Neurothekeoma

Nerve Sheath Myxoma

Epidemiology and Etiology:

• Classic nerve sheath myxoma:
• Middle-aged adults (avg 48.4y)
• Cellular neurothekeoma:
• Children and young adults (24y avg)
• F > M
• No association with NF

Common sites:

• Skin
• Face
• Arm
• Shoulder

Gross features:

• 0.5 to 3.0cm
• solitary

Histologic features:

• classic nerve sheath myxoma / mature nerve sheath myxoma:
• sparse neuromesenchymal cells
• variably plump, spindled, slender, elongated with bipolar cytoplasmic extensions, stellate
• interconnecting lobules and fascicles
• no definite direct connection with nerves usually
• abundant myxomatous stroma
• nuclei slightly hyperchromatic without prominent nucleoli
• mitoses sparse or absent
• cellular neurothekeoma / immature nerve sheath myxoma:
• ill-defined, often infiltrative
• may extend to subcutis
• multilobular, fascicular, plexifrom, or nested
• epithelioid cells mainly
• large ovoid nuclei
• ample bright eosinophilic cytoplasm
• indistinct membranes
• chromatin often peripheralized
• prominent nucleolus
• spindle cells also common
• nests or whorls
• plump or ovoid nuclei
• focal myxoid stroma
• may see chronic inflammation, angioplasia, fibrosis, or hyalinization of collagen
• often multiple lines of mesenchymal differentiation:
• neural
• fibrohistiocytic
• myoid
• chondroid
• varying degrees of cytologic atypia
• multinucleated cells may be present
• frequent mitoses
• no definite association with nerve twigs

Immunophenotype:

Marker:	Sensitivity:	Specificity:
NKI-C3
NSE
SMA
S-100 (neg or focal in cellular neurothekeoma) (positive in classic nerve sheath myxoma)
Leu-7

• cellular neurothekeoma has variable and inconsistent immuno pattern – often weak / focal for these markers

Molecular features:

Other features:

References:

• Essentials of AP 2006
• Barnhill 2004