Dysplastic (Clark's) nevi

    Article Contributors: 
    Sean Klepper M.D.
    Stephen Lyle, M.D., ...

    Also known as: atypical melanocytic nevi, B-K moles, melanocytic nevi with architectural disorder and cytologic atypia

    Clinical Features:

    • Highly controversial entity without well agreed upon criteria for diagnosis
    • The presence of dysplastic nevi, particularly when numerous, is a marker for increased risk of melanoma, and dysplastic nevi occasionally develop into melanoma.
    • Predilection for the trunk, scalp, breasts, buttocks and dorsal feet
    • Considerable variation in clinical appearance among nevi, even different nevi on the same patient
    • Tend to be intermediate in size between common nevi and melanomas, and often have irregular borders and variation in color and elevation

    Histologic Features:

    • Most dysplastic nevi are compund, and the remainder are junctional
    • Architectural Features (One of the first two features must be present to make the diagnosis.):
      • Lentiginous melanocytic proliferation: elongation of the rete ridges (often club shaped) with melanocytic hyperplasia and increased epidermal pigment
      • Disordered junctional nesting: variation in size, shape and location of the nests, often with confluence of nest and/or "bridging" of nests between adjacent rete ridges
      • Reduced cohesion between cells within junctional nests
      • "Shoulder phenomenon": the junctional component (in a compund nevus) extends out beyond the border of the intradermal component, and gradually diminishes in cellularity without a clear demarcation
    • Cytologic Features (The first is required to make the diagnosis):
      • Nuclear atypia (with variation in the degree from cell to cell, an important distinction from melanoma [see below]):
        • Nuclear enlargement: a rule of thumb is larger than adjacent keratinocyte nuclei
        • Nuclar pleomorphism
        • Nuclear hyperchromasia
        • Prominent nucleoli
      • Spindled cell pattern
      • Epithelioid cell pattern
      • Abundant pale or dusty cytoplasm
      • Large melanin granules
    • Host Cell Response Features:
      • Lymphocytic infiltrates: These range from scant perivascular infiltrates to dense band-like infiltrates.
      • Dermal fibroplasia
      • Prominent vascularity
    • Dysplastic nevi are commonly graded as to their degree of cytologic atypia, with considerable interobserver variability.  Mildly dysplastic nevi may be difficult or impossible to reliably distinguish from nevi without atypia.  On the other side of the spectrum, severely atypical nevi may be difficult to distinguish from frank melanoma.  General guidelines are:
      • Mild atypia: minimal nuclear enlargement (approximately the same size or very slightly larger than the nuclei of the keratinocytes of the stratum spinosum) with retraction of cytoplasm
      • Moderate atypia: Somewhat larger nuclei, often with visible nucleoli
      • Severe atypia: nuclear enlargement to two times or greater the size of the nuclei of the keratinocytes of the stratum spinosum, prominent nucleoli, abundant granular to dusty (due to fine melanin granules) cytoplasm
    • Distinction of a severely atypical dysplastic nevus from in situ or microinvasive melanoma is often quite subjective and fraught with peril; however, an attempt should be made to classify the lesion when possible.  Features that favor a diagnosis of melanoma rather than severely atypical dysplastic nevus are:
      • Poor circumscription
      • Prominent asymmetry
      • Loss of orderly nesting pattern
      • Effacement of rete ridges
      • Prominent dyscohesion of nests
      • Lack of predilection of the melanocytes for the rete ridges
      • Uniform or nearly uniform degree of cytologic atypia
      • Prominent pagetoid spread
      • Lack of maturation of the dermal component
      • Mitoses in the dermal component
      • Band-like lymphocytic infiltrate
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    Cases associated with this book:

  • Clark's nevus
    Author: Stephen Lyle, M.D., Ph.D.

    Conference: Dr. Z's Consultations