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WHO Classification of Tumours
Superficial congenital melanocytic nevus


Congenital melanocytic nevi (CMN) of the superficial type are melanocytic proliferations of small size (<1.5 cm) present at birth. Some congenital melanocytic naevi which may not be apparent at birth (tardive congenital melanocytic naevi).
Superficial congenital melanocytic nevus may be found on any part of the body. It presents as a macular, papular or plaque-like lesion with a smooth or papillated surface. The colour varies from light brown to black. A characteristic histological feature is the presence of dense diffuse infiltrates of small monomorphous melanocytes in the upper part of the dermis and the mid-portion of the reticular dermis. The melanocytes are frequently arranged in single files between collagen bundles ("splaying of melanocytes"). An important diagnostic criterion is the presence of melanocytes along epithelial structures of adnexa and their angiocentric distribution.
Congenital melanocytic nevi, biopsied shortly after birth or in the first years of life, can display atypical intraepidermal changes similar to those of melanoma in situ. The pathogenetic role of superficial congenital melanocytic nevi as precursor lesions of malignant melanoma is controversial. Some studies report an etiological association

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Barnhill RL, Fleischli M (1995)
Histologic features of congenital melanocytic nevi in infants 1 year of age or younger.
J Am Acad Dermatol 33: 780-5

.However, clinical follow-up of 3922 patients with superficial/ small CMN found no significant risk of melanoma development
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Berg P, Lindelöf B (2003)
Congenital melanocytic naevi and cutaneous melanoma.
Melanoma Res 13: 441-5

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LeBoit PE, Burg G, Weedon D, Sarasin A (Eds.)
World Health Organization Classification of Tumours. Pathology and Genetics of Skin Tumours
3rd Edition
IARC Press: Lyon 2005