Patterns of distribution of giant congenital melanocytic nevi (GCMN): The 6B rule

BackgroundGarment-related terms have been used to describe the pattern of distribution of giant congenital melanocytic nevi (GCMN).ObjectiveWe sought to describe patterns of distribution of GCMN and propose a classification scheme.MethodsPhotographic records of patients with GCMN from the Hospital Clinic of Barcelona were analyzed and a classification based on observed GCMN distribution patterns was created. The classification was independently applied by 8 observers to cases found in the literature. The interobserver agreement was assessed.ResultsAmong 22 patients we observed 6 repeatable patterns of distribution of GCMN, which we termed the “6B”: bolero (involving the upper aspect of the back, including the neck), back (on the back, without involvement of the buttocks or shoulders), bathing trunk (involving the genital region and buttocks), breast/belly (isolated to the chest or abdomen without involvement of bolero or bathing trunk distributions), body extremity (isolated to extremity), and body (both bolero and bathing trunk involvement). Our literature search found 113 cases of GCMN, which we were able to classify into 1 of the 6B patterns with an overall kappa of 0.89.LimitationsSome patterns occur infrequently with a dearth of images available for analysis.ConclusionsThe anatomic distribution of GCMN occurs in 6 recognizable and repeatable patterns.