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Melaniform nevus

 
, medical expert
Last reviewed: 04.09.2021
 
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A nevus or a mole - a skin formation made of modified cells of the skin pigment melanin - is defined by domestic dermatologists as a melaniform nevus, which can be acquired or congenital. [1]

On the issue of terminology and classification

Part of the definition "formal" (from Latin - formis) in clinical terminology means "similar, similar".

In the Russian-language version of ICD-10 (in the section on benign neoplasms), the melaniform nevus (pigmented, hairy and blue) has the code D22. Also, depending on the localization, the melaniform nevus of the lip has the code D22.0; the nevus of the eyelid is coded D22.1, and the ear - D22.2; melaniform nevus of the scalp and neck - D22.4; melaniform nevus of the face (its unspecified parts) - D22.3; melaniform nevus of the trunk - D22.5.

In addition, a mole located on the peripheral parts of the body can be defined as an acral melaniform nevus, and the nevus on the upper limb has the code D22.6, and on the lower limb - D22.7.

There is also the term "melanocytic nerus". And the question arises, what does melanoform and melanocytic nevus mean, what is the difference between them?

The fact is that in the original English-language classification - International Classification of Diseases (ICD 10) - the nevus is defined as melanocytic (there is no term "melanoform" at all). And a melanocytic nevus is the same mole on the skin, a benign neoplasm or an  epidermal nevus , consisting of the same melanocytes (lat. - melanocyte), which are often called nevocytes, that is, nevus cells.

Epidemiology

On average, an adult of a Caucasian race can have from one to four dozen melaniform (melanocytic) nevi, with most of the formations located on the body above the lumbar region.

In childhood and adolescence, the number of moles gradually increases, the peak of their appearance falls on the period of 18-25 years. [2]

Causes of the melanoma nevus

The main causes and possible risk factors for the appearance of melaniform nevi are discussed in detail in the publications:

Melaniform nevus in children of the first year of life is rarely observed (on average, in 5-7% of infants). [3]Read:

Pathogenesis

The process of formation of nevi - nevogenesis - is explained by a complex interaction of genetic factors and environmental factors (exposure to ultraviolet radiation, etc.).

The pathogenesis of congenital nevi is associated with disturbances in the formation of melanocytes from precursor cells - melanoblasts of the neural crest of the embryo. Dendritic melanocytes, which carry pigment into the surrounding skin keratinocytes, and nevus cells (nevocytes) are morphologically different types of cells. [4]

According to modern models of neogenesis, melanocytic skin neoplasms arise from one mutated cell, the activation of which leads to the proliferation of melanocytes and their transformation into nevocytes. Pigmented nevus cells in the upper layer of the dermis and epidermis have an epithelioid appearance with a cuboid or oval shape, diffuse cytoplasm and a round or oval nucleus; nevocytes in the middle layers of the dermis are smaller in size and do not contain melanin, and the nevus cells of the lower layers of the dermis have a spindle-like shape, like in fibroblasts.

At the same time, the formation of nevi is seen as a connection with gene mutations of the signaling protein NRAS (which is involved in the regulation of mitosis - cell division); proteins BRAF (serine-threonine kinase), FGFR-3 (fibroblast growth factor receptor), etc.

And these changes at the gene level so affect the transcription factors and signaling pathways (cell transduction) that there is a violation of the proliferation and differentiation of melanocytes. [5]

Symptoms of the melanoma nevus

A growth on the skin is the first sign of a melaniform (melanocytic) epidermal nevus. It can be nodular, located at the junction of the epidermis and the underlying dermis - in the dermoepidermal layer; can be slightly raised above the surface of the skin, as well as intradermal, which is a classic mole - a raised dome-shaped bulge on the skin surface from light brown to dark brown, varying degrees of bulge and size, round or irregular in shape.

There are different types of melaniform nevus, that is,  types of moles on the body , the external symptoms of which may differ.

Melanocytic or melanocytic pigmented nevus is an acquired melanocytic nevus that occurs in childhood as brown flat spots 1-2 mm in size, which most often appear on skin exposed to ultraviolet rays. In these nevi, nevocyte nests are located along the dermoepidermal junction.

If the area of the pigmented formation exceeds 10-12 mm, an extensive melanoform nevus is determined. For example, the size of  Becker's nevus  (hairy epidermal nevus) can be up to 15-20 cm.

Intradermal melaniform nevus or  convex mole  refers to acquired formations that are localized mainly on the head, neck or upper body. In this case, nevocytes can be limited to the middle layer of the dermis. These intradermal nevi are usually fleshy in shape, can have a leg and develop in three stages: first, the mole grows intensively (and can form a leg), then its growth slows down and stops, after which the formation - as the depth of the dermis increases - begins to decrease and becomes lighter...

The border intradermal nevus is  flat and may be gray to brown in color. Also read -  Flat moles

For  nevus Setton  characterized by the appearance of depigmented ring around moles. And the nevus of Jadasson-Tiche (blue epidermal nevus) looks like a dense papule or nodule of blue-gray or blue-black color.

What is a melaniform papillomatous nevus or a verrucous nevus, for more details, see the materials:

A mixed melanoform nevus is determined by the  histology of a mole ; in such cases, in one formation, a combination of various nevus cells, as well as connective tissue and dermal elements, is revealed.

Biopsy and histological examination can also reveal an atypical melanoform nevus - a pigmented melanocytic formation on the skin with distinct clinical and histological features in the form of cellular atypia. More details in the article -  Dysplastic nevi

Complications and consequences

Complications and consequences of melaniform nevi are associated with their damage (trauma), which can lead to bleeding and / or the development of inflammation.

In addition, some moles have an increased risk of malignant transformation into melanoma, therefore, any changes in their size, shape or color should be consulted with a doctor. [6]

For details see:

Diagnostics of the melanoma nevus

Differential diagnosis

Differential diagnosis includes vulgar warts, Clark's nevi (dysplastic melanocyatal nevi), nevoid melanocytic neoplasms of the skin, melanoma. [7], [8]

Treatment of the melanoma nevus

Surgical treatment, that is, removal of a melanoform nevus by surgery  [9] , is discussed in detail in the articles:

Prevention

To date, there are no preventive measures to prevent the appearance of nevi, but it is recommended to avoid prolonged exposure to the sun and not visit tanning salons.

Forecast

For most people, the prognosis of a melaniform nevus is favorable, but one should take into account the possibility of malignancy of these skin neoplasms, which are initially benign.

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