Polarized light-surface microscopy for description and classification of small and medium-sized congenital melanocytic naevi.

Owing to a lack of well-defined clinical criteria for identifying congenital lesions, the diagnosis of small and medium-sized congenital melanocytic naevi is always uncertain. Our aim was to describe the features of small congenital melanocytic naevi, as observed by digital videomicroscopy, with the purpose of identifying single patterns characteristic of small congenital melanocytic naevi or different morphological subgroups. We could then perform a classification based on their macroscopic and surface microscopic aspects. Digital images referring to 154 small congenital melanocytic naevi and to 150 acquired naevi were examined for pattern analysis. New features characterizing small congenital melanocytic naevi, such as target network, target globules, target vessels and focal thickening of network lines, were identified, and a subdivision of small congenital melanocytic naevi into different subgroups was performed. Discriminant analysis enabled the distinction between congenital and common naevi with a sensitivity of 82.5% and a specificity of 64%. Small congenital melanocytic naevi can be described and classified by digital videomicroscopy and pattern analysis. The most important discriminant features are target network, small globules, follicles and vessels. This classification may represent a useful tool in the follow-up of small congenital melanocytic naevi.