Congenital melanocytic nevus

Congenital melanocytic nevus appears as a circumscribed to black patch or plaque, heterogeneous in consistency, covering any size surface & any part of the body.

Differential Diagnosis: 

  1. Congenital melanocytic nevus
  2. Verrucous epidermal nevus
  3.  Lentigine
  4. Melanoacanthoma


CMN is congenital. There is no verrucosity on the lesions neither is it along a blaschko line. Hence not B. Melanoacanthoma is very rare variant of seborrheic keratosis presenting as a deeply Pigmented proliferation of melanocytes and Keratinocytes over the head, neck and trunk of elderly people.

Large congenital nevi are caused by a mutation in the body’s cells that occurs early in embryonic development, usually within the first twelve weeks of pregnancy. Mutations are sometimes found in genes that code for NRAS and KRAS proteins. There is no known method of prevention.


Congenital melanocytic nevi may be divided into the following types:

  • Small-sized congenital melanocytic nevus is defined as having a diameter less than 2 cm (0.79 in)
  • Medium-sized congenital melanocytic nevus is defined as having a diameter more than 2 cm (0.79 in) but less than 20 cm (7.9 in).
  • Giant congenital melanocytic nevus (also known as “bathing trunk nevus,” “garment nevus,” “giant hairy nevus”, and “nevus pigmentosus et pilosus”) is defined by one or more large, darkly pigmented and sometimes hairy patches.

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