Causes

Bathing trunk nevi are thought to be caused by defects or problems that occur as a baby grows in the womb. However, in some families bathing trunk nevi may be inherited.

A bathing trunk nevus may occur with:

• Growth of fatty tissue cells (lipomas)
• Neurofibromatosis
• Other nevi
• Spina bifida

Smaller congenital pigmented or melanocytic nevi are common in children and lead to fewer complications. Larger or giant nevi are fairly rare.

Symptoms

A nevus will appear as dark-colored patch with any of the following:

• Brown to bluish-black color
• Hair
• Regular or uneven borders
• Small satellite areas (maybe)
• Smooth, irregular, or wart-like skin surface

Nevi are commonly found on the upper or lower parts of the back or the abdomen. They may also be found on the:

• Arms
• Legs
• Mouth
• Mucus membranes
• Palms or soles

Exams and Tests

All birthmarks should be evaluated by your health care provider. A skin biopsy may be taken for examination to determine whether the cells have become cancerous.

An MRI of the brain might be performed if the skin lesion is over the spine. There also may be problems in the brain when a giant nevus is found on the spine.

Treatment

Treatment involves frequent exams to check for skin cancers.

When possible, surgery to remove the nevus will be done. Skin grafting is done when needed. Larger nevi may need to be removed in several stages.

Lasers and dermabrasion can also be used to improve the appearance. However, using these techniques may not remove the entire birthmark, and may make it harder to diagnose skin cancer (melanoma). For these reasons, surgery is controversial.

Psychological treatment can help with the emotional impact of having a disfiguring disorder.

Outlook (Prognosis)

Skin cancer (such as malignant melanoma and other types) may develop in up to 15% (1 out of 6) of people with larger or giant nevi, often in childhood. The risk is higher for larger or giant congenital nevi located on the back or abdomen.

Possible Complications

• Depression and other emotional problems (due to appearance)
• Skin cancer (melanoma)

Rarely, bathing trunk nevi occur with a condition that causes a growth of pigment-producing cells in the head (leptomeningeal melanocytosis). Complications include:

• Hydrocephalus
• Motor abnormalities
• Seizures

When to Contact a Medical Professional

This condition is usually diagnosed at birth. 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.

Alternative Names

Congenital giant pigmented nevus; Giant hairy nevus; Giant pigmented nevus; Bathing trunk nevus; Congenital melanocytic nevus - large

References

Bett BJ. Large or multiple congenital melanocytic nevi: Occurence of neurocutaneous melanocytosis in 1008 persons. J Am Acad Dermatol. 2006 May;54(5):767-777.

Congenital melanocytic nevi. In: Habif TP, ed. Clinical Dermatology. 5th ed. Philadelphia, Pa: Saunders Elsevier; 2009:pp 850-851.

Updated: 4/8/2012

Reviewed by: Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington School of Medicine. Also reviewed by Kevin Berman, MD, PhD, Atlanta Center for Dermatologic Disease, Atlanta, GA. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.