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Soft Tissue Tumors Part 3 - Muscle, Vascular, Nerve, Other
Myxoma of soft tissue
Author: Nat Pernick, M.D, PathologyOutlines.com, Inc.
Revised: 18 July 2009, last major update July 2009
Copyright: (c) 2002-2009, PathologyOutlines.com, Inc.
Definition
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● Gelatinous lesion often deep within muscle of extremity
● Avascular with occasional stellate cells in slightly basophilic matrix
● Not a WHO diagnosis
Clinical
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● May derive from modified fibroblasts
● Usually adults ages 40-70 years
● Sites: thigh, shoulder, upper arm
● May be associated with fibrous dysplasia (both together are termed Mazabraud's syndrome, Ophanet 2005, Pathol Oncol Res 2004;10:121, Am J Surg Pathol 1998;22:1222)
● Cardiac myxoma contains endothelial cells in fibromyxoid matrix, is associated with Carney syndrome, and is considered a separate entity
Case reports
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● 48 year old woman with thigh mass (University of Oklahoma Health Sciences Center)
Treatment and prognosis
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● Excision; rarely recurs if adequately excised
● Cellular cases appear to have same indolent behavior if completely excised (Histopathology 2001;39:287)
Gross description
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● Extremely gelatinous
● Often circumscribed
● Deep within muscle
● May be up to 13 cm
Gross images
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Intramuscular Jaw Gluteal tumor
Images: intramuscular myxoma #1; #2
Micro description
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● Slightly basophilic matrix with usually a few spindle cells at high power with oval nuclei
● Slightly more cellular with collagenized capsule at periphery
● May have areas of increased vascularity or cellularity
● May have central mucinous cyst
● At periphery, may infiltrate striated muscle and be associated with muscle atrophy
Micro images
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Hypocellular tumor Cellular tumor
Intramuscular tumor of forearm Intramuscular tumors
Jaw tumor: bland stellate cells in myxoid stroma
Mandibular myxoma Maxillary tumor
Site unknown
Cytology description
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● Viscous, gelatinous quality when expressed onto glass slide
● Paucicellular, often finely granular myxoid stroma with few cells, usually macrophages or bland spindle cells (Am J Clin Pathol 2005;123:858)
Positive stains
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● Spindle cells - vimentin, CD34 (50%), mucoid matrix - Alcian blue, mucicarmine, colloidal iron
Negative stains
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● S100, desmin
EM images
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Conjunctival myxoma: cell has infolding of nuclear membrane, forming membrane bound vacuoles (v); nuclei has 2 nucleoli; prominent rough endoplasmic reticulum is in lower left; inset-membranous vacuole
Molecular / cytogenetics
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● GNAS1 mutations in 61% of intramuscular myxomas (Mod Pathol 2009;22:718)
● No cytogenetic aberrations
Differential diagnosis
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● Nerve sheath myxoma - periphery has parallel rows of spindle cells with wavy nuclei representing the nerve
● Low grade myxofibrosarcoma - has typical MFH areas, curvilinear vessels (thick walled with broad arc) with condensation of cells around vessels; variable, non-specific cytogenetic aberrations (83%), no GNAS1 activating mutations (J Cell Mol Med 2009 Mar 13 [Epub ahead of print])
References
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End of Soft Tissue Tumors Part 3 - Muscle, Vascular, Nerve, Other > Myxoma
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