The diameter of congenital melanocytic nevi (CMN) has served as the lone criterion for determining risks of adverse outcomes such as melanoma. A standardized description of additional morphologic features is needed.

We sought to develop a consensus-based standardized categorization of cutaneous features of CMN and to test agreement among experts on the proposed scheme.

An interdisciplinary group of experts in the field of CMN was surveyed using a detailed questionnaire. Applicability of the expert consensus-based scheme was tested for interobserver agreement.

The principal variable of the consensus-based categorization is CMN size, based on maximal diameter the CMN is projected to attain by adulthood. CMN size categories include: small (<1.5 cm); medium (M1: 1.5-10 cm, M2: >10-20 cm); large (L1: >20-30 cm, L2: >30-40 cm); and giant (G1: >40-60 cm, G2: >60 cm). In addition, number of satellite nevi in the first year of life is categorized into none, 1 to 20, more than 20 to 50, and more than 50 satellites. Additional descriptors of CMN include anatomic localization, color heterogeneity, surface rugousity and presence of hypertrichosis (described as none, moderate, marked), and presence of dermal or subcutaneous nodules (none, scattered, extensive). Assessment of consistency among 3 experts showed moderate to excellent interobserver agreement for categorization of the clinical descriptors (kappa values 0.54-0.93).

Applicability of the proposed scheme was tested in a virtual setting and only among experts.

The proposed categorization scheme for CMN was agreed upon by experts and showed good interobserver agreement. Such standardized reporting of patients with CMN facilitates the development of an international clinical database for the study of large and giant CMN.