Melanocytic neoplasms

According to the WHO classification (1995), the following varieties of melanocytic nevi are distinguished: borderline; complex (mixed); intradermal; epithelioid and / or spindle cellular; nevus from balloon-shaped cells; halonews; giant pigmented nevus; fibrous papule of the nose (involutional nevus); blue nevus; cellular blue nevus.

[1], [2], [3], [4], [5], [6]

[7], [8], [9], [10], [11], [12], [13], [14]

Conventional acquired melanocytic nevi

Conventional acquired melanocytic nevi (syn: pigment nevi, birthmark) - benign melanocytic neoplasms. Each nevus passes through several stages in its development. At first it is a borderline, intra-epidermal nevus that looks like a uniformly pigmented spot of brown or black with a smooth surface, not palpable. It usually appears in children in the first years of life, but is especially active - in adolescence. Most often located in open areas of the body-face and body. Gradually increases in size, but as a rule, the diameter at this stage does not exceed 5 mm. Over time, the nevus becomes epidermo-dermal, or mixed, while it is much more convex, on average does not exceed 7 mm, is a papule with clear contours or papillomatous formation on the foot, but less intensely pigmented - it is light brown and even solid colors. The surface of the nevus is smooth or uterus. Being an exophyte education, a mixed nevus is prone to injury, with an active growth it may feel itchy. Then the mixed nevus is transformed into an intradermal nevus, which also rises above the surface of the skin, although it can flatten and sometimes completely lose the pigment, acquiring a solid or pinkish color, especially in the case of a pronounced vascular component. The subsequent development of the dermal nevus removes from several years to several decades, up to its involution.

In rare cases, spontaneous immunologic mediated regression of melanocytic nevi with the development of perivoneous vitiligo is possible (see Galonevus)

Pathomorphology

In the borderline, the presence of nevomelanocyte nests in the epidermis at the level of the dermo-epidermal border is determined, especially at the ends of the epidermal outgrowths. Lentiginous proliferation of melanonites is possible. The nevus cells are usually larger than normal melanocytes, with rounded or, much less often, elongated cores, small basophilic nucleoli, with abundant light cytoplasm, in which there may be a large amount of pigment. A refractive artifact is observed, thanks to which the melanocytes of the nevus do not adhere to the surrounding keratinocytes. In cases where the nevus is strongly pigmented. The elimination of melanin through the overlying layers of the epidermis is determined.

At the stage of mixed nevus, nevomelanocytes migrating to the dermis more or less evenly over the entire area of the nevus are defined as nests predominantly in the papillary dermis. Mixed nevus is a symmetrical formation, clearly delimited from surrounding tissues, the epidermal component of the nevus does not go beyond the dermal.

A sign of good quality is the so-called nevus maturation from the outside to the interior. Some authors in the histological architectonics of the mixed nevus distinguish three types of cells: cells of type A, relatively large, located in the upper parts of the dermis, have a cuboidal shape, abundant cytoplasm, containing a different amount of pigment. Cells of type B, located in the middle parts of the dermis, are much smaller in size than cells of type A, melanin does not contain, are arranged as aggregates. Cells of type C, lying in the lower parts of the dermis, are spindle-shaped, arranged in the form of bundles and strands separating the interlayers of connective tissue (neirotized nevus).

At the stage of the dermal nevus, nevomelanocytes are found only in the dermis, mostly cells of the type B and C. In the long-existing dermal nevi and with their involution, the following changes are observed: fibromatous, angiomatous, neuromatous, replacement of nevus cells with mature fat tissue. Often in the papillomatous nevi, so-called pseudovascular cavernous spaces are identified, sometimes with the presence of giant multinucleated cells in them.

At all stages of the evolution of conventional acquired melanocytic nevi, atypism of cells, mitosis, necrosis and lymphocytic reaction are not characteristic.

Immunomorphological investigation in most nevi cells reveals a positive reaction to the antigen S-100.

Histogenesis

According to current ideas, the fact of primary, though temporary growth of nevi cells in relation to surrounding tissues testifies in favor of their evaluation as a neoplasm rather than a developmental defect. The nevus cells differ from normal melanocytes by the lack of shoots, the ability to group into "nests" (groups of 3-5 cells or more), and accumulate pigment in the cytoplasm, as well as a tendency to migrate from the basal layer of the epidermis to the dermis.

[15], [16], [17], [18]

Fibrous papule of the nose

Fibrous papule of the nose (syn: involutional nevus) is a solitary formation of corporal color, projecting above the surface of the skin, hemispherical, usually not exceeding 5 mm in diameter. It can be located anywhere on the skin of the linden, but mostly - on the skin of the nose, sometimes bleeds after a minor injury.

Pathomorphology

The histological picture is very similar to angiofibroma. The dermis is fibrotic and hyalineized, a large number of vessels with enlarged lumens are revealed. Characterized by the presence in the stroma of the formation of a number of fibroblast-like and stellate cells, sometimes there are multi-nuclear cells. In the epidermis there is often lentiginous proliferation of melanocytes.

Histogenesis

Earlier fibrous papule of the nose was considered a fibrous nevus and is still mentioned in the WHO classification in the group of melanocytic nevi. However, the data of electron microscopy and immunohistochemical studies disprove this opinion. At present, formation is thought to be a consequence of the reactive proliferation of dermal dendritic cells on the basis of detection in the dermis of fusiform and stellate cells in which the factor XIIIa and vimentin are detected.

Galonevus

Galoneuvus (Settton's nevus nevus) is clinically a pigmented nevus, surrounded by a zone of depigmentation in the form of a halo, the bowl develops on the skin of the back in children and young people. Can spontaneously regress, leaving behind a depigmented site.

Pathomorphology

In halonews, depending on the stage of the nevus destruction process, lymphoid elements (mainly CD8 + T lymphocytes) either show a continuous lymphocytic infiltrate in the dermis without signs of melanocytic proliferation, or single nevomelanocytes or their clusters in the epidermis and dermis, sometimes with the presence of pronounced cellular atypism . In the surrounding epidermis, respectively, the depigmented aureole around the nevus, melanocytes of the basal layer are destroyed.

Histogenesis

Circulation of antibodies to malignant melanoma cells was noted in patients with regressive halonews. There is also direct immunofluorescence of halonews cells with serum of patients with halonews or malignant melanoma. Electron microscopy revealed that all non-viable cells inside the infiltrate are destroyed. Some lymphocytes are transformed into plasma cells. The data of O. Stegmaier et al. (1969) indicate that nevus cells produce antigen and that infiltrate lymphocytes secrete antibodies against these cells, destroying them.

Nevus from balloon-like cells

The nevus of balloon-shaped cells is extremely rare, usually at a young age. Clinically it does not differ from the usual melanocytic nevus.

Pathomorphology

The nevus cells have a light cytoplasm, and their size is usually increased by a factor of 10 compared to conventional cells, the nuclei do not differ from the nuclei of the nevus cells and are located either in the center or displaced; there are multinucleated balloon cells. The number of balloon-shaped cells varies, they can only be part of the intradermal, as well as mixed, nevi, or there are a lot of them. In the first case balloon-shaped cells are arranged as a node or scattered among ordinary nevus cells. In the second case, they are located alveolar or in the form of foci, in which they do not have cellular boundaries.

Histogenesis

According to some data, the formation of balloon-shaped cells is a consequence of dystrophic processes in nevus cells.