Giant Congenital Nevus_1211 Derm Dx 2
A 6-month-old boy is brought in for a routine dermatology checkup. He was born with a large brown patch covering most of his right thigh. Some areas of the patch have excessive hair. The patient is otherwise healthy, and there is no family history of skin diseases or skin cancers. Mom is asking if her baby will develop a skin cancer. What’s your diagnosis?Submit your answer, and then read the full explanation below. If you like this activity or have a suggestion, tell us about it in the comment box at the bottom of the page.
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Congenital melanocytic nevi are defined as melanocytic nevi that are present at birth. They are classified by size as “giant,” “medium” or “small.” For an adult, small is defined as less than 1.5 cm in diameter, medium is between 1.5 cm and 19.9 cm and giant is larger than 20 cm. In newborns, larger than 9 cm on the scalp or 6 cm on the trunk is considered giant. Giant congenital nevi are quite rare, with an estimated incidence of 0.005%.1
Giant congenital melanocytic nevi appear most commonly on the trunk but can cover any large area of the body. The giant nevi appear as dark and sometimes hairy patches. Smaller patches, termed “satellite nevi,” may be scattered around the giant nevus. Individual lesions can have variations in color and may develop papules, nodules and other changes within the nevus over time. 1,2
Besides the potential for cosmetic disfigurement, patients with giant melanocytic nevi have the additional complications of increased risk for developing melanoma and neurocutaneous melanosis. The incidence of developing melanoma within the giant nevi is estimated to be between 2% and 15%, with the majority developing within the first 10 years of life.
Neurocutaneous melanosis is the presence of a giant nevus in association with leptomeninges melanosis or melanoma. Risk is greater with axial lesions and is positively correlated with the number of satellite nevi.
Neurocutaneous melanosis can be asymptomatic, or patients may develop symptoms due to hydrocephalus or a mass effect. About half of patients with symptomatic neurocutaneous melanosis develop leptomenigeal melanoma. These melanomas portend a very poor prognosis. 1,2
Diagnosing giant congenital nevus is largely clinical; however, skin biopsy will show diagnostic features. Additionally, any atypical areas that develop within the giant nevus should be biopsied and evaluated for melanoma.
Patients with neurologic symptoms should undergo magnetic resonance imaging (MRI) and evaluation for neurocutaneous melanosis. MRI may be considered in asymptomatic patients with giant nevi in an axial location or with extensive satellite lesions. However, there is no appropriate therapeutic intervention for asymptomatic neurocutaneous melanosis, so some advocate reserving imaging only for symptomatic cases. 1,2
Due to their large size, treating giant congenital melanocytic nevi remains a challenge. Half of melanomas that develop in giant nevi occur in deep structures; therefore removing the nevi may not decrease the patient’s risk for developing melanoma. Some advocate only close observation.
Surgical options include staged excisions. For those who wish to attempt to improve the appearance of giant congenital melanocytic nevi, options include treatment with CO2, Q-switched Nd:YAG, ruby or alexandrite lasers; curettage; and dermabrasion.
All patients should be followed closely with lifelong skin checks and general medical exams at regular intervals. 1,2
Adam Rees, MD, is a graduate of the University of California Los Angeles School of Medicine and a resident in the Department of Dermatology at Baylor College of Medicine in Houston.
1. Bolognia, J, Jorizzo JL, Rapini RP. “Chapter 112: Benign Melanocytic Neoplasms.” Dermatology. 2008: Mosby/Elsevier; St. Louis, Mo.
2. William JD., Berger TG, Elston DM et al. “Chapter 30: Melanocytic Nevi and Neoplasms.” Andrews’ Diseases of the Skin: Clinical Dermatology. 2006: Saunders Elsevier; Philadelphia.