Skin melanocytic tumor

• Melanocytic nevi on the skin of soles and palms, nail matrix or bed, knees and elbows
• Nevi on acral skin are rarely precursors of melanoma (Dermatopathology (Basel) 2022;9:292)

• Relatively frequent lesions occurring in 4 - 9% of Caucasians (Arch Dermatol 2010;146:1085)
• More common in individuals with higher constitutional pigmentation and many melanocytic nevi on the skin
• Different distribution in the world (U.S. > Japan) (J Am Acad Dermatol 2009;60:767)
• F > M (2 - 3:1) (J Am Acad Dermatol 2016;74:724)

• Palms, soles, fingernails > toenails

• Usually small, dark brown or black lesions, with irregular but sharp margins
• Most are flat and rarely (particularly on the volar skin) elevated

• Dermoscopy plays a crucial role in the diagnosis
• Array of thin, parallel dark brown lines (corresponding the acral furrows) in a light brown background (J Dermatol 2011;38:25)
• Maturation with descent of dermal component is the most strong indicative parameter of a benign acral nevus

• Benign; rare progression to melanoma (Dermatology 1993;186:88)

• 4 year old boy with an acral pigmented spitz nevus that clinically mimicked acral lentiginous malignant melanoma (Ann Dermatol 2011;23:246)
• 23 year old woman with a Spitz nevus on acral volar skin (Indian J Dermatol Venereol Leprol 2019;85:629)
• 37 year old pregnant woman with acral superficial spreading melanoma arising on melanocytic nevus of the left palm (Indian J Dermatol 2015;60:609)

• Excision

Contributed by Lucia Lospalluti, M.D.


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• About half of the cases are typical and without any peculiar aspects (so called typical features)
• May be junctional, compound or intradermal
• Small nests of epithelioid cells with inconspicuous nuclei at the junction and small, round melanocytes in the dermis
• Atypical cells are possible (sometimes with large vesicular or hyperchromatic nuclei) but they are only occasional, scattered among typical, innocent looking melanocytes
• Lentiginous junctional pattern is more common than in nevi of nonacral sites (so called acral nevi with atypical features) with spare of the crista profunda intermedia (prominent melanocytic hyperplasia worrisome for Acral Melanoma in situ)
• Often (61%) low level pagetoid, single cell migration into stratum spinosum, summarized by the acronym MANIAC (melanocytic acral nevus with intraepithelial ascent of cells) (Am J Surg Pathol 1995;19:792, Am J Dermatopathol 2000;22:556)
• Pagetoid cells should not be atypical and should not be present beyond the center of the lesion
• Possible columns of pigment present in the cornified layer, among the corneocytes
• Nevus cells mature to lesional base
• May have architectural disorder with moderately large melanocytes, bridging fibroplasia (so called special site features) (J Cutan Pathol 2008;35:889)
• Usually lesions do not seem well circumscribed (this phenomenon can also depend on the plane of the section)

Contributed by Gerardo Cazzato, M.D. and Angel Fernandez-Flores, M.D., Ph.D.

What is the most important clinical aid in the dermatopathological diagnosis of an acral nevus?

1. Asymmetry
2. Borders
3. Color
4. Dermoscopy
5. Time of onset

D. Dermoscopy is the most important clinical feature to help the dermatopathological diagnosis of acral nevi. A pattern with an array of thin, parallel, dark brown lines (corresponding to the acral furrows) in a light brown background are characteristic of the lesion. Asymmetry (answer A), borders (answer B), color (answer C) and time of onset (answer E) are also important but in the second instance.

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Reference: Acral nevus

In an acral nevus showing lively junctional activity, what is the diagnostic clue of benignity of the lesion?

1. Asymmetry
2. Localization
3. Maturation with descent of dermal component
4. Small nests of melanocytes at the junction
5. Time of onset

C. Maturation with descent of dermal component is the most histological parameter for the benignity of the lesion. Asymmetry (answer A) is a possibility for an acral nevus. Localization (answer B) is obvious but not an indicator of malignancy. Small nests of melanocytes at the junction (answer D) and time of onset (answer E) are common in an acral nevus without signs of malignancy.

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Reference: Acral nevus