What is blue naevus?
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:
- Common blue naevus
- Cellular blue naevus
- Amelanotic blue naevus
- Combined blue naevus
- Sclerosing (desmoplastic) blue naevus
- Epithelioid naevus
- Subungual blue naevus.
Blue naevi (see below for dermatoscopic views)
Who gets blue naevi?
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.
What causes blue naevus?
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.
What are the clinical features of blue naevus?
The common blue naevus is a solitary, bluish, smooth surfaced macule, papule or plaque. They are generally round or oval in shape.
- The common blue naevus is usually 0.5–1 cm in diameter. The cellular blue naevus is more nodular and is at least 1 cm in diameter.
- The colour of blue naevi can also vary, usually being composed of blue to grey hues, but they are sometimes brown or yellowish.
- Blue naevi are usually found on the distal extremities (dorsum of hands and feet), buttocks, scalp and face although they can occur anywhere on the body.
- Subungual blue naevus grows below the nail matrix and does not cause longitudinal melanonychia. It presents a blue macule within the lunula or under the nail plate.
- They have rarely have been reported in the vagina, the spermatic cord, the lymph nodes, the uterine cervix, the prostate and the oral mucosa.
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.
What are the complications of blue naevus?
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).
How is blue naevus diagnosed?
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.
Dermatoscopic views of blue naevi (see clinical views above)
What is the differential diagnosis for blue naevus?
The differential diagnosis of blue naevus includes:
- Traumatic tattoo
- Combined naevus (a blue naevus combined with a compound melanocytic naevus)
- A vascular lesion such as venous lake
- Cutaneous metastasis
- Kaposi sarcoma
What is the treatment for blue naevus?
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.
What is the outcome for blue naevus?
Unless surgically removed, blue naevi usually persist lifelong.