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Soft Tissue Tumors Part 3 - Muscle, Vascular, Nerve, Other
Spindle cell variant of embryonal rhabdomyosarcoma
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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● Highly differentiated form of embryonal rhabdomyosarcoma composed of 50%+ elongated spindle cells, and associated with a good prognosis
Epidemiology
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● First described in 1992; usually boys in paratesticular, head or neck regions (Am J Surg Pathol 1992;16:229) or adults in non-paratesticular regions (Am J Surg Pathol 2005:29:1106, Virchows Arch 2006;449:554)
● 6% of embryonal rhabdomyosarcoma
Case reports
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● 15 year old boy with paratesticular mass (Case of Week #145)
● Cardiac tumor (Pathol Res Pract 2009 Jul 2 [Epub ahead of print])
Treatment and prognosis
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● Favorable prognosis in children after excision, more aggressive in adults (Amer J Surg Pathol 2005;29:1106)
Gross description
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● Firm, fibrous tumor with tan-yellow, whorled cut surface resembling leiomyoma
Micro description
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● 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
Micro images
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Relatively differentiated spindle cells 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
15 year old boy with paratesticular mass (Case of Week #145)
Myogenin Desmin Smooth muscle actin AE1/AE3
Bladder tumor
Desmin+ rhabdomyoblasts are usually present,
but often sparse
Cytology description
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● Numerous spindle cells and large fragments of cytoplasmic processes with cross-striations (Acta Cytol 2005;49:331)
Positive stains
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● Desmin, myogenin, muscle specific actin, smooth muscle actin, vimentin (Arch Pathol Lab Med 2006;130:1454)
● Also titin (marker of terminal differentiation)
Negative stains
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● Caldesmon, S100, PLAP, AE1/AE3, CD117 (Zhonghua Zhong Liu Za Zhi 2008;30:141)
Differential Diagnoses
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● Fibrosarcoma - herringbone pattern, may have similar morphology but no rhabdomyoblasts, negative for skeletal muscle markers
● Leiomyosarcoma - usually high grade with mitotic figures or necrosis
● 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
End of Soft Tissue Tumors Part 3 - Muscle, Vascular, Nerve, Other > Spindle-cell variant of embryonal rhabdomyosarcoma
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