[Quantitative studies of congenital and acquired nevus cell nevi]

A total of 576 melanocytic naevi routinely excised within 1 year were analysed histologically and epidemiologically without knowledge of the clinical diagnosis. Classification into congenital melanocytic naevi (CMN, n = 82) and acquired melanocytic naevi (AMN, n = 494) was performed on the basis of the clinical history. Only a few CMN, and also some AMN, reached the lower dermis and the subcutis. An affinity of naevus cells (NC) for skin appendages was observed significantly more often in CMN than in AMN. However, no type of skin appendages was exclusively infiltrated by NC of CMN. The NC affinity for different types of skin appendages in a single naevus was characteristic of CMN. A subepidermal zone poor in NC was seen more often in CMN. The broad horizontal layer of NC within the upper dermis was rather rare in both types of melanocytic naevi. In spite of significant histological differences between CMN and AMN, the specificity and sensitivity of each criterion proved to be too low for a reliable histological diagnosis of CMN.