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| Nevocellular Nevus |
| Etiology •Developmental anomalies |
| Pathogenesis •A nevus or a nevocellular nevus is a benign proliferation of melanocytes originating from the neural crest. •Nevi show three distinct morphologies, which characterize their development. •The most primitive is the junctional nevus, characterized by a benign proliferation of nevus cells along the dermo-epidermal junction. •These cells have all the features of melanocytes, including the production of large quantities of melanin, the presence of dendritic processes and the expression of dopa hydroxylase. •More developed nevi show evidence of hyperplasia with cords and nests of cells extending into the dermis. •Nevi that show both junctional proliferation and the presence of proliferating nevus cells in the dermis are referred to as compound nevi. •Even more advanced nevi lose connection to the epidermis and exist primarily as proliferating masses, nests and cords of cells in the dermis alone. •These are called dermal nevi. •As the cells mature, they become less dendritic and lose dopa hydroxylase and the ability to generate pigment and instead, become more elongated and resemble nerve cells and express nerve specific enzymes, including choline esterase. •Many purely dermal nevi may have relatively little pigment., |
| Epidemiology •Very common •All of us have several of these benign lesions |
| General Gross Description •Morphologically, nevi can appear either as flush lesions (mostly junctional nevi) or as fleshy lesions with more or less hair formation. •Dermal and compound nevi particularly tend form these bulging masses. •Spitz nevi are lesions seen in younger children and tend to be pink, somewhat pedunculated lesions. •Halo nevi are nevi that are pigmented and have a surrounding area of depigmentation. |
| General Microscopic Description •Histologically, the lesion is characterized by the presence of proliferating melanocytes which, depending on the development, may be only along the dermal-epidermal junction, mixture of dermal-epidermal junction and dermis or purely dermal. •As indicated earlier, the junctional nevi are characterized by dendritic cells with pigment, whereas the more dermal tend to be nests of elongated cells resembling nerve cells. •The important histological features that distinguish a nevus from a malignant melanoma is the presence of a uniform nuclei, the absence of prominent nucleoli, the lack of invasion of the epidermis and the absence of radial spread. •A halo nevus has a central nevus and a rim of lymphocytes. |
| Clinical Correlation •Nevi are benign •The possibility of "degeneration" into malignancy is complicated and may occur in certain histological types and in individuals with a family history. |
| References • Cotran RS, Kumar V, Robbins SL: Robbins Pathologic Basis of Disease. 5th edition. Philadelphia, W.B. Saunders, 1994, pp. 1176. |
| Nevocellular Nevus |
| Synopsis by: T.V.Rajan, M.D., Ph.D. (T01000M87500)[523] |
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