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Naevus caeruleus – Blue Nevus Explained

Naevus caeruleus is a benign blue-grey pigmented skin lesion caused by deeply situated melanocytes in the dermis. It is generally considered harmless.

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Things worth knowing about "Naevus caeruleus"

Naevus caeruleus is a benign blue-grey pigmented skin lesion caused by deeply situated melanocytes in the dermis. It is generally considered harmless.

What is Naevus caeruleus?

Naevus caeruleus, commonly known as the blue nevus, is a benign pigmented skin lesion resulting from the accumulation of melanocytes (pigment-producing cells) deep within the dermis (the lower layer of the skin). Its characteristic blue-grey colour arises from the Tyndall effect: light is scattered and reflected by deeply located melanin particles, giving the lesion a bluish appearance even though the pigment itself is brown-black.

Causes and Development

The exact cause of naevus caeruleus is not fully understood. It is believed that the melanocytes involved failed to complete their normal migration from the neural crest to the epidermis during embryonic development, instead becoming trapped within the dermis. This leads to a congenital or early-acquired misdistribution of pigment cells.

No known external cause (e.g., UV radiation)
Genetic predisposition may play a role
More common in women and in individuals of Asian descent

Appearance and Symptoms

Naevus caeruleus typically presents with the following characteristics:

Colour: blue, blue-grey, or blue-black
Size: usually less than 1 cm in diameter
Surface: smooth, slightly raised or flat
Well-defined borders and uniform pigmentation
Common locations: back of the hand, foot, buttocks, scalp, and face

In most cases, naevus caeruleus causes no symptoms. It is painless and rarely changes over time.

Variants of Naevus caeruleus

Common Blue Nevus (Naevus caeruleus simplex)

The most frequent form, small, round, and well-circumscribed. Considered benign with no significant risk of malignant transformation.

Cellular Blue Nevus (Naevus caeruleus cellularis)

A rarer variant that can be larger (often more than 1 cm) and contains a denser cluster of melanocytes. In very rare cases, this form may undergo malignant transformation into a malignant melanoma.

Diagnosis

Diagnosis is typically made clinically by a dermatologist. The following methods are used:

Dermatoscopy: A non-invasive examination using a magnifying device to assess pigment patterns
Histology: If there is any uncertainty, a tissue sample is taken and examined under a microscope
Differential diagnosis: The lesion must be distinguished from other pigmented lesions such as melanoma, haematoma, or Mongolian spot

Treatment

A common naevus caeruleus does not usually require treatment, as it is benign. Removal may be considered in the following situations:

Changes in size, shape, or colour
Unclear diagnosis or suspicion of malignancy
Cosmetic concerns of the patient

Removal is performed by surgical excision, and the excised tissue is routinely sent for histopathological examination. Laser therapy is an option but is less recommended, as it does not allow for histological analysis of the removed tissue.

When to See a Doctor?

The following changes should be evaluated by a doctor promptly:

Increase in size or change in shape
Change in colour or uneven pigmentation
Bleeding, crusting, or itching
Development of new similar lesions

References

Braun-Falco's Dermatology (7th Edition) - Springer Medicine
Tschandl P. et al. - Dermatoscopy of Pigmented Lesions, Journal of the American Academy of Dermatology, 2019
World Health Organization (WHO) - Classification of Skin Tumours, WHO Classification of Tumours, 4th Edition, 2018

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