Pathology of Congenital Nevus:

"Brown Birthmark" present at birth.

Dr Sampurna Roy MD       

Congenital nevi are usually found in newborn infants.

These are usually solitary lesions and are mostly located on the trunk. Some congenital nevi are also found on the lower extremities and scalp.

Most of these nevi are usually less than 10 mm in diameter.

Giant congenital nevi are more than 20 mm in diameter.

Melanoma arising in small congenital nevi has a less aggressive growth pattern.

Melanoma arising in giant congenital nevi are usually non epidermal in origin.

The tumour cell patterns include spindle and round cell differentiation, malignant blue nevus and heterologous differentiation. (Example:  Liposarcoma ; Rhabdomyosarcoma etc).

Further reading:

A retrospective cohort study of Southeast Asian patients with large congenital melanocytic nevi and the risk of melanoma development.

The risk of malignancy in large congenital nevi

Congenital melanocytic nevi: clinical and histopathologic features, risk of melanoma, and clinical management

Genetic changes in neoplasms arising in congenital melanocytic nevi: differences between nodular proliferations and melanomas

Speckled lentiginous nevus: within the spectrum of congenital melanocytic nevi

Malignant melanoma simulants arising in congenital melanocytic nevi do not show experimental evidence for a malignant phenotype.

Histopathology of congenital pigmented nevi.

The histology of "congenital features" in early acquired melanocytic nevi.

Immunohistologic patterns of congenital nevocellular nevi.

Congenital smooth muscle hamartoma masquerading as congenital pigmented nevus.

Patterns of congenital nevocellular nevi. A histologic study of thirty-eight cases.