Blue naevi

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).

Click here for example images of this condition

Reference:

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