Bathing trunk naevus

Congenital melanocytic naevi are found in 1% of newborn babies. They are often small - less than 5 cm in diameter - and pale brown. In time, they may darken and develop an outgrowth of terminal hair. The lesions are mostly flat, but sometimes raised naevi are also seen (1).

Congenital melanocytic naevi are present from birth, but in some cases, they might not be evident at birth due to the lack of visible pigment. They become visible only after the development of pigment, months to years from birth (2).

Giant congenital naevi occur in 1 in 20 000 live births. Bathing trunk naevi, which are even larger, occur in 1 in 500 000 live births (3).

The bathing trunk naevus is a rare type of congenital naevus characterised by dark brown pigmentation over a large part of the trunk. Often, there are associated smaller congenital naevi. The risk of malignancy is thought to be higher for these giant naevia than for the other smaller congenital naevi. A useful prognostic factor is the predicted size of the congenital naevus lesion in adulthood (1).

Large congenital melanocytic naevi (especially, the presence of large numbers of associated satellite naevi) also carry an increased risk of neurocutaneous melanocytosis (4).

Management of congenital melanocytic naevi must be tailored for each patient and each naevus, taking into consideration (5):

• the risk for developing malignancy
• the risk for developing symptomatic neurocutaneous melanocytosis
• cosmetic implications of having the naevus and the cosmetic implications of any resultant surgical scars from their removal
• adverse effects that the naevus may have on psycho-social development
• adverse effects and long-term sequelae of any surgical intervention

Reference:

• (1). McLaughlin MR, et al. Newborn Skin: Part II. Birthmarks. Am Fam Physician. 2008;77(1):56-60
• (2). Changchien L, et al. Age- and Site- Specific Variation in the Dermoscopic Patterns of Congenital Melanocytic Nevi. Arch Dermatol. 2007; 143(8):1007-1014
• (3). Leech SN, et al  Neonatal Giant Congenital Nevi With Proliferative Nodules. Arch Dermatol. 2004; 140:83-88.
• (4). Marghoob AA, et al. Number of satellite nevi as a correlate for neurocutaneous melanocytosis in patients with large congenital melanocytic nevi. Arch Dermatol. 2004;140:171-175
• (5). Marghoob AA, et al. Congenital Melanocytic Nevi: Treatment Modalities and Management Options. Semin Cutan Med Surg. 2007;26(4):231-40