My approach to atypical melanocytic lesions

Abstract

Histological assessment of melanocytic naevi constitutes a substantial proportion of a dermatopathologist's daily workload. Although they may be excised for cosmetic reasons, most lesions encountered are clinically atypical and are biopsied or excised to exclude melanoma. Although dysplastic naevi are most often encountered, cytological atypia may be a feature of several other melanocytic lesions, including genital type naevi, acral naevi, recurrent naevi, and neonatal or childhood naevi. With greater emphasis being given to cosmetic results, and because of an ever increasing workload, several "quicker and less traumatising" techniques have been introduced in the treatment and diagnosis of atypical naevi including punch, shave, and scoop shave biopsies. A major limitation to all of these alternatives is that often only part of the lesion is available for histological assessment and therefore all too frequently the pathologist's report includes a recommendation for complete excision so that the residual lesion can be studied. Complete or large excision of all clinically atypical naevi permits histological assessment of the entire lesion, and in most cases spares the patient the need for further surgical intervention.

Figure 1

Banal dermal naevus showing a single mitotic figure. The nuclei are uniform.

Figure 2

(A, B) Clonal naevus. Note the distinct population of pale staining naevus cells and conspicuous melanophages in the reticular dermis.

Figure 3

Melanoma (left side of field) arising in a congenital naevus from the scalp.

Figure 4

(A) Close up view of a circumscribed, expansile tumour nodule (left). (B) Note the large vesicular nuclei, prominent nucleoli, and mitoses.

Figure 5

Naevoid melanoma from the chest of a young woman. High power views of the dotted area are shown in fig 6.

Figure 6

(A, B) The nuclei appear bland and totally banal. Note, however, the multiple mitoses.

Figure 7

This MIB-1 preparation comes from the dotted areas shown in fig 5.

Figure 8

Atypical Spitz naevus shown at scanning magnification.

Figure 9

(A) Medium power view of fig 8 showing large nests at the deep margin. (B) Multiple mitoses were present at all levels of the naevus.

Figure 10

Dysplastic naevus showing a well developed shoulder on the left side.

Figure 11

(A) Dusty pigment is a typical feature of a dysplastic naevus. (B) Mild cytological atypia showing enlarged hyperchromatic nuclei. (C) Moderate cytological atypia with focal upward migration in a dysplastic naevus. (D) A dysplastic naevus demonstrating severe cytological atypia and prominent nucleoli.

Figure 12

Atypical genital naevus showing papillomatosis and large junctional nests with a distinct retraction artifact.

Figure 13

Atypical genital naevus showing cytological atypia.

Figure 14

Atypical acral naevus showing large expansile oval junctional nests.

Figure 15

Atypical acral naevus. (A) High power view showing retraction artifact. (B) Note the cytological atypia and pagetoid spread.

Figure 16

De novo dysplasia showing atypical epithelioid melanocytes with very occasional suprabasal forms. This is an important precursor lesion and should be fully excised.

Figure 17

Dysplastic naevus showing atypia of junctional and dermal components involving an inked margin.