nevus n : a blemish on the skin formed before birth [syn: birthmark] [also: nevi (pl)]

English

Noun

1. A general term referring to a number of different, usually benign, pigmented lesions of the skin.

   Most birthmarks and moles fall into the category of nevi.

Nevus (or naevus, plural nevi, from nævus, latin for birthmark) is the medical term for sharply-circumscribed and chronic lesions of the skin. These lesions are commonly named birthmarks and moles. By definition, nevi are benign. Histologically, nevi are differentiated from lentigos (also a type of benign pigmented macule) by the presence of nests of melanocytes, which lentigines (pl. form of lentigo) lack.

Classification

• Melanocytic nevus (nevomelanocytic nevus, nevocellular nevus): benign proliferation of melanocytes, the skin cells that make the brown pigment melanin. Hence, most nevi are brown to black. They are very common; almost all adults have at least one, usually more. They may be congenital or acquired, usually at puberty. The melanocytic nevi are classified as such:
  • Junctional nevus: the nevus cells are located along the junction of the epithelium and the underlying dermis. A junctional nevus is flat and brown to black.
  • Compound nevus: a mixture of junctional and intradermal proliferation. Compound nevi are slightly raised and brown to black.
  • Intradermal nevus: the nevus cells are located in the dermis only. Intradermal nevi are raised; most are flesh-colored (not pigmented).
  • Dysplastic nevus (nevus of Clark): usually a compound nevus with cellular and architectural dysplasia. They tend to be larger (more than 6 mm), with irregular borders and irregular coloration. Hence, they ressemble melanoma, appear worrisome and are often removed to clarify the diagnosis. Dysplastic nevi do not transform into melanoma but are a marker of risk when they are numerous (atypical mole syndrome).
  • Blue nevus: the nevus cells are very deep in the dermis.
  • Spitz nevus: a distinct variant of intradermal nevus, usually in a child. They are raised and reddish (non-pigmented). A pigmented variant, called the nevus of Reed, typically appears on the leg of young women.
  • Giant Hairy Nevus: these large, pigmented, often hairy congenital nevi can be a source of much psychological and social suffering. They are also important because melanoma may occasionally (10 to 15%) appear in them.
  • Intramucosal nevus: junctional nevus of the mucosa of the mouth or genital areas. In the mouth, they are found most frequently on the hard palate.
  • Nevus of Ito and Nevus of Ota: congenital, flat brownish lesions on the face or shoulder.
  • Mongolian spot: congenital large, deep, bluish discoloration on the back of Asian babies.
• Epidermal lesions:
  • Epidermal nevus: congenital, flesh-colored, raised or warty, often linear lesion, usually on the upper half of the body.
  • Nevus sebaceus: variant of epidermal nevus on the scalp presenting as a hairless, fleshy or yellowish area.
• Connective tissue lesions:
  • Connective tissue nevus: fleshy, deep nodules. Rare.
• Vascular lesions. See birthmark for a more complete discussion:
  • Hemangioma (strawberry mark or nevus).
  • Nevus flammeus (port-wine stain).
  • Spider angioma (nevus araneus).
  • Blue Rubber Bleb Nevus Syndrome: dilatation of veins anywhere in the body (both skin and internal organs), usually lethal from internal hemorrhage. It is a very rare genetic disorder.

External links

• Atlas of Pathology Section of a melanocytic nevus

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