blue naevi

Last reviewed 01/2018

These are benign localised intradermal melanocytes which generally appear as solitary, deeply pigmented, blue-black nodules. They may appear at any age but are more common in the young. A peripheral location is most common, usually the face, hands or feet. The mongolian spot is a variant seen on the sacral area of dark skinned babies.

Blue naevi usually exist in three clinical forms:

• common blue naevus – is a small blue-black papule, usually located on the dorsa of the feet or hands. Histologically, it is characterized by the presence of clumped dendritic melanocytes in mid to lower dermis.
• cellular blue naevus – is similar to common blue naevus, but it is a larger lesion on the sacrococcygeal region or the buttocks. It differs histologically from common blue naevus by the presence of large, pale, spindle-shaped cells in addition to the dendritic melanocytes.
• combined form – so called because it shares the histological features of common blue and naevocytic naevus.

Rarely, multiple, grouped blue naevi may coalesce to give the appearance of a plaque-type blue naevus. These are usually benign lesions, but they can clinically simulate malignant melanoma. Therefore, histological analysis is essential to confirm the clinical diagnosis (1).

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Reference:

• (1). Madan V, et al. A collection of blue papules. Clin Exp Dermatol. 2009;34(1):121-2.