Soft tissue
Skeletal muscle
Rhabdomyosarcoma, not otherwise specified (NOS)

Author: Nat Pernick, M.D.

Revised: 15 May 2018, last major update July 2009

Copyright: (c) 2002-2018,, Inc.

PubMed Search: Rhabdomyosarcoma not otherwise specified (NOS)

Related Topics: Embryonal rhabdomyosarcoma - general
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Page views in 2019 to date: 106
Cite this page: Pernick, N. Rhabdomyosarcoma, not otherwise specified (NOS). website. Accessed June 25th, 2019.
  • Most common subtype (75%)
  • Mean age 7 years, 2/3 male
  • Usually head and neck, GU, extremities
Clinical features
  • Intermediate prognosis
  • Treatment with multiple agent chemotherapy, surgery and radiation
Gross images

Images hosted on other servers:

Left atrial tumor with hemorrhage and necrosis

Intramuscular white tumor mass

Microscopic (histologic) description
  • Dense zones of undifferentiated, differentiating and well differentiating cells
  • Cells are immediately beneath epithelium (Nicholson cambium layer - resembles hypercellular zones that produce growth rings in trees, see image below)
  • Undifferentiated cells are blue cells with minimal wispy cytoplasm but no skeletal differentiation and central nuclei
  • Differentiating cells have moderate amphophilic or eosinophilic cytoplasm, often fibrillar, may have tadpole shape (tapering bipolar cytoplasm), often with nuclei arranged in tandem
  • Well differentiated cells have cytoplasmic cross striations
  • Matrix is collagenous or myxoid
  • Nuclei usually are dense and smooth with indistinct nucleolus, moderate nuclear pleomorphism but no anaplasia
  • Mitotic figures are associated with less differentiated cells
  • Rarely rhabdoid features (abundant eosinophilic cytoplasm, round / oval cytoplasmic inclusions)
Microscopic (histologic) images

Images hosted on PathOut server:

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

Cells in sheets

Cells in anastomosing fascicles

Individually dispersed cells

Cells in abundant fibromyxoid stroma


Well differentiated
rhabdomyoblasts (found
in 1/3) have eosinophilic
cytoplasm with cross striations


Cells may have abundant
amphophilic or clear cytoplasm,
fine chromatin and small
nucleoli, resembling lymphoma


Cells often have clear
cytoplasm due to glycogen,
rarely causing a spiderweb

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

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)

Desmin: cross striations

Desmin: muscle differentiation in rhabdoid cells

Desmin: spindle cells

Images hosted on other servers:

Nicholson cambium layer


Desmin: reticulin

Cytology description
  • Noncohesive undifferentiated cells with minimal cytoplasm, variable cytoplasm in differentiating cells
  • Cross striations only in well differentiated cells
  • Nuclei are dense with indistinct nucleoli
  • Rarely intranuclear cytoplasmic inclusions (Diagn Cytopathol 2009;37:740)
Cytology images

Images hosted on PathOut server:

Noncohesive, poorly differentiated
cells with no / minimal cytoplasm
or differentiating cells with
variable eosinophilic cytoplasm

Positive stains
Molecular / cytogenetics description
Microscopic (histologic) images

Images hosted on other servers:

Allelic loss of imprinted region at 11p15.5

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