Common Acquired Melanocytic Nevi



Common Acquired Melanocytic Nevi


Christine J. Ko, MD










This junctional melanocytic nevus is an oval macule of even, light brown pigment. There is overall symmetry with a smooth border; the size was measured to be 2 × 1 mm.






This junctional melanocytic nevus shows nests at the tips and sides of rete ridges. The presence of pigmented parakeratosis and pigment incontinence image likely corresponds to a dark color clinically.


TERMINOLOGY


Synonyms



  • Benign melanocytic nevus, junctional melanocytic nevus, compound melanocytic nevus, intradermal melanocytic nevus, common mole, common melanocytic nevus, nevocellular nevus


ETIOLOGY/PATHOGENESIS


Exact Etiology Unknown



  • Believed by some to arise from intraepidermal melanocytes


  • Others suggest that melanocytic nevi arise from nerves or pluripotential cells


Tumor vs. Hamartoma?



  • Still debated


  • Evidence for tumor



    • Studies showing that some nevi are clonal


    • Growth advantage of nevus cells over epidermal, dendritic melanocytes in cell culture


    • Similar expression of different markers by nevi and malignant melanoma


    • Presence of mutations in BRAF oncogene in majority of nevi


  • Evidence for hamartoma



    • Other proliferative elements: Epidermal, follicular, connective tissue


    • Studies showing that some nevi are polyclonal


CLINICAL ISSUES


Epidemiology



  • Incidence



    • Number of acquired nevi



      • Increases with age up to 3rd decade


      • May be related to familial predisposition


      • Sun exposure in childhood also linked to development of nevi


      • More common in lighter skinned individuals


  • Age



    • Not present at birth


    • Majority develop in adolescence


    • Density of nevi generally decreases after 4th decade


Presentation



  • Junctional lesions



    • Flat to minimally raised macule/very thin papule


    • Generally < 6 mm, but may be larger


    • Color often a variation of brown


  • Compound lesions



    • Slightly raised papule


    • Variable color (brown, flesh-colored, pink)


    • May contain hair


  • Intradermal lesions



    • Papule, may be pedunculated


    • Variable color (brown, flesh-colored, pink)


    • May contain hair


Natural History



  • Abtropfung hypothesis of Unna



    • Melanocytes are initially junctional


    • With chronologic time (aging), melanocytes “drop off” into dermis, creating compound melanocytic lesions


    • With more time, the junctional melanocytes have all “dropped off,” creating intradermal melanocytic lesions


    • Intradermal melanocytic lesions may eventually “shed” or become acrochordons



      • Degenerative changes include balloon cell change and fatty change


  • Alternative hypothesis



    • Nevi begin in the dermis


  • Not all melanocytic nevi display progressive changes; some arrest at a given stage indefinitely



Treatment



  • Not necessary


  • Conservative removal (e.g., shave removal) generally sufficient



    • Residual dark pigment may remain


    • Pigment may recur irregularly within scar (recurrent nevus)


Prognosis



  • Benign


MICROSCOPIC PATHOLOGY


Histologic Features

Jul 8, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Common Acquired Melanocytic Nevi
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