Nevi are rare at birth; they develop afterwards and new ones can appear up to approximately 40 years of age. They are pigmented lesions that increase with pregnancy and regress with old age.
Schematically, they can be distinguished in junctional, compound and dermal nevi. The dermal nevi or skin moles are often round, raised, with an irregular, wart-like or regular surface, with a light, dark or black colour, sometimes sprouting hairs. The junctional or compound nevi or skin moles are at risk, even though very low, of malignant degeneration.
Their aspect varies very much, but generally speaking, they are flat or slightly raised lesions on the skin, displaying a homogeneous colour, varying from clear brown to black, or with some darker, regular dots. The lesions have mainly a symmetric shape (round or oval), or they display modest asymmetries, they have a regular outline and show normal little skin furrows on the surface. The latter are two important signs to distinguish them from malignant melanoma.
In the last few years, videodermoscopy is the technique that is used more and more in the differential diagnosis among the several types of nevi and, consequently, in the assessment of their risk index. Through a miniaturized camera, this equipment transfers a magnified image of the nevus to be examined on the screen of a computer, enabling the examiner to detect the smallest and finest structural details of the lesion to determine an extremely precise assessment of the risk. It is possible to memorize the image in the computer in order to compare it in time.
Usually, the removal of a nevus, when considered necessary, is performed surgically, also to carry out a histological examination to confirm its nature.