Naevus (from the Latin naevus), or nevoid tumor, birthmark, nevus – malformation, which is characterized by the appearance on the skin, sometimes on the mucous membranes, conjunctiva (the thin transparent tissue that covers the outside eye) and choroid (middle) layer of the eyeball (iris and choroidea) spots or entities, consisting of the so-called nevus cells.
Nebesnye cells originate during fetal development of the neural crest – a particular set of cells that develop from a variety of anatomical structures (ganglia, meninges, some cells of the adrenal glands, and pigment cells (melanocyte) of the skin). Due to some inadequately explored reason nebesnye cells do not reach maturity melanocyte. The precursors of melanocytes (melanoblasts) migrate to the deep layer of the epidermis (the epidermis – the outer layer of human skin presented stratified epithelium), but some of them do not reach it, and remain in the dermis (connective skin located below the epidermis).
Nevi have been reported in 75% of the representatives of the European race. On the body of an adult human has an average of about 20 moles, but some people have their number may exceed 100. In childhood nevus may be invisible, but during puberty, under the influence of sunlight, as well as during pregnancy may be a manifestation of nevi.
In its development naevus goes through several phases: naevus first is vnutrepenialnymi, then transformed into a border, and over the age of 30 years becomes a phase intradermal. With the onset of old age naevus often subjected to reverse development: nebesnye cells are immersed into the dermis and are transformed, over time, being replaced by connective tissue. Such evolution of the nevus associated with the stages of simplifying the organization and function of melanocytes: melanocyte — newusa cell — fibrous (tough connective) tissue.
Significantly, the vast majority of nevi are acquired, which are divided into ordinary and special types. Among ordinary nevi, in turn, allocate edge, complex (epidermo-dermal) and intradermal form.
Border, or functionally, nevus appears, as a rule, in the first two decades of life and are predominantly located on the face, neck, torso, hands, in some cases, and on the external genitals; is uniformly pigmented (light brown to dark brown) stain diameter of 1-5 mm, maximum 10 mm having a circular or oval shape, smooth surface and clear boundaries. The surface boundary nevus devoid of hair. This form of nevus exist until around the age of 35 years.
Mixed, or compound, naevus is a transitional form from the edge to the intradermal nevus. It can be mostly edge or predominantly intradermal. Mixed naevus has a spherical shape and dense texture, its color may vary from light brown to black, dimensions usually do not exceed 10 mm.
Intradermal nevus is more common in Mature or old age. It can be single or multiple, and are predominantly located on the face, neck, or torso. Intradermal nevus is a domed or warty education, which in form may resemble a berry BlackBerry and have a “leg”. Its dimensions vary from 2 mm to several centimeters, color from pale brown to black, but sometimes occurs depigmentirovannyj (containing pigment) intradermal nevus whitish or pink-red colour.
Localization of conventional nevi in different parts of the body, and especially the location they nevus cells depend for their symptoms: on the palms and soles, where the stratum corneum is thick, complex and intradermal nevi do not protrude above the skin. Towering above the skin nevi are characterized by a pronounced intradermal newsnum component, and flat — edge component. The stronger nevus extends above the skin level, the weaker it pigmented.
Normal nevi increase in size in direct proportion with the growth of the human body. Their number increases after birth and reaches its maximum numbers in the period of puberty, and after 50 years is gradually reduced, and 70-90 years they usually disappear completely.
Congenital nevi are benign pigmented tumors, which consist of nevus cells (derived melanoblasts) arising out of a violation of the process of specialization of melanoblasts during the prenatal period. Congenital nevi have 1% of Caucasians and can be detected at birth or within the first year of a child’s life. They come in different sizes, up to giant. Congenital nevi light brown or dark brown in color, somewhat above the level of the skin, sometimes covered with hair, while hair growth begins immediately. Congenital nevi are round or oval, clear or blurred boundaries, right or wrong form. Their surface can be saved with a skin pattern or rough, wrinkled, folded, lobed, sometimes covered with papillae, resembling brains. They can be located on any area of the skin. In 5% of cases these nevi are multiple, but then one of them is larger. Larger nevi soft to the touch. Congenital nevi in appearance practically indistinguishable from acquired ordinary nevi, the only external difference between them is the diameter more than 1.5 cm (acquired nevi of this size do not reach). Large (more than 20 cm in diameter) and giant congenital nevi is a part of the anatomical region or the whole (torso, limb, head, or neck), but in combination with multiple small congenital nevi. Small congenital nevi in 95% of cases are solitary. Another difference between congenital nevi is that nebesnye cells are located in the deeper layers of the dermis, subcutaneous tissue, in the skin appendages. Congenital nevi, in contrast to acquired, do not disappear spontaneously.
Dysplastic nevus (Clark nevus, atypical nevus) is an acquired pigmented lesion resulting from indiscriminate division of abnormal melanocytes. It occurs in 5% of the population develops on healthy skin or on the background of complex (mixed) nevus, less edge. Dysplastic nevus appears later than acquired nevi — before puberty, during his life, until old age, is usually on the trunk and extremities. Development it contributes to the sunlight. Spontaneous disappearance for the dysplastic nevus is not typical. Dysplastic nevus is intermediate between acquired nevi and superficial spreading melanoma. It looks like the stain with a separate towering above the skin areas that have a large size (more than 15 mm in diameter) and uneven color, which can be mottled to resemble scrambled eggs or a target. Also characterized by asymmetry and irregular borders, fuzzy, jagged edges.
Risk of malignant nevus
The presence of nevi poses some risk of his development of cutaneous melanoma is a malignant tumor that develops from melanocytes. In people with multiple small nevi that risk more than the average. A risk factor is not only the number of nevi on the skin, but also the presence of their forms, protruding above the surface. The occurrence of melanoma is possible after the injury nevus: single (bruises, abrasions, cuts) or chronic (permanent trauma clothing or footwear).
As in 50% of cases of melanoma of the skin develops on the background predshestvuyuschih nevi, they are considered as cancer. There is a direct correlation between the size of the nevi and the frequency of malignant tumors.
In relation to malignancy are the two most dangerous types of nevi: dysplastic and congenital. Under certain conditions, cisplatina nevi can develop into melanoma in 100% of cases. In either congenital nevi can also develop melanoma.
The risk of malignancy of nevi with a diameter more than 2 cm is 5-20%, with special hazards are nevi are located on the face. A person who has 20 nevi, the risk of developing melanoma increases by 3 times.
Methods of treatment and removal of naevus
In most cases, acquired nevi do not require any treatment, but there are indications for their surgical removal:
1. Cosmetic indications (according to the wish of the patient to remove disfiguring naevus).
2. The normal location of the nevus in the difficult self-control locations (for example, on the scalp, perineum).
3. The identification of nevus of these signs of atypia, as uneven distribution of melanin, the graininess of its borders, their vagueness, relatively large diameter (more than 5mm).
4. Atypical nevus development, including a sudden change in shape and size.
5. Nevi with high risk of malignancy (e.g., giant congenital nevus; cisplatina nevi). All small congenital nevi with an unusual appearance (uneven color, irregular shape, etc.), must be surgically removed until the patient is 12 years of age. Surgery to remove a giant congenital nevus is carried out as early as possible.
6. As a prophylactic measure in some cases it is advisable to remove the nevus in a significant number of them as it prevents occurrence of melanoma.
7. Intensely colored nevi peripheral location in the limbs, on the mucous membrane, in the subungual region and conjunctiva: they should be removed, so as cisplatina nevi such localization is alert to their rebirth in melanoma.
8. Frequent repeated irritation and injury of the nevus, such as underneath the belt, bra or collar.
Clearly defined the indications for immediate excision of the nevus. These are signs of a sudden change in the last month or more:
1. Increased area and height of the nevus.
2. The increase of the intensity of pigmentation, especially in those cases where it is uneven.
3. The appearance of the Corolla of pigment around the nevus, the appearance of the elements-satellites.
4. The inflammatory process in the nevus.
5. The emergence of itching.
6. The formation of erosions and cause bleeding.
Removal of nevi should be done by the oncologist, to be radical and conducted only surgical method with the obligatory subsequent histological examination of tissue removed. Partial removal of the nevus is unacceptable, because then naevus repigmented and recur, forming pseudomelanosis. Cosmetic outcome is often in this case, unpredictable, such treatment may lead to the development of relapse with sequelae, less favourable than before treatment.
Such methods of removal, electrocoagulation, cryosurgery, dermabrasion, laser removal in the nevi of the skin and mucous membranes should not be used, as make it impossible for histological confirmation of diagnosis.
Removal of nevi of small size in adults is possible under local anesthesia and is considered a relatively simple surgery that does not require no patient preparation. After excision of the nevus on the edge of the formed skin defect sutures, tightening it from the top for a few days fastens sterile dressing daily during the week are held bandaging, after healing, the stitches are removed.
In operations about nevi larger sizes are formed when extensive skin defects, to close them resort to skin grafting, and surgery is performed under General anesthesia.
All surgical interventions in children are performed only under General anesthesia.
Prevention of malignancy of naevus
Prevention of melanoma in patients with nevi is early and active case-finding premilinary forms (primarily the dysplastic nevus). It is necessary to identify patients with the presence of these forms in the “risk group” and provide constant dynamic change monitoring of these elements, or delete them.
Patients with dysplastic nevi should be aware of the signs of the rebirth of these nevi in melanoma and thus independently regularly monitor the nature of their changes. These patients are advised to avoid sun exposure, and when going outside apply sunscreen.