Grading Melanocytic Dysplasia: Updated Histopathologic Criteria

Abstract

Dr. Martin C. Mihm, Jr.'s innovative work on the dysplastic nevus achieved a milestone in his chapter in the World Health Organisation Classification of Skin Tumours (WHO-C). WHO-C presents a dichotomous classification (high-grade versus low-grade dysplastic nevi) and a quantitative metric to assess melanocytic nuclear enlargement. The Duke classification is a related approach that provides mostly quantitative histopathologic criteria for dysplastic nevi and gives due weight to architectural features as well as cytology. This paper proposes and illustrates updated criteria for scoring and grading melanocytic dysplasia, incorporating some of the definitions and categories of WHO-C, while refining the quantitative and architectural elements of the Duke grading system to facilitate more detailed and precise assessment of dysplastic nevi.

Keywords: dysplasia; dysplastic; grading; melanocytic; nevus.

FIGURE 1

Architectural disorder. A. Asymmetry Score 0 (minimal). Dashed red line represents axis by which asymmetry is evaluated. Note that a lesion with minimal asymmetry is equivalent to a highly symmetrical lesion. B. Asymmetry Score 3 (high). Dashed red line represents axis by which asymmetry is evaluated. C. Border imprecision Score 0 (low, 0 borders imprecise), with discrete melanocytic nests at each peripheral border. The red arrows indicate sharply circumscribed peripheral junctional nests. Note that a lesion with low border imprecision is equivalent to highly precise or well‐circumscribed borders. D. Border imprecision Score 3 (high, ≥ 4 borders imprecise). The border of the lesion is imprecise because it is not formed of well‐defined nests; single melanocytes (red box) extend to the periphery as shown at left of panel D. E. Dyshesion Score 0 (low, 0%–25%) The great majority of melanocytic nests are tightly aggregated. Note that a lesion with low dyshesion is equivalent to a highly cohesive lesion. F. Dyshesion Score 3 (high, > 75%). The melanocytic nests are only loosely aggregated, with many clear spaces between melanocytes (red box). G. Confluence Score 0 (low, 0%–25%). Melanocytic nests are discrete and do not exhibit significant confluence. H. Confluence Score 3 (high, > 75%). There is a marked tendency for melanocytes to run together (red box). I. Suprabasal (pagetoid) spread Score 0 (absent). The melanocytes are confined to junctional nests and the epidermal basal layer. J. Suprabasal (pagetoid) spread Score 3 (high, present in ≥ 4 peripheries). The red box highlights a suprabasal melanocyte in the granular layer. K. Single‐cell (lentiginous) spread Score 0 (low, 0%–25%). The melanocytic proliferation is predominantly arranged in nests rather than as single cells. L. Single‐cell (lentiginous) spread Score 3 (high, > 75%). Melanocytes at the basal layer are mainly arranged as individual cells rather than aggregated in nests.

FIGURE 2

Cytological atypia. A. Nuclear size Score 0 (low, melanocyte: Keratinocyte ratio ≤ 1). Yellow arrow indicates control basal‐layer keratinocyte. Red arrow indicates melanocyte similar in size to keratinocytes. B. Nuclear size Score 3 (high, melanocyte: Keratinocyte ratio > 2.0). Yellow box on left indicates control basal‐layer keratinocytes. Red box on right indicates melanocyte with greatly enlarged nucleus. C. Cell size Score 0 (low, melanocyte: Keratinocyte ratio ≤ 1). Yellow box on left indicates control basal‐layer keratinocytes. Red box on right indicates melanocytes similar in size to keratinocytes. D. Cell size Score 3 (high, melanocyte: Keratinocyte ratio > 2.0×). Yellow box on left indicates control basal‐layer keratinocytes. Red box indicates enlarged melanocytes. E. Nuclear pleomorphism Score 0 (low, 0%–5%). Melanocytic nuclei are relatively uniform in size and shape. F. Nuclear pleomorphism Score 3 (high, > 50%). Red boxes highlight marked variation in nuclear size of melanocytes. G. Nucleolar prominence Score 0 (low, 0%–5%). Melanocytes have inconspicuous nucleoli. H. Nucleolar prominence Score 3 (high, > 50%). Red arrow indicates melanocyte with prominent nucleolus. I. Nuclear chromatism Score 0 (low, normal). Melanocytic nest with normal chromatism. J. Nuclear chromatism Score 3 (high). Melanocytic nest with hyperchromatic and irregularly‐chromatic nuclei.