Histologic mimics of malignant melanoma

Abstract

Although spongiotic (eczematous), psoriatic and cutaneous skin infections are among the most common in dermatology consultations, melanocytic lesions - including the different types of nevi and melanomas - are among those that cause a great deal of concern and stress to patients and their clinicians. A diagnosis of benign melanocytic nevus carries a very good prognosis. However, a diagnosis of melanoma might indicate more aggressive treatment, lifelong surveillance and a worse prognosis. Differentiating between these conditions is not always a straightforward process for clinicians and pathologists. Therefore, knowledge of melanoma mimickers is very important for clinicians in general, and dermatologists and pathologists in particular. In this review, we called attention to some of the more frequent benign but unusual melanocytic lesions that are of diagnostic concern for clinicians evaluating these cutaneous proliferations.

Keywords: deep penetrating nevus; dysplastic nevus; melanocytic lesions; melanoma; pigmented spindle cell nevus.

Fig. 1

Photomicrograph of dysplastic nevus shows fusion of the adjacent rete ridges (white arrow) and subepidermal eosinophilic lamellar fibroplasia (black arrow) (Haematoxylin & eosin, × 100).

Fig. 2

Photomicrograph of Spitz nevus shows predominantly epithelioid melanocytes at the dermal-epidermal junction, artifactual clefting surrounding nests and maturity with depth (Haematoxylin & eosin, × 100).

Fig. 3

Photomicrograph of pigmented spindle cell nevus shows mainly junctional, uniform and heavily pigmented melanocytes with dermal inflammation (Haematoxylin & eosin, × 40).

Fig. 4

Photomicrograph of cellular blue nevus shows nested and relatively uniform oval melanocytes admixed with heavily pigmented dendritic cells and melanophages. Thickened and trapped collagen bundles are also identified between the nests (Haematoxylin & eosin, × 200).

Fig. 5

Photomicrographs of deep penetrating nevus show (a) dermally located nevus penetrating around a hair follicle without destructing it; (b) the characteristic deep penetration with pushing borders (Haematoxylin & eosin, × 40).

Fig. 6

Photomicrograph of acral nevus shows junctional melanocytic nests and the characteristic hyperkeratosis seen at these sites (Haematoxylin & eosin, × 100).

Box 1

Acral nevus vs. acral lentiginous melanoma:

Fig. 7

Photomicrograph of recurrent nevus shows single junctional melanocytes and dermal melanophages overlying a dermal scar with vertically oriented vessels (black arrows) (Haematoxylin & eosin, × 100).