Giant Bathing Trunk Nevus

A 26-year-old woman came to our hospital with extensive pigmentation of her skin extending from her neck up to her buttock. On examination, the giant pigmented area on her back was more than 20 cm in diameter. She also had similar pigmentation on her face, superior extremity and inferior extremity. The pigmentation was present since her birth. The histopathological changes were characteristic of bathing trunk nevus. Bathing trunk nevus is caused by localized genetic abnormalities resulting in proliferation of melanocytes [1]. Bathing trunk nevus is smaller in infants and children, but it usually continues to grow with the child. It is called a giant bathing trunk nevus when it is larger than 8 inches. 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 lipoma, neurofibroma, spina bifida or other nevi [2]. Malignant melanoma may develop within congenital melanocytic nevi. 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 during childhood. The risk is higher with larger or giant congenital nevi located on the back or abdomen. Rarely, bathing trunk nevi occur with a condition that causes a growth of pigment-producing cells in the meninges (leptomeningeal melanocytosis) [2, 3]. Complications include hydrocephalus, seizure and motor abnormality. Most nevi do not need specific treatment [4]. Treatment involves frequent examinations to check for skin cancers. When possible, surgery to remove the nevus should be done with skin graft as needed. Larger nevi may need to be removed in several stages. Lasers and dermabrasion can also be used to improve the appearance [5]. However, using these techniques may not remove the entire birthmark, and may make it harder to diagnose skin cancer (melanoma). Psychological treatment can help with the emotional impact of having a disfiguring disorder. It may be useful for follow-up to have taken a close-up photograph of the mole with a ruler beside it.

1. Tannous ZS, Mihm MC Jr, Sober AJ, Duncan LM. Congenital melanocytic nevi: clinical and histopathologic features, risk of melanoma, and clinical management. J Am Acad Dermatol 2005; 52:197-203.
2. Bett BJ. Large or multiple congenital melanocytic nevi: Occurence of neurocutaneous melanocytosis in 1008 persons. J Am Acad Dermatol 2006; 54:767-777.
3. Congenital melanocytic nevi. In: Habif TP, ed. Clinical Dermatology. 5th ed. Philadelphia, Pa: Saunders Elsevier; 2009: pp. 850-851.
4. Bittencourt FV, Marghoob AA, Kopf AW, Koenig KL, Bart RS. Large congenital melanocytic nevi and the risk for development of malignant melanoma and neurocutaneous melanocytosis. Pediatrics 2000; 106:736-41.
5. Hale EK, Stein J, Ben-Porat L, Panageas KS, Eichenbaum MS, Marghoob AA, et al. Association of melanoma and neurocutaneous melanocytosis with large congenital melanocytic naevi–results from the NYU-LCMN registry. Br J Dermatol 2005; 152:512-7.