Dermatology Online Journal

Atypical melanocytic nevi of genital type: A distinctive pigmented lesion of the genital tract often confused with malignant melanoma
M Ruhul Quddus MD¹, Lanita B Rashid BS¹, C James Sung MD¹, Leslie Robinson-Bostom MD², W Dwayne Lawrence MD¹
Dermatology Online Journal 16 (2): 9

1. Departments of Pathology, Women & Infants Hospital, The Alpert Medical School of Brown University, Providence, Rhode Island. mquddus@wihri.org
2. Rhode Island Hospital, The Alpert Medical School of Brown University, Providence, Rhode Island

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Abstract

A 30-year-old female presented with a 0.3 cm slightly raised tan-brown papule with somewhat irregular borders on her right labia minora. The papule was detected by her gynecologist during an annual gynecologic visit. Excision of the lesion revealed an atypical melanocytic nevus of genital type (AMNGT). This nevus is often confused with other pigmented lesions especially dysplastic nevus or even malignant melanoma. This distinctive melanocytic nevus often causes significant concern to pathologists and dermatologists. The diagnostic criteria and differentiating features from dysplastic nevi and malignant melanoma are discussed.

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Background

Pigmented lesions of the genital area often pose a significant diagnostic challenge.

The malignant potential of melanocytic lesions of the vulva are well described in the literature [1, 2, 3]. However, there are no specific genital melanocytic lesions identified that serve as possible precursors to malignant melanoma [4]. In general, dysplastic nevi and malignant melanoma are rare in the genital areas. However, when present, it is important to differentiate these entities from other benign pigmented lesions. A number of epidemiologic studies have shown that dysplastic nevi can be precursors to the development of malignant melanoma [5, 6, 7].

In recent years, AMNGT occurring in young women has come to be regarded as a relatively distinct clinicopathologic entity that must be distinguished from vulvar malignant melanoma. Indeed, the diagnosis of malignant melanoma is either rendered or seriously considered either by pathologists and dermatologists in these cases. A recent study by Stern and Haupt [8] found that as high as 80 percent of vulvar nevi showed pagetoid melanocytosis in the epidermis. This finding reconfirms that both the macroscopic and microscopic features of atypical genital nevi may create confusion with malignant melanoma, particularly since atypical genital nevi are often sent to the pathologists with the clinical diagnosis of “rule out malignant melanoma.” So a correct diagnosis is important to avoid radical surgical procedures in these young women.

Atypical melanocytic nevus of genital type is usually asymptomatic and often first discovered during pregnancy. We present an incidentally detected AMNGT and discuss the diagnostic features of this distinctive but difficult lesion.

Case Report

Figure 1
Figure 1. Photomicrograph of an incidentally detected pigmented lesion near the distal third of the labia minora of a 30-year-old female

The patient is a 30-year-old white female who presented to her gynecologist for an annual check up. The gynecologist noticed an asymptomatic, slightly raised, evenly pigmented tan-brown, symmetrical papule with somewhat irregular borders on her right labia minora towards the distal third of the vulva. The patient had not noticed the lesion before, so its duration could not be ascertained. A photograph of a similar lesion is depicted in Figure 1.

The patient had no other significant medical problems. The lesion was excised and the specimen was processed for routine histopathologic examination.

Gross Description

The specimen consisted of an excisional biopsy of skin measuring 0.3 x 0.2 x 0.2 cm in maximum dimension. The skin surface revealed a slightly raised, evenly pigmented, 2.5 mm, tan brown papule with somewhat irregular borders. The surgical margins appeared free from the pigmented area. No ulcer was noted. The lateral and deep surgical margins were inked and the specimen was submitted entirely for microscopic examination.

Microscopic Examination

Figure 2	Figure 3a
Figure 2. Melanocytic nests are well delineated and arranged as oval and somewhat irregular masses. The long axis of these nests is parallel to the epidermal surface (H&E, x4). Figure 3a. The cells are large and uniform with prominent nucleoli and pigmentation with large course melanin granules. Crowding of melanocytes is seen at the DEI and differentiated cells extend into the deep dermis (H&E, x40).

Figure 3b
Figure 3b. Nests of nevus cells are arranged in a form what has been described as “jigsaw puzzle” (H&E, x10).

Multiple levels of H&E stained sections were examined and these revealed a small well-circumscribed melanocytic tumor characterized by irregular, confluent, crowded and dyscohesive nests of melanocytes at the dermo-epidermal interface (DEI). The melanocytic nests are well delineated and arranged as oval and somewhat irregular masses. The long axis of these nests are parallel to the epidermal surface (Figure 2). The cells are large and uniform with prominent nucleoli and pigmentation with large course melanin granules. Crowding of melanocytes is seen at the DEI and differentiated cells extend into the deep dermis (Figure 3a). In some areas, the nests of nevus cells are arranged in a form what has been described as “jigsaw puzzle” (Figure 3b). The cells in the deeper nests are non-pigmented. Patchy dense lymphocyte infiltrate is present in and around the lesion. These pathologic features are characteristic of the AMNGT.

Conclusion

Atypical melanocytic nevi of genital type usually present as an asymptomatic lesion and are discovered incidentally during routine physical examination or self-examination [9]. The median age of presentation of this lesion is 23 years; however, it can occur in children and teens. The size varies from 1.3 mm to 18 mm with a mean diameter of 5.9 mm.

Despite its atypical histologic appearance, lesions that have been followed for as long as 15 years have shown no evidence of malignant transformation [9]. Therefore, it has been suggested that the lesions are stable despite their atypical histologic features. It should, however, be emphasized that its possible progression to malignancy must be carefully evaluated. Atypical melanocytic nevi of genital type may present as a macule or papule. The macules on the labia minora and clitoris are often black and may raise the concern of a melanoma, which is further complicated by the presence of cytologic atypia on histologic examination. The distinctive pathologic features are present at the dermo-epidermal interface (DEI), careful evaluation of the DEI and other typical features usually clinch the diagnosis. The stromal features which distinguish AMNGT from dysplastic nevi and melanoma are the following: concentric eosinophilic fibroplasia and lamellar fibroplasia are common in dysplastic nevi; fibroplasia with a plaque-like lymphocytic infiltrate and diffuse eosinophilic fibroplasia are seen in radial growth phase melanoma; a nonspecific stromal pattern is usually noted in AMNGT [9, 10].

Atypical melanocytic nevi of genital type is usually found in the vulva and perineum. However, similar lesions have also been described in the axilla and, uncommonly, in male genitalia [9]. Atypical melanocytic nevi of genital type is more common in the labia minora, whereas dysplastic nevi are more common in the region of labia majora [9].

Although atypical melanocytes are present in these lesions, recurrence or metastasis has not been reported in AMNGT.

References

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