Moles are proliferations of pigmented cells called melanocytes, which aggregate taking variables aspects. Moles may be red, red-brown, brown, black or blue, the shapes may vary from round to oval and the size from pinhead to giant dimension. For example congenital nevi can affect an entire limb or part of the trunk (bathing trunk nevus). Moles may be everywhere on the skin and their number is variable, ranging from 10 to 40 nevi per person. Their surface can be smooth or warty, they can be flat or raised, sometimes occur as flat lesions and subsequently they raise, rarely disappear. Moles may be congenital (congenital melanocytic nevi) or may appear later, even though most of the moles occurs around age 20. Sometimes moles can be surrounded by a depigmented ring (Halo nevo or Sutton ’s nevus) and usually the mole disappears leaving a white patch. If the whitish halo has an irregular shape is important to consider that it could be a melanoma. Giant congenital melanocytic nevi are rare and they could be associated with lipomatosis or neurofibromatosis, with meningocele or spina bifida. There are many classifications of moles, but the most ’simple is histopathological and it distinguishes them in:
- Junctional nevi: groups or nests of nevus cells at the dermoepidermal junction and they usually are flat and very pigmented.
- Dermal nevi: nests of nevus cells arranged in the dermis, they are usually dome-shaped and look similar to compound naevi. They may not be any darker than the rest of your skin
- Compound nevi: the nevus cells are both at the dermoepidermal junction They are slightly raised and are often hairy. Their colour can vary from brown/black, to the the color of skin.
Blue naevus was first described by Tiesche in 1906, It appears blue in colour due to the optical effects of light reflecting off melanin deep in the dermis. there are many variants, the common subtype presents as blue or black papules or nodules, rounded, rather firm, usually solitary, less than 1cm in diameter. These are usually located on the head, hands and feet. Histologically, there is a proliferation of elongated, finely branched dendritic melanocytes within the dermis, melanophages (containing large aggregates of melanin). A grenz zone separates the lesion from the epidermis.
Meyerson mole was first described by Meyerson in 1971 and it appears like a melanocytic naevus with eczema. It occurs commonly in young males and it is caused by lymphocytic CD4+ reaction against melanocytic antigens. UV exposure and Interferon alfa 2 b can trigger a Meyerson mole. The therapy is topical corticosteroid creams. The surgery is performed if the dermatologist suspects a melanoma.
Dysplastic nevus is widely debated, it ’s defined like an acquired mole, often large with specific histological characteristics. Dysplastic moles are generally larger than ordinary moles and have irregular and indistinct borders, their color frequently ranges from pink to dark brown; they are flat and sometimes parts may be raised above the skin surface. They are most common on the trunk, abdomen and arms
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