Clinical Features:

• Nevi that are present at birth, with histologic features that are distinctive from those of acquired nevi
• Often multiple
• Classified into three categories by size: small (less than 1.5 cm), medium (1.5 to 20 cm) and large (over 20 cm)
• Small and medium-sized congenital nevi have a low risk of malignant transformation, whereas large congenital nevi have a substantial risk.
• They are typically flat and light brown at birth, and over time may increase in pigmentation and thickness, sometimes becoming wart like, and may become increasingly hairy.

Histologic Features:

• There is often hyperkeratosis, acanthosis and papillomatosis.
• Congenital nevi tend to extend much deeper into the dermis than acquired nevi, and sometimes extend into the subcutaneous fat along the fibrous septa.
• The melanocytic infiltrate tends to be diffuse, with much less tendency to nest than in acquired nevi, except in the junctional and upper papillary dermal components.
• There is often a grenz zone between the epidermis and the dermal nevus cells.
• Nevus cells surround and often involve the skin appendages.
• Perineural involvement is common, and nevus cells often involve the walls of blood vessels.  These should not be considered features of malignancy if the typical features of a congenital nevus are present.
• The fibrous stroma seen in acquired nevi is typically not present.
• Pigmentation tends to be most pronounced in the upper aspects of the nevus.
• Occasional mitoses may be seen in the papillary dermis.
• In the deeper aspects of the nevus, single cell and Indian-file patterns are often seen.

Cases associated with this book:

Congenital nevus
Author: Artur Zembowicz M.D. Ph.D.

Conference: Dermpedia Teaching Collection

Congenital nevus
Author: Artur Zembowicz M.D. Ph.D.

Conference: DermatopathologyConsultations.com Teaching Collection