Overcalling of Genital Nevi as Melanomas.

Atypical Genital Nevi
Awareness of a unique subtype of pigmented vulvar lesion will prevent misdiagnosis of melanoma.
Gleason BC et al. Atypical genital nevi. A clinicopathologic analysis of 56 cases. Am J Surg Pathol 2008 Jan; 32:51.

The incidence of pigmented lesions and diffuse hyperpigmentation involving the genitalia is difficult to ascertain, but such lesions can be found in about 10% of white women. Approximately 2% of these are nevocellular nevi (other benign pigmented lesions found here include seborrheic keratoses, melanoses, lentigines, warts, and postinflammatory hyperpigmentation). In general, nevi on the vulva are identical in morphology and histopathology to nevi elsewhere on the body, except for a small subset of nevi in younger women that have the unusual feature of enlarged junctional nests varying in size, shape, and position. Their long-term biologic behavior has not been determined. The histologic and clinical features of these "atypical melanocytic nevi of the genital type" or "atypical genital nevi" (AGN) are the subject of this study.
The authors reviewed hematoxylin- and eosin-stained sections and medical records from 56 cases of AGN. Mean patient age was 26, but four patients were younger than 10 years. Nearly half the lesions were atypical on clinical exam (mean diameter, 6 mm). More than half arose in hair-bearing skin, the rest in glabrous skin or mucosa. In the pediatric group, juxtamucosal or glabrous surfaces (clitoris and labium minus) were the most frequently affected.

The mean follow-up period was 3.5 years. Ten of 17 cases with positive margins had follow-up data available; only 1 of these persisted or recurred, with no further recurrence after complete excision. About 80% of lesions were compound; more than two thirds showed moderate-to-severe cytologic atypia. Ten cases were focal but had pagetoid spread. Adnexal spread and nuclear atypia of the melanocytes situated in the superficial dermis were relatively common. Rare mitoses were identified (maximum, 2 per section). Dermal fibrosis was seen in 45%.

Comment: Melanocytic lesions in the genitalia and along the milk line (axillae, breasts, periumbilical region, and groin) have a tendency to be overdiagnosed as malignant melanomas, a pitfall ascribable to the presence of histologic features usually associated with aggressive biologic behavior. Awareness of this distinct subgroup of pigmented lesions affecting women of reproductive age is essential to avoid unnecessary surgery and patient distress. Although follow-up data on these lesions are limited, among 63 cases in the literature, no metastases have been reported to date.