• Superficial tumor, first described in 1980
  
• Originally, derivation thought to be from nerve sheath; now thought to derive from fibroblasts with ability to differentiate into myofibroblasts and to recruit histiocytes (Am J Surg Pathol 2007;31:1103)

• Usually head, upper extremities or shoulder girdle

• Solitary, superficial, slow growing mass up to 2 cm
• 60% women, mean age 17 years (range 2-85 years), 80% are < age 30 at initial diagnosis

• 5 month old boy with thumb swelling (Indian J Dermatol 2009;54:59)
• 19 year old woman with painful subcutaneous nodule on lower back (Dermatol Online J 2009;15:3)
• 66 year old man with painless swelling in eyelid (Indian J Ophthalmol 2008;56:334)

• Excision, may recur

Thumb nodule

Lower back

Lower eyelid

• Cellular, myxoid or mixed subtypes
• Involves dermis or subcutis
• Multinodular mass with myxoid matrix and peripheral fibrosis
• Whorled or focally fascicular patterns of spindled and epithelioid mononuclear cells with abundant cytoplasm, indistinct cell borders
• Margins usually positive; usually occasional multinucleated giant cells
• Variable nuclear atypia
• Median 4 MF/25 HPF, may have 10+ MF/25 HPF, may be atypical

Left thumb nodule of 5 month old boy

Lower eyelid of elderly man

Lobular proliferation with myxoid stroma

Mucin deposits (Alcian blue)

S100

• Vimentin, NKI/C3, CD10, MiTF

• S100, GFAP, MelanA

• Nerve sheath myxoma

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