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Skin-Melanocytic Tumors
Last major update: November 2008 - next update November 2009
Revised: 18 September 2009
Author: Nat Pernick, M.D., PathologyOutlines.com, Inc.
Copyright: (c) 2002-2009, PathologyOutlines.com, Inc.
Acral, Ankle, Auricular, Flexicular skin, Genital, Head and neck
Definition
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● Defined as either (a) lesion of volar or dorsal hands/feet or (b) only volar (palm/sole)
Epidemiology
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● Present in 4-9% of population, usually elderly patients
● May resemble early acral melanoma, although melanomas are rare at these sites
● Most common location in Asian patients
Clinical description
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● Circumscribed, light brown, not palpable, flat to side lighting
Dermoscopy
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● Parallel patterns present (Dermatology 2008;216:205)
Dermoscopy images
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Various patterns Transition pattern Various images
Micro description
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● More cellular than most nevi
● Usually junctional; lentiginous pattern common with moderate melanin pigment
● Often low level pagetoid, single cell migration into stratum spinosum
● Possible transepidermal elimination of pigmented nevus cells within stratum granulosum
● Large, oval, vertically oriented junctional nests surrounded by retraction artifact
● Nevus cells mature to lesional base
● Some degree of histologic overlap between acral lentiginous nevi and melanoma
Micro images
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Retraction artifact, cytological atypia and pagetoid spread
Contributed by Angel Fernandez-Flores, MD, PhD, Hospital El Bierzo and Clinica Ponferrada, Spain
Differential Diagnoses
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● Dysplastic nevi - have anastomosing rete ridges, cytological atypia and well-formed lamellar fibroplasia (Histopathology 1995;27:549)
Additional references
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Epidemiology
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● Cases with atypical features typically occur in women (73%)
● Have moderate-severe architectural abnormalities in 100%
● Mild-moderate atypia in 78%, but do not recur (AJSP 2007;31:1130)
Clinical description
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● Often 6 mm or more
● May be symmetric with pagetoid spread and moderate/marked atypia with nucleoli, but no mitotic figures or apoptotic melanocytes (Am J Dermatopathol 2005;27:111)
● May have irregular nesting pattern
● Nests may be poorly circumscribed with lateral extension of junctional component beyond the dermal component
● Also elongation of rete ridges with bridging between them (J Cutan Pathol 2005;32:40)
Sites
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● Axilla, inguinal creases, perianal area, pubis, scrotum, umbilicus
Micro description
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● Lentiginous and nested patterns of junctional proliferation similar to nevi of genital skin
● Confluence of enlarged nests with variation in size, shape and position at dermoepidermal junction
● Diminished cohesion of melanocytes (J Cutan Pathol 2000;27:215)
Differential Diagnoses
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● Dysplastic nevi - cytologic atypia present, stromal alterations
Epidemiology
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● Rare, often large and irregularly shaped
● Usually young women in vulva, also children
Clinical
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● Benign behavior with only rare recurrence (AJSP 2008;32:51)
Atypical melanocytic nevi of genital type:
● Young women, symmetric lesions with well demarcated lateral margins
● Prominent junctional component with round/fusiform nests
● Retraction artifact
● Cellular dyscohesion or single cells
● Mild/moderate atypia
● Benign appearing dermal component with maturation and dense eosinophilic fibrosis in superficial dermis
● No nuclear atypia in superficial dermis, no mitotic figures, does not recur after excision (J Cutan Pathol 2008;35:24)
Micro description
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● Irregular nests and lentiginous melanocytic hyperplasia resembling melanoma, often retraction artifact or cellular dyscohesion
● Mild to severe atypia, but maturation always present
● May have dermal fibrosis
● No/rare mitotic figures
Micro images
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Large expansile oval Papillomatosis and large junctional Atypia is present
junctional nests nests with retraction artifact
Differential Diagnoses
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● Dysplastic nevus - has eosinophilic and lamellar fibroplasia
Clinical description
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● Papular, usually compound nevi in children / young adults
● Evolves into flesh colored dermal nevi with age
Micro description
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● Nevus cells commonly in lower third of reticular nevus
● Scalp nevi often have prominent neural component
Differential Diagnoses
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● Congenital nevus - present at birth, > 1.5 cm, nevus cells within epithelium of skin appendages
End of Skin-Melanocytic Tumors > Nevi – specific sites
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