A disfiguring, darkly pigmented, often hairy patch of skin (nevus) that is present at birth and may cover an extremely large area of the body, sometimes covering most of the trunk and the upper arms and thighs.

Alternative Names

Congenital giant pigmented nevus; Giant hairy nevus

Causes, incidence, and risk factors

Bathing trunk nevi are thought to be congenital, but in some families the frequent appearance of these lesions suggests a hereditary component. The surface texture may vary from smooth to warty, and the color varies from brown to bluish black. Bathing trunk nevi may cause psychological (emotional) problems because of their cosmetic appearance. More importantly, the nevus has a high risk of developing into malignant melanoma (a type of skin cancer ). The risk is thought to be between 3% and 7%, although this number varies in different medical studies.

Signs and tests

All birthmarks should be evaluated by your health care provider. A biopsy of suspicious areas may be obtained for pathology (examining the lesion under the microscope to determine if the cells have become cancerous). A special scan, MRI, for the brain might be performed (see leptomeningeal melanocytosis below).

Treatment

Present treatment consists of surgery to remove of the nevus, with skin grafting where necessary. Extremely large nevi are removed in several stages with the possible use of expanders.

Expectations (prognosis)

Except when the nevus transforms into malignant melanoma , bathing trunk nevi are compatible with a normal life span.

Complications

On rare occasion, bathing trunk nevi are associated with a condition called leptomeningeal melanocytosis (growth of pigment-producing cells in the head), which can produce hydrocephalus , retardation, motor abnormalities, and seizures . Bathing trunk nevi can transform to become malignant melanoma .

Calling your health care provider

Call for an appointment with your health care provider (or mention it during a well-baby exam) if your child has a large pigmented area anywhere on the skin.

Prevention

There is no known prevention.