Classification of congenital melanocytic naevi and malignant transformation: a review of the literature

Introduction. Congenital naevi (CN) vary greatly in size, macroscopic appearance and histology. There is a practical need to subdivide CN according to size, since size differences have a direct bearing on cosmetic and resultant psychological problems, and on therapeutic options, and probably on the chance of malignant transformation. In this review, we summarise the literature on size subgroupings of CN, with special focus on giant congenital naevi and their risk of malignant transformation. Materials and methods. A Medline literature search from 1966 to October 2002 was performed. Only English-language studies focusing on CN in association with melanoma were included. The final strategy consisted of textwords and medical subject heading (MeSH) terms on small, medium, large and giant congenital naevi combined with the textwords classification, histology and melanoma. Additional manual cross-referencing was performed. We excluded articles that dealt only with aspects of treatments. Results. A wide variety of criteria for size subgrouping of CN has been put forward in the literature and precludes a direct comparison of reported data (Table 1). We identified 35 such articles in the world literature in which no less than seven different definitions of minimum size of a giant CN were employed. Histologically, it is difficult or even impossible to conclude that a naevus is congenital or acquired, especially in case of a small lesion, since the differences are not absolute (Table 2). Giant CN have an increased risk for malignant transformation, but the reported incidence rates have differed widely from one to 31% (Table 3). Reported melanoma incidence rates have derived from retro- and prospective studies, reviews and case reports, and compared with each other using different definitions. On top of this, patients in different age groups were reported, who were registered in different referral centers. Conclusion. To allow comparison of study results from different centers, it is essential that the size subclassification of CN is based on standard and generally accepted criteria. We recommend defining GCN as a CN covering one percent body surface area in face and neck and two percent elsewhere on the body. Based on a review of the world literature, we recommend prophylactic excision of all CN, in close communication with patient and family and individualising treatment accordingly.