.  Asymptomatic leptomeningeal melanosis was noted on MRI scans of approximately one third of individuals with a giant congenital nevus.
  3. Halo Nevus (Leukoderma Acquisitum Centrifugum)
    1. Halo nevi occur primarily in children and young adults, most commonly on the back.
    2. Development of the halo may coincide with puberty or pregnancy.
    3. Several pigmented nevi frequently develop a halo simultaneously. Subsequent disappearance of the central nevus over several months is the usual outcome, and the depigmented area may or may not become repigmented.
    4. The pale halo reflects disappearance of the melanocytes. This phenomenon is associated with a. congenital nevi, b. blue nevi, c. Spitz nevi, d. dysplastic nevi, e. neurofibromas, f. primary and secondary malignant melanoma g.  poliosis, h. Vogt-Koyanagi-Harada syndrome, and pernicious anemia. i. Patients with vitiligo have an increased incidence of halo nevi.
    5. Individuals with halo nevi have circulating antibodies against the cytoplasm of malignant melanoma cells.
  4. Nevus of OTA
    1. Nevus of Ota consists of a permanent patch composed of blue, black, and brown, partially confluent macules occur unilaterally in the areas supplied by the 1st and 2nd divisions of the trigeminal nerve. Malignant change is exceedingly rare.
    2. Nevus of Ito is localized to the supraclavicular, scapular, and deltoid regions.
  5. Blue Nevi
    The common blue nevus is a solitary, asymptomatic, smooth, dome-shaped, blue to blue-gray papule.Blue nevus is nearly always acquired, often during childhood and more commonly in females, characterized by groups of intensely pigmented spindle-shaped melanocytes in the dermis.
  6. This Nevus is Benign.
    1. The cellular blue nevus is typically 1–3 cm in diameter and occurs most frequently on the buttocks and in the sacrococcygeal area.
    2. In addition to collections of deeply pigmented dermal dendritic melanocytes, cellular islands .
    3. The cellular blue nevus has a low but definite incidence of malignant transformation; therefore, excision is the treatment of choice.
A combined nevus is the association of a blue nevus with an overlying melanocytic nevus.
The blue-gray that is characteristic of these nevi is an optical effect caused by dermal melanin.
  1.  Achromic Nevus (Nevus Depigmentosus)
    1. These nevi are usually present at birth; they are localized macular hypopigmented patches or streaks, often with bizarre, irregular borders.
    2. They can resemble hypomelanosis of Ito clinically, except that they are more localized and often unilateral. Small lesions may also resemble the white leaf macules of tuberous sclerosis.
    3. They appear to represent a focal defect in transfer of melanosomes to keratinocytes. (congenital, stable, dermatomal)
  2. Epidermal Nevi
    1. These may be visible at birth or may develop within the first months or years of life.
    2. They affect both sexes equally and usually occur sporadically.
    3. Epidermal nevi are hamartomatous lesions characterized by hyperplasia of the epidermis.
  3. Nevus Sebaceus
    1. Small, sharply demarcated, oval or linear, yellow-orange, elevated plaque that is usually devoid of hair and occurs on the head and neck of infants. With maturity, usually during adolescence, the lesions become verrucous and studded with large rubbery nodules.
    2. These nevi form from pluripotential primary epithelial germ cells, which can dedifferentiate into various epithelial tumors.
    3. These nevi are frequently complicated by secondary malignancies and benign adnexal tumors, most commonly basal cell carcinoma or syringocystadenoma papilliferum.
  4. Becker Nevus
    1. Predominantly in males, during childhood or adolescence, initially as a hyperpigmented patch.
    2. The lesion commonly develops hypertrichosis, limited to the area of hyperpigmentation.
    3. The most common sites are the upper torso and upper arm.

Fig: Becker’s nevus

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