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Author: Hon A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand, 1997. Updated by Dr Anita Eshraghi, Dermatologist, Sweden, March 2018.
Blue naevus (nevus in American spelling) is a type of melanocytic naevus in which spindle-shaped or, less commonly, ovoid naevus cells, are located deep within the dermis.
Different types of blue naevus include:
Blue naevi are twice as common in women as in men. They are more prevalent among Asians, where the prevalence is estimated to be 3–5%, compared to approximately 1–2% in white-skinned adults.
Blue naevi derive from an incomplete migration of melanocytes from the neural crest. The blue colour is caused by the Tyndall effect, in which shorter wavelengths of incident light are scattered by the dermal melanocytes. The blue naevus is usually blue in colour because the melanocytes are deeper than those of brown moles.
The common blue naevus is a solitary, bluish, smooth surfaced macule, papule or plaque. They are generally round or oval in shape.
Blue naevi may develop at any age but are rarely present at birth or within the first 2 years of life. The most common age of onset is late childhood or adolescence.
Common blue naevi do not have any complications. They are benign and stay unchanged throughout life.
In contrast, cellular blue naevi can rarely transform into malignant cellular blue naevus (a type of melanoma).
Blue naevi are usually diagnosed clinically by their typical appearance. The diagnosis may be confirmed by finding a homogenous steel-blue ground-glass pattern on dermatoscopy. If there is any uncertainty about the diagnosis, an excision biopsy may be performed. The histopathology of blue naevus reveals spindle-shaped melanocytes in the dermis.
The differential diagnosis of blue naevus includes:
Usually, no treatment is required for a blue naevus.
Blue naevi that are bigger than 1 cm, changing or appearing de novo in an older adult should be considered for histological evaluation to exclude melanoma. Blue naevi in the scalp are often removed as a precaution, because their history is mostly unknown and it is difficult in keep them under review.
A blue naevus can also be surgically removed for cosmetic reasons.
Unless surgically removed, blue naevi usually persist lifelong.
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