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Nevoid Melanoma
The term nevoid melanoma refers to melanomas, which closely resemble a melanocytic nevus under the microscope. It primarily refers to a diagnostic pitfall. In principle any type of nevus could be mistaken for melanoma, and the term “nevoid” melanomas could therefore include melanomas simulating a Spitz nevus (spitzoid melanoma), blue nevus (blue nevus–like melanoma), deep penetrating nevus (deep penetrating nevus–like melanoma), or other nevi. One may also include lentiginous or nested “nevoid” variants of melanoma in situ with no or minimal pagetosis that are difficult to distinguish from a junctional melanocytic nevus. A more “classic” definition of nevoid melanoma refers to lesions simulating the appearance of a conventional acquired or congenital melanocytic nevus. We recommend the term nevoid melanomas not be used for spitzoid melanomas since there is some evidence that Spitzoid lesions may have a better prognosis.
Clinical Findings
Nevoid melanomas can occur in a broad age range, from children to young or old adults. Sites of involvement are most often areas of intermittently sun-damaged skin followed by areas of chronic sun damage. The clinical appearance ranges from amelanotic pink papules, to brown, gray, or black smooth or papillomatous papules or nodules ( Box 17.1 ). Some lesions are relatively flat. Most often the lesions are clinically felt to be nevi and removed for “irritation” or to “rule out atypia.” Dermoscopic assessment can assist in their diagnosis. In amelanotic lesions, polymorphous vascular patterns often with combinations of dot and linear irregular vessels are a potential diagnostic clue. In pigmented lesions, areas of off-center blue gray veil, chrysalis, streaks, or irregular off-center blotches can raise suspicion for a possible melanoma. With regard to clinical outcome, most of the literature suggests that when nevoid melanomas are compared with similarly staged conventional melanoma, there is no significant difference in prognosis.
Box 17.1
Nevoid Melanoma
Clinical Findings
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Wide age range
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Flat, papular and verrucous/papillomatous lesions
Histopathologic Findings
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Densely cellular melanocyte aggregates filling and expanding papillary dermis
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Long thin elongated rete ridges
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Packed dermal papillae surrounded by bent thin rete ridges (“puffy shirt sign”)
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Nuclear atypia
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Mitoses
Differential Diagnosis
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Mitotically active nevus
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Nevus with unusual features
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