A child is born with congenital melanocytic nevi.
You are called to the newborn nursery to evaluate a healthy vigorous newborn with a large dark brown area on the back of the scalp and neck (Figure 1). The anxious first-time parents are tapping on the nursery window as you examine the child.
The most widely accepted classification of CMN is according to size. Small CMNs are defined as measuring less than 1.5 cm, medium are 1.5 to 19.9 cm, and large or giant are greater than 20 cm.3 A CMN is also considered large if it affects a significant portion of an anatomical area, if it is predicted to grow to 20 cm by adulthood, or if the nevus covers greater than 1% of the total body surface area in the head or neck, or 2% elsewhere in the body.2 This distinction may be as important as the size of the CMN when discussing treatment and prognosis.3
Congenital melanocytic nevi are diagnosed clinically by their size (even small lesions are usually bigger than acquired nevi); round or oval configuration; increased coarse dark hair; and smooth, regular well-demarcated borders. The clinical appearance may evolve with age, and is variable in each individual. In neonates, leathery plaques in shades of brown or black are typical, but blue, red, or pink shades may be present. Although many nevi will darken during infancy, many will lighten as they become rougher, more elevated, and/or warty in texture in toddlers and school-age children.4 Parents are often particularly worried about increasing coarse and dark hair and the development of variably pigmented papules, nodules, and plaques in medium to large nevi.
Café au lait macules are always pigmented and flat, as are lentigines. Transient neonatal pustular melanosis (TNPM) can result in dramatic freckling in characteristic areas on the torso. However the pigmented macules in TNPM often have surrounding peeling scale initially, and then salt-and-pepper-like pigmentation, which disappears within the first few weeks of life. Epidermal nevi tend to be warty and uniformly brown in color, and follow the lines of Blaschko. Nevus sebaceous in dark-pigmented individuals may be confused with nevocellular nevi in the newborn, but sebaceous nevi tend to be yellow-orange in color and have a smooth waxy surface. Vascular malformations in dark pigmented infants can usually be distinguished by the purple-red color, which blanches with pressure.
Large congenital melanocytic nevi (LCMN) have been reported with scoliosis, spina bifida, clubfoot, cranial bone hypertrophy, and neurofibromatosis.5 However, most children do not have associated findings.
RISK OF MALIGNANCY AND COMPLICATIONS
Although the lifetime risk of melanoma in patients with LCMN is unknown, recent figures of 2.5% to 5% (in comparison of old literature suggesting a risk approaching 50%) seem reasonable.6 However, the risk may actually be lower, because of biases inherent in collecting data on these individuals. Some investigators have reported that the greatest risk is within the first five years of life, with 50% developing by age three to five, and 70% before age 10. Data from the New York University-LCMN Registry have demonstrated that all patients who developed malignant melanoma had LCMN in an axial location. No malignant melanomas were found in LCMN on the extremities or arising from satellite lesions. Some studies have demonstrated a statistically significant association between a large number of satellite lesions (more than 10) and the risk of developing malignant melanoma.
Neurocutaneous melanosis (NCM) or leptomeningeal melanocytosis (LM) is a rare complication of LCMNs in which there is a proliferation of melanocytes in the leptomeninges. Melanoma may develop in the central nervous system when these melanocytes undergo malignant degeneration. Signs and symptoms of NCM may be due to increased intracranial pressure, mass lesions, or spinal cord compression. They include abnormal reflexes, hydrocephalus, and papilledema.5,7
Most patients who present with NCM have LCMN in a posterior axial location with involvement of the head, neck, and/or trunk, and have numerous satellite lesions. Cerebrospinal cytology and magnetic resonance imaging (MRI) with gadolinium contrast enhancement are the most sensitive studies to diagnose NCM. MRI screening should be performed between four to six months of age, when the anesthesia risks are decreased and before normal myelination of the brain obscures melanin deposits.1