Nevus - Congenital Melanocytic
Congenital melanocytic nevus is present at birth, in about 1% of all newborns and persists throughout life. Congenital nevus varies widely in size and can be several centimetres in diameter and rarely may cover almost the entire skin. However, most congenital nevi are small, almost always over 1 cm, and much resemble the acquired nevi.
This type of nevus is round or oval shaped with spots on the surface of the skin and its tone can vary from slightly pigmented like a sunburn tan to medium or deep brown. Congenital nevus is divided into small (<1.5 cm), medium (1.5-10 cm), and giant (>20 cm). Often within the nevus there are two shades, and the darker one is located in the centre. In some cases, the congenital nevus may have hairs on it.
The main concern regarding congenital nevus is its precancerous potential. There is certainly an increased risk of developing malignant melanoma on such nevi. This possibility is greater in giant congenital nevi. Nevertheless, the risk from congenital melanocytic nevi is low.
Nevus – Acquired Melanocytic
Melanocytic nevi (common moles) are small clearly defined acquired melanocytic spots or papules. Depending on the location of the cells that make up this type of mole, the following forms can be distinguished in:
Moles - Associated Melanocytic:
These nevi are spots or lesions that protrude slightly. The colour of the nevi is light brown or dark brown, with an even distribution of pigment. They are round or oval in shape with smooth borders. The location of these nevi is usually random, although they are clearly more often found on areas exposed to the sun (trunk, arms, legs, sometimes the palms and soles).
A nevus with connective activity has little potential for malignant outgrowth. This in such a nevus is rare, considering that the average person has at least 25 nevi on his/her body.
Moles - Mixed Melanocytic:
They are usually dark-colored moles that protrude. The shape of this type of nevus is round, dome-shaped, smooth, sometimes papillomatous or hyperkeratotic and may have hairs on it. They are most commonly found on the face, head, torso and limbs.
Moles – Melanocytic Choroidal:
This type of moles usually protrudes the skin, may be brown, light brown or skin-colored, and are round or dome-shaped. They are usually developed on the face and neck, but they can also be found on the torso or limbs. They rarely disappear.
Moles - Alveolar Melanocytic or Sutton Nevus:
This is a type of nevus usually brown or light brown in colour which is surrounded by a band of discolouration. This nevus often disappears automatically. It may be a precursor of vitiligo as about 18-26% of people with this nevus may also develop vitiligo. The presence of white algae around a nevus is an immune response of the skin trying to fight the nevus. Because many melanomas also develop such a zone of discoloration, the diagnosis of such a mole should be made very carefully by a dermatologist.
A blue nevus is an acquired, benign cyan or greyish-black lesion or nodule that usually occurs in childhood or late adolescence. This type of nevus needs close monitoring as in some cases it can lead to malignant melanoma of the skin.
A Spitz nevus is a benign, dome-shaped, hairless small nodule of a pink or light brown colour. The characteristic feature of this nevus is that it grows and enlarges rapidly within a few months. It is common in children and its location is mainly on the head and neck.
A spilocytic nevus is a melanchromatic spot that has numerous smaller dark brown spots or papules on it. This nevus can lead to melanoma in 5% and therefore close monitoring and nevus removal is required.
Becker's nevus is a skin disorder that primarily affects men. This type of nevus initially appears as an irregularly shaped dark spot on the arm or upper torso (although it can also be found on other areas of the body), which gradually grows irregularly and may have thick and dense hairs on the surface. It can be present at birth, but is usually first noticed around puberty.
Ota's nevus is a spotted dark skin plaque which may be blue or dark brown in colour. It is a very common nevus in Asian populations and may be present at birth but is not hereditary. Its distribution is mainly in the periocular area and the maxillary region. When this nevus is located on the shoulder it is known as Ito's nevus. Nevus of Ota is a benign melanosis that primarily involves the region of the trigeminal nerve distribution. The Nevus of Ito is quite similar to Nevus of Ota in its appearance. However, it is different in the pigmentation and does not appear on face.
Epidermal nevus occurs from birth or within the first decade of life and may increase in size dring adolescence. Epidermal nevus is skin-coloured and is most commonly found on the upper part of the body. It has no malignant potential.
Comedo nevus is the manifestation of an abnormality of the hair follicle resulting in the appearance of many phagospores arranged in a linear pattern. It usually occurs in childhood or adulthood as a single lesion, which is linear and located on the face or appears as multiple lesions on the neck, trunk and arms.
A sebaceous nevus is a healed yellow or orange hairless plaque surrounded by many small scabs. The most common location for this type of nevus is the scalp.
The sebaceous nevus occurs at birth and is a tumor sensitive to androgens. It increases in size during childhood like sebaceous glands, but then regresses until puberty where it again increases to reach its maximum size. Because there is a risk of future progression to basal cell skin cancer, preventive removal of nevus in the second or third decade of life is recommended.
Vascular Nevus / Birthmark
A vascular nevus or nevus is a clearly excreted tumour, bright red in colour and round in shape. This type of nevus may be present at birth or appear shortly afterwards, reaching its maximum size at 6 months of life.
The head and neck are the most common locations for the nevus, but it can appear on any other part of the body. It is most common in premature infants and is thought to be an abnormality of fetal angioblasts development. The vascular nevus may occasionally bleed, which usually resolves with local pressure. If this type of nevus does not fully resolve spontaneously then its remnants can be surgically removed in the second decade of life. Alternatively, treatment with systemic corticosteroids and/or B-blockers may help in childhood, especially for bleeding vascular nevi with severe symptoms.
The Soft Hemangioma (Port-Wine Stain) is not a genuine type of nevus. It is a vascular lesion usually flat red in colour and irregular in shape which varies in size and is usually unilateral. The nevus is present at birth and can be located anywhere on the body, but is most commonly found on the face and neck.
A Mongolian spot is not a genuine type of nevus, it is a greyish lesion typically found on the lumbar region, but it can also appear on the scalp or anywhere on the skin. It is usually an isolated lesion, but rarely are there several lesions on the trunk from birth. The nevus disappears on its own after a certain period of time.