Vulva, vagina & female urethra
Melanocytic lesions
Atypical melanocytic nevi of the genital type
Last author update: 1 July 2016
Last staff update: 7 September 2023 (update in progress)
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PubMed Search: Atypical melanocytic nevi of genital type
Table of Contents
Essential features | Terminology | Epidemiology | Sites | Clinical features | Treatment | Clinical images | Gross description | Microscopic (histologic) description | Microscopic (histologic) images | Molecular / cytogenetics description | Differential diagnosis | Additional referencesCite this page: Strickland S. Atypical melanocytic nevi of the genital type. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/vulvaAMNGT.html. Accessed September 26th, 2023.
Essential features
- Considered a nevus of special site
- Atypical histologic features but benign behavior
Terminology
- Nevus of milk line type (Arch Pathol Lab Med 2003;127:e391)
Epidemiology
- Vulva of young women: age range 6 - 54 years, median 26 years (Am J Surg Pathol 2008;32:51)
Sites
- Most commonly on labia majora, labia minora and clitoris
- Also mons pubis and perineum
- Hair bearing skin or mucosa
- Occurs rarely on male genitalia
Clinical features
- Usually does not recur following excision; only one case of local recurrence reported (Am J Surg Pathol 2008;32:51)
- No documented metastases
Treatment
- Local excision
Clinical images
Images hosted on other servers:
Figure 3: Irregular dots on the periphery of the lesion
Figure 1: Photomicrograph of pigmented lesion
Gross description
- 1.3 - 20 mm in size (mean 5 - 7 mm) (Am J Surg Pathol 2008;32:51, Hum Pathol 1998;29:S1, J Invest Dermatol 2016;136:1858)
- Raised or flat in appearance
- Tan / brown but may have some black areas (Hum Pathol 1998;29:S1)
- Rarely ulcerated
Microscopic (histologic) description
- Three histologic patterns originally described: (Hum Pathol 1998;29:S1)
- Nested pattern - a predominance of variably sized but typically large, often oval nests, oriented perpendicular or parallel to the dermal-epidermal junction
- Dyshesive nested pattern - nearly contiguous dyshesive nests forming a band that separates the epidermis from the mature dermal melanocytes
- Crowded pattern - closely apposed ill defined nests and single cells obscuring the dermal epidermal junction
- Junctional melanocytic proliferation composed of large, variably sized nests with prominent retraction artifact or cellular dyscohesion
- Nests may be perpendicular or parallel to epidermal surface
- Melanocytic cytologic atypia ranging from mild to severe
- Focal pagetoid spread, most often centrally located
- Common to see focal lentiginous melanocyte proliferation
- Large underlying "mushroom shaped" dermal component with maturation
- Adnexal involvement in up to 46%
- Dermal mitoses uncommon but may be present: up to two per tissue section
- Lymphocytic infiltrate inconspicuous
- May see giant cells
- Coarse melanin pigment and melanin incontinence
- Nondescript stromal pattern / stromal fibrosis
Microscopic (histologic) images
Contributed by Priya Nagarajan, M.D., Ph.D.
Dysplastic nevus with mild atypia
Dysplastic nevus with moderate atypia
Dysplastic nevus with moderate atypia
Dysplastic nevus with severe atypia
Mucosal melanotic macule
Images hosted on other servers:
Melanocytic nests are
well delineated; arranged
as oval and somewhat
irregular masses
Large and uniform cells with prominent nucleoli
Nests of nevus cells arranged in a form known as "jigsaw puzzle"
Figures 1 - 4: Atypical genital nevus
Molecular / cytogenetics description
- BRAF V600E mutations in 23% and 72% of cases (Br J Dermatol 2010;162:677, J Invest Dermatol 2016;136:1858)
- Nonoverlapping pattern of oncogenic mutations compared to vulvovaginal melanomas (J Invest Dermatol 2016;136:1858)
Differential diagnosis
- Dysplastic nevus (DN):
- More pronounced lentiginous proliferation of single cells
- Smaller nests along elongated rete ridges
- More pronounced shoulder component
- Contains eosinophilic fibroplasia and lamellar fibroplasia (whereas atypical melanocytic nevus of genital type most often has a nondescript pattern of dermal fibrosis)
- Increased lymphocytic infiltrate and vascular ectasia
- Melanoma:
- Primarily postmenopausal women
- Lacks symmetry
- Lacks maturation
- Greater cytologic atypia
- Increased dermal mitoses/atypical mitoses
- Pagetoid spread of melanocytes more pronounced
- Plaque-like lymphocytic infiltrate (if radial phase melanoma)
- Diffuse eosinophilic fibrosis with angiogenesis
