Congenital nevomelanocytic nevi: Proportionate area expansion during infancy and early childhood

Background: The way in which congenital nevomelanocytic nevi (CNN) expand relative to anatomic region during growth is relevant to decisions about optimal timing for surgical excision and assessment for malignant change. Objective: Our purpose was to determine how CNN area expands relative to anatomic region during infancy and early childhood. Methods: Forty-one small CNN in as many subjects were studied from the newborn period. Relative area (CNN area/anatomic region area) was derived for each measure. Proportionate expansion (PE), defined as change in relative area per unit time as a proportion of initial relative area, was calculated. Relative to anatomic region, area expansion of CNN is greater when PE is greater than 0, less when PE is less than 0, and at least double when PE is +1.0 or greater. Results: From the newborn period to last measure (2 to 71 months), PE ranged from −0.7 to +8.8 (median, +0.1). For 66% of CNN (27 of 41), PE was greater than 0. Nine of 39 CNN (15.4%) had PE values of +1.0 or greater during the first 6 months, compared with 1 of 26 cases (3.8%) for the interval beginning at or after 6 months. Conclusion: Disproportionately rapid area expansion of CNN may occur during early infancy, related to transient benign neoplasia, delayed pigmentation, and/or error of the methods used in the analysis.