Among the findings that help differentiate CMN from acquired nevus are: presence of nevus cells in the lower two thirds of the dermis and subcutaneous tissue; arrangement of these cells as isolated elements or "in Indian line" among the collagen bundles of the lower reticular dermis; the involvement of sebaceous glands, blood vessels, erector muscles of hair follicles, eccrine glands and lymphatic vessels (typically, the nevus cells are present in many units and more than one cutaneous appendage, nerve or capillary vessel), and also the occurrence of perivascular, perifollicular and / or around the eccrine glands distribution, which often simulates inflammatory infiltrates.The involvement of collagen by nevus cells in the middle and deep reticular dermis is a CMN feature with high sensitivity (85.7% to 98.3%) and specificity (72.5% to 96.7%). The finding of greater specificity, however, reaching 100%, is the occurrence of nevus cells within the sebaceous glands, nerves and blood vessels in the deep reticular dermis.
Giant congenital nevus is a rare neuroectodermal lesion occurring in approximately 1 of every 20,000 newborns. 1 It is usually a compound nevus that extends into the subcutaneous and rarely into the muscle layers. The larger giant nevi have a striking dermatomal distribution. Presumably, this results from the origin of the nevus cells in the neural crest. At birth, these lesions may be light brown, but they darken with time and grow coarse dark hair, and the skin surface roughens.