Soft tissue
Skeletal muscle
Spindle cell variant of embryonal rhabdomyosarcoma

Author: Nat Pernick, M.D.

Revised: 31 January 2018, last major update July 2009

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

PubMed Search: Spindle cell variant of embryonal rhabdomyosarcoma

Related topics: Embryonal rhabdomyosarcoma - general

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Cite this page: Pernick, N. Spindle cell variant of embryonal rhabdomyosarcoma. website. Accessed June 25th, 2019.
Definition / general
  • Highly differentiated form of embryonal rhabdomyosarcoma composed of 50%+ elongated spindle cells and associated with a good prognosis
Case reports
Prognosis and treatment
Gross description
  • Firm, fibrous tumor with tanish yellow, whorled cut surface resembling leiomyoma
Microscopic (histologic) description
  • 50% of more of tumor cells should be spindled for this diagnosis
  • Low grade, fascicular or storiform pattern of uniform, relatively differentiated elongated spindle cells
  • Scattered spindled or polygonal rhabdomyoblasts with brightly eosinophilic cytoplasm and pleomorphic nuclei are also present
  • Cytologic features similar to smooth muscle tumors with blunted central nuclei and tapered ends but with pale indistinct cytoplasm
  • Cross striations are rare
  • Low mitotic activity
Microscopic (histologic) images

Images hosted on PathOut server:

Spindle cells resemble leiomyosarcoma

Spindle cells resemble MFH

Somewhat bland spindle cells are characteristic


May be paucicellular with fibrotic stroma
containing undifferentiated round and spindle
cells mixed with differentiating rhabdomyoblasts
with abundant eosinophilic cytoplasm


Desmin+ rhabdomyoblasts
are usually present
but often sparse

15 year old boy with paratesticular mass (Case of Week #145):



Smooth muscle actin

AE1 / AE3

Images hosted on other servers:

Bladder tumor

Cytology description
  • Numerous spindle cells and large fragments of cytoplasmic processes with cross striations (Acta Cytol 2005;49:331)
Positive stains
Differential diagnosis
  • Fibrosarcoma: herringbone pattern, may have similar morphology but no rhabdomyoblasts, negative for skeletal muscle markers
  • Infantile fibromatosis: deep location, fascicles of spindle cells, no cross striations, no undifferentiated cells
  • Leiomyosarcoma: usually high grade, cigar shaped nuclei, mitotic figures and necrosis, no rhabdomyoblasts, often positive for caldesmon, negative for myoglobin
  • Neuromuscular hamartoma of soft tissue: usually age < 2 years, affects brachial plexus or sciatic nerve, multinodular growth with connective tissue separating nodules, no rhabdomyoblasts, muscular component is positive for desmin and muscle specific actin, neural component is positive for S100
  • Rhabdomyoma: benign tumor of skeletal muscle differentiation, no rhabdomyoblasts, no pleomorphism, no necrosis
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