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Soft tissue
Skeletal muscle
Embryonal rhabdomyosarcoma not otherwise specified (NOS)

Reviewer: Nat Pernick, M.D. (see Reviewers page)
Revised: 6 December 2013, last major update July 2009
Copyright: (c) 2002-2013, PathologyOutlines.com, Inc.

Epidemiology
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Clinical features
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Gross images
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Left atrial tumor with hemorrhage and necrosis
Intramuscular white tumor mass
Micro description
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Micro images
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Most tumors contain undifferentiated round or oval cells with sparse clear or amphophilic wispy cytoplasm, dense chromatin and irregular nuclear membranes
Diagnostic cells have increased eosinophilic or basophilic cytoplasm that displace the dense hyperchromatic nucleus
Paucicellular tumor due to markedly edematous or myxoid stroma
Dense condensations of rhabdomyoblasts
Cells in sheets
Cells in anastomosing fascicles
Individually dispersed cells
Cells in abundant fibromyxoid stroma
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Fig 1: well differentiated rhabdomyoblasts (found in 1/3) have eosinophilic cytoplasm with cross striations
Fig 2: cells may have abundant amphophilic or clear cytoplasm, fine chromatin and small nucleoli, resembling lymphoma
Fig 3: cells often have clear cytoplasm due to glycogen, rarely causing a spiderweb appearance
Figs 4, 5, & 6: Differentiating cells have tapered, bipolar cytoplasm or a tadpole shape with the nuclei at one end; nuclei may be arranged in tandem (like cars on a train)

Nicholson's cambium layer
Nuclei are small with pleomorphism
Tumors rarely consist primarily of cells with circumscribed, pink, ground glass or fibrillar cytoplasmic inclusions but no cross striations, nuclei may be more vesicular than usual with prominent nucleoli
Myogenin
Desmin: cross striations
Desmin: muscle differentiation in rhabdoid cells
Desmin: spindle cells
Desmin: reticulin
Cytology description
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Cytology images
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Noncohesive, poorly differentiated cells with no/minimal cytoplasm
or differentiating cells with variable eosinophilic cytoplasm
Positive stains
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Molecular / cytogenetics description
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Molecular / cytogenetics images
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Allelic loss of imprinted region at 11p15.5
End of Soft tissue > Skeletal muscle > Embryonal rhabdomyosarcoma not otherwise specified (NOS)


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