Congenital melanocytic nevus: two clinicopathological forms

Area of Science:

• Dermatology
• Pathology
• Genetics

Background:

• Congenital melanocytic nevus (CMN) is a hamartomatous disease with significant functional, aesthetic, and oncologic implications.
• Previous classification attempts for CMN have lacked consistency and repeatability.
• CMN is a known precursor to malignant melanoma, highlighting the need for accurate classification.

Purpose of the Study:

• To propose a new, clinically and pathologically consistent classification system for congenital melanocytic nevus (CMN).
• To differentiate between two distinct types of CMN based on biological, clinical, and histopathological criteria.
• To improve the understanding and management of CMN and its associated risks.

Main Methods:

• Prospective clinical and pathological study of 200 cases of congenital melanocytic nevus (CMN).
• Detailed analysis of lesion characteristics, including size, number, anatomical distribution, and depth.
• Histopathological examination to assess melanocyte distribution and involvement of deeper structures.

Main Results:

• Identification of two distinct types of CMN: Type I and Type II.
• Type I CMN: typically a single, superficial plaque in one anatomical region, growing with the child, with rare melanoma development.
• Type II CMN: multiple lesions, often with a large central plaque, involving deeper structures, associated with neurocutaneous melanocytosis, and higher melanoma risk.

Conclusions:

• The proposed two-type classification system (Type I and Type II CMN) is logical, biologically advantageous, and clinically repeatable.
• This classification provides a framework for better understanding CMN behavior, risk stratification, and patient management.
• Accurate differentiation of CMN types is crucial for predicting melanoma risk and guiding clinical decisions.