The mother of this 5-month-old boy was concerned about the large birthmark in the infant's diaper area. This lesion is a bathing trunk congenital melanocytic nevus, writes Dr Sunita Puri of Decatur, Ala.
These pigmented nevi, which can vary in size, may occur on the scalp, buttocks, arms, legs, or trunk; the lesion can cover a large area. Their color can vary from tan to dark brown or black; over time, these nevi can darken and coarse terminal hairs may develop within.
An associated congenital anomaly, such as spina bifida, leptomeningocoele, or neurocutaneous melanosis, may be present. Hydrocephalus and seizures can develop in patients with neurocutaneous melanosis.
Early treatment is recommended. When technically possible, full-thickness prophylactic excision and grafting is advised; a 2% to 16% incidence of malignant melanoma is associated with these nevi.1 In this patient, biopsies at various sites did not reveal melanoma; however, because of the risk of malignant degeneration, the parents were advised to schedule regular follow-up examinations with biopsies for the patient.
1. Hurwitz S. Clinical Pediatric Dermatology: A Textbook of Skin Disorders of Childhood
and Adolescence. 2nd ed. Philadelphia: WB Saunders Company; 1993:165.