Blue nevus

Blue nevus (syn.: blue nevus of Jadassohn). A distinction is made between common and cellular blue nevi.

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Pathogenesis

In a common blue nevus, spindle-shaped and dendritic cells containing melanin in the form of large, clearly distinguishable granules are found in the dermis, due to which the processes are outlined at higher magnification. The nuclei may be poorly visible due to the abundance of pigment. There are no mitoses or atypia of the cells. The cells are located rather randomly between collagen fibers, often at a large distance from each other, there may be very few of them; sometimes they are found in the walls of blood vessels and in nerve fibers. At the same time, a slight proliferation of fibroblastic cells may be observed.

The cellular blue nevus is characterized by a larger area, usually occupying the entire thickness of the reticular layer of the dermis, as a rule, has a characteristic configuration in the form of an "hourglass" - it forms limited tumors in the dermis and subcutaneous tissue, connected by a narrow isthmus. The nevus is formed mainly by spindle-shaped cells and is characterized by a two-phase nature - alternation of cells with light cytoplasm and heavily pigmented ones. The cell nuclei are usually monomorphic, without pronounced nucleoli or signs of atypism. Single mitoses can be observed. Pigmented melanocytes with long processes are found along the periphery. indistinguishable from the cells of an ordinary blue nevus. It is believed that the presence of these cells is mandatory for diagnosing a cellular blue nevus.

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Symptoms blue nevus

They are benign intradermal melanocytic tumors with characteristic clinical and morphological manifestations. The blue-black color is due to the optical effect and is associated with the deep location of melanin in the dermis.

In typical cases, a common blue nevus is a slightly elevated, symmetrical papule of blue-black color, with a smooth surface, even, but not always clear contours. On average, the size of a nevus is from 4 mm to 1 cm. It is found mainly on the face, back of the hands and back, in the sacral region, more often in newborns and young children. Cellular blue nevi clinically resemble common blue nevi, often develop at a young age, but are congenital, slowly increase in size for some time, can reach several centimeters in diameter, then remain stable. Often protrude significantly above the surface of the skin. Ulceration and bleeding are not typical. The preferred localization is the lumbosacral region, head and neck. Multiple eruptive blue nevi occur. Rarely, cellular blue nevi can become malignant.

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Diagnostics blue nevus

During immunomorphological examination, nevus cells stain positively for S-100 and HMB-45 antigens.

Histogenetically close to blue nevi are intradermal melanocytic nevi of Ota and Ito. They usually exist from birth, but sometimes pigmentation appears only in early childhood. They are more common in women.

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