Melanocytic nevi are benign melanocytic formations of the skin, composed of melanocytes arranged in epidermal nests or clusters, each consisting of an aggregation of three or more melanocytes in close contact. Besides the epidermis, nevi may extend into the dermis. The melanocytes forming the nevi are classified according to their location as epithelioid (superficial), nevus cells (upper dermis), and spindle-shaped (deep dermis). Commonly, nevi are known as moles.
Nevi may be present at birth (congenital nevi) and continue to appear throughout life. However, new nevi most frequently emerge during the first three to four decades of life, with a particular increase during adolescence, followed by gradual regression that can lead to their complete disappearance.
Therefore, while the appearance of new nevi is common in young individuals, their appearance in older age groups is unusual and warrants examination by a dermatologist, especially for any new melanocytic lesion after age 60, to exclude malignancy.
The origin of common nevi is largely unknown and remains an area of ongoing research. Both genetic and acquired factors appear to contribute to their development. Current data show that in the majority of melanocytic nevi (80%), mutations in the B-RAF gene are present, which likely play a central role in their pathogenesis. Additionally, predisposing factors for the appearance of nevi include chronic UV exposure, sunburns, blistering skin diseases (e.g., Stevens-Johnson syndrome, Epidermolysis Bullosa), immunosuppression (chemotherapy, solid organ or bone marrow transplantation, HIV), hormonal therapies and disorders (Addison’s disease, thyroid disorders), pregnancy, phototherapy, heredity, and others.
Furthermore, studies have shown that phenotypic characteristics such as skin and hair color significantly influence the total number of nevi in an individual. For example, research indicates that people of African descent tend to have fewer nevi, while individuals of Caucasian descent, due to lower tolerance to ultraviolet radiation, tend to have a higher number of nevi.
Common melanocytic nevi exhibit great variability in appearance. Most normal nevi are round or oval in shape, and may be either raised or flat with clear borders and homogeneous coloration. Their color is usually some shade of brown.
Melanocytic nevi consist of congenital (or present at birth) nevi and acquired melanocytic nevi (which appear during childhood and adolescence). The family of congenital nevi includes the cellular nevus, while the acquired group includes common melanocytic nevi, blue nevi, Spitz nevus, Reed nevus, as well as a special group called dysplastic nevi.
Sutton nevus
A melanocytic nevus surrounded by a white halo (depigmented zone), often unnoticed in individuals with lighter skin except during summer when the skin is tanned. Common in children and young adults, it results from an immune reaction against the nevus. They are often multiple and commonly appear on the back. This phenomenon may occur on more than one nevus simultaneously. Over time, the central nevus disappears, leaving a depigmented patch. According to literature, individuals with Sutton nevi have a relatively increased risk (18-26%) of developing vitiligo compared to the general population.
Meyerson nevus
A melanocytic nevus surrounded by an inflammatory zone resembling eczema and may be itchy. Meyerson nevi may coexist with Sutton nevi, but the central nevus does not disappear in Meyerson nevus. In most cases, the Meyerson nevus is benign.
Blue nevus
Characterized by a bluish or blue-black color. The blue color results from the Tyndall effect of light scattering in the dermis, where melanin is located deeper than usual in the dermoepidermal junction. Blue nevi are acquired and appear during childhood and adolescence. They should remain stable in size and be regularly examined for changes. Sudden appearance in certain areas, such as the buttocks (cellular blue nevi), warrants excision and histological examination. They are usually found all over the body, with more than half occurring on the backs of the hands and feet, followed by the trunk and face.
Spitz nevus
A heterogeneous group of acquired melanocytic lesions composed of epithelioid or spindle-shaped cells with abundant cytoplasm and large nuclei. It usually appears in childhood as a red, raised nodule that grows rapidly and then stabilizes with a characteristic dermoscopic pattern. Common sites are the face and legs but can appear anywhere on the body. In children, it is often red; in adults, it appears more pigmented, resembling blue nevus or melanoma. Spitz nevus requires regular monitoring in both children and adults, with removal recommended upon any atypia.
Reed nevus
Similar to Spitz nevus (dermoscopic star pattern) but with an average onset age of 25 and darker pigmentation. Usually benign, but excision may be recommended to exclude malignancy. More common in females.
Dysplastic or atypical nevus
Observed in 10% of Caucasians, often on sun-exposed areas like the back, and is a risk factor for melanoma. Criteria for dysplastic nevus include:
- Diameter over 5 mm
- Entirely or partially flat
- Two of the following: asymmetry, irregular shape, indistinct borders, color heterogeneity
Dermatologists evaluate dysplastic nevi and classify cellular atypia as mild, moderate, or severe. Management ranges from observation to treatment depending on individual assessment.
Ota nevus
Congenital, usually unilateral, affecting the first and second branches of the trigeminal nerve. Typical locations include the forehead, periorbital area, conjunctiva, and tympanic membrane. Laser treatment can address the cosmetic concerns.
Ito nevus
Clinically similar to Ota nevus but affects the acromioclavicular nerve area, appearing on the deltoid, supraclavicular, and scapular regions.
Becker nevus
Appears in childhood or adolescence anywhere on the body as a slightly brown, hairy hyperpigmented patch measuring 2–40 cm.
Congenital melanocytic nevi
Present at birth or within the first two years of life, classified by size:
- Small (up to 1.5 cm)
- Medium (1.5–20 cm)
- Large (>20 cm)
They may show hair growth, nodules, or ulcerations and sometimes resemble melanoma. Congenital nevi grow with the child, including hair growth. Small and medium nevi require regular dermatologic monitoring for atypia, while large nevi, due to increased melanoma risk (which develops subepidermally), should be removed.
Removal of nevi and sending them for histological examination is necessary when there is suspicion of malignancy. This is the only way to definitively exclude or confirm its presence. However, a nevus may also need to be removed for cosmetic reasons or when it causes discomfort in daily life, for example, if it is irritated by clothing, jewelry, or shaving due to its location. Depending on the individual case, the nevus’s location, its classification, and the patient's medical history, the treating dermatologist will recommend the most appropriate removal method. Removal of a nevus can be performed by:
- Surgical excision: Suspicious nevi should always be surgically removed with healthy margins to avoid altering the microscopic appearance of the excision margins. The resulting wound is closed with sutures.
- CO2 laser removal: This technique is used only when there is no suspicion of malignancy and the nevus is removed for cosmetic reasons or due to frequent trauma. Laser excision usually leaves no scar.
- Shave excision: The nevus is removed precisely at its margin to minimize trauma and achieve the best cosmetic outcome. Hemostasis can be achieved with electrocautery or CO2 laser.
The best method for prevention and monitoring, especially for individuals with a large number of moles who cannot self-monitor for clinical changes, as well as for those with fewer moles, is mole mapping performed by a dermatologist.
During this procedure, full-body photographs of the moles are taken, followed by dermoscopy using specialized equipment by the treating dermatologist. The frequency of this examination, typically every six months or annually, is individualized and recommended by Dr. Theocharis S. Preventive mole mapping enables periodic evaluation of mole size and microscopic structure, comparison of past and new images at each visit, analysis and grading of malignancy risk, detection of changes in existing moles, and identification of new moles. After all, the best prevention starts with proper patient education from the doctor.
The ABCDE method is a recognized dermatological approach that helps identify suspicious lesions with the naked eye. If we observe any of the following clinical changes in a mole:
- Asymmetry
- Borders (Irregular, scalloped, or poorly defined edges clearly distinct from the surrounding skin)
- Color (Uneven color ranging from light brown to dark brown)
- Diameter (Larger than 6 millimeters)
- Evolution (Changes in size, color, or shape)
We must immediately inform the treating dermatologist for further investigation and examination.