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Congenital melanocytic nevi
Medical expert of the article
Last reviewed: 07.07.2025
Congenital melanocytic nevi (syn.: birthmarks, giant pigmented nevi) are melanocytic nevi that exist from birth. Small congenital nevi do not exceed 1.5 cm in diameter. Large congenital nevi are nevi larger than 1.5 cm in diameter. Giant congenital nevi occupy an entire segment of the body surface.
Congenital melanocytic nevi are raised above the skin level, sometimes so slightly that it is noticeable only when examined in transmitted light. They are often unevenly pigmented, often have an uneven relief, and can be palpated to reveal more compacted, often hyperpigmented, nodular areas and areas of softer consistency. Such nevi are usually covered with coarse hair. With age, they can increase in size, their color sometimes fades; perineveous vitiligo may develop.
[ Pathomorphology
Congenital nevi are usually mixed. Deep localization of nevi cells is characteristic, right down to the lower third of the reticular layer of the dermis, and involvement of the epithelium of skin appendages - hair follicles, sweat glands, and muscles that raise the hair - in the process. It is possible to detect nests of nevus cells inside or around vessels. Some congenital nevi of small sizes may not differ histologically from ordinary acquired nevi.
In giant congenital nevi, melanocytes penetrate into the subcutaneous tissue and even fascia. Focal proliferation of Schwann cells of the neurofibroma type and focal cartilaginous metaplasia are possible.
Histogenesis
Giant congenital nevi are considered to be hamartomas of complex structure.
Basal cell nevus syndrome
Basal cell nevus syndrome (syn. Gorlin-Goltz syndrome) is inherited in an autosomal dominant manner and is characterized by five main features: multiple superficial basaliomas, which often quickly become aggressive; epithelial-lined jaw cysts; various skeletal abnormalities, especially of the ribs, skull, and spine; ectopic calcification; small depressions (1-3 mm) on the palms and soles,
Histological examination of the depressions revealed acanthosis, hyperkeratosis at their edges, thinning of the stratum corneum in the center, and proliferation of basaloid cells at the base.
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