Giant pigmented nevus is a congenital benign neoplasm of the skin, which is a pigment spot of large size (more than 20 cm), sometimes occupying a significant part of the limb or trunk. Due to the characteristic appearance, the diagnosis of such a nevus is not difficult. Giant pigmented nevus refers to melanoma-threatening nevi, therefore, its removal is desirable. However, due to the large size, this is not always possible. Patients with non-removed nevus should regularly undergo examinations by a dermatooncologist for timely diagnosis of the onset of its malignant transformation.
The appearance of a giant pigmented nevus is caused by a violation of the differentiation process of melanoblasts occurring in the fetus in the period from the 10th to the 25th week of its intrauterine development. The frequency of birth of a child with such a nevus is 1 in 500 thousand newborns. However, according to some data, giant nevus occurs in 1-2% of the world’s population. The disease can be combined with other congenital anomalies, for example, with hydrocephalus, Recklinghausen’s neurofibromatosis, epilepsy, primary melanoma of the soft membrane of the brain.
Giant pigmented nevus, because of its huge size, often occupies entire anatomical areas. It can be located on the trunk, limbs, neck or head. With its symmetrical arrangement on the torso, a picture resembling a vest appears, a collar on the neck. It is possible to combine a giant nevus with multiple small nevi, which are usually located at some distance from it.
The surface of the giant nevus is uneven, the color can vary from gray and brown to black. Over time, the skin of the affected area thickens and pigmentation increases. At the same time, different areas of the nevus may have different coloring. The surface of the nevus becomes heterogeneous, bumpy and warty. In most cases, hair appears on certain areas of the nevus. Since the giant pigmented nevus grows slowly, as the child grows, there is a relative decrease in the size of the nevus. At the end of adolescence, there is a decrease in the pigmentation of the nevus and the cessation of its thickening.
Like other congenital nevi, a giant pigmented nevus remains on the skin of its owner all his life. Such nevi persist even at a very advanced age, when there is a gradual disappearance of all acquired nevi.
The main complication of the giant nevus is its malignancy and transformation into melanoma. This process can be triggered by various acute or repeated traumatic effects on the nevus: mechanical, radiation (including sunlight), chemical.
The transition of a giant pigmented nevus to melanoma can happen at any age. According to various data, this occurs in 2-13% of cases of the disease. During the transformation of the nevus into melanoma, its accelerated growth, changes in shape and color, bleeding, the appearance of erosions and crusts on the surface are noted.
The diagnosis of a giant pigmented nevus is made possible by its characteristic appearance and the fact that there is a nevus on the skin from birth. Additional studies are needed to detect the transformation of nevus into melanoma in a timely manner. Dermatoscopy and sciascopic examination are most often used for this purpose, allowing to study the structure and edges of the nevus under 10-30-fold magnification. With the help of dermatoscopy, the exact definition of the nevus boundaries is carried out to plan the operation.
The histological picture of giant pigmented nevus, as well as other congenital pigmented nevi, is characterized by the absence of melanocytes in the papillary layer of the dermis and an increase in their content in the basal layer of the epidermis. Nevus cells are detected in the lower layers of the dermis, subcutaneous fat and skin appendages: ducts of sweat and sebaceous glands, hair follicles. With a giant pigmented nevus, nevus cells also penetrate into muscles, bones and meninges.
Despite the large size of the nevus and the infancy of the patients, the best way to treat it is to remove it. Such therapeutic tactics are associated with a high probability of malignancy of the giant nevus, which can occur already in the first year of life. The decision on the operation is made individually, taking into account the location and size of the nevus, the age and state of health of the patient, the degree of possible disability as a result of the operation, etc. If the operation is postponed, then the patient needs constant monitoring by an oncologist with examinations at least once a quarter.
Surgical treatment of giant pigmented nevus is carried out jointly by dermatooncologists and plastic surgeons. It consists in its complete excision of the nevus with the capture of 0.5 cm of healthy skin located on the border with it. If the size and localization of the nevus do not allow it to be removed immediately, a phased excision is performed. The material removed during the operation necessarily undergoes histological examination. The large skin defects resulting from the operation require closure by skin grafting. Plastic surgery can be performed by free skin grafting or autodermoplasty with transplantation of own skin flaps on vascular anastomoses. For plastic closure of the defect, the technology of artificial cultivation of cultures of own epidermis cells on synthetic analogues of the dermis is also used.