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Soft Tissue Tumors Part 3 - Muscle, Vascular, Nerve, Other
Neuromuscular hamartoma
Author: Nat Pernick, M.D, PathologyOutlines.com, Inc.
Revised: 17 July 2009, last major update July 2009
Copyright: (c) 2002-2009, PathologyOutlines.com, Inc.
Definition
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● Rare developmental lesion of mature skeletal muscle and nerve
Terminology
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● Not a WHO diagnosis
● Also called benign Triton tumor (malignant Triton tumor refers to rhabdomyosarcoma plus MPNST), neuromuscular choristoma
Epidemiology
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● Usually < 2 years old, affects brachial plexus or sciatic nerve
Case reports
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● 15 year old boy with tumor of trigeminal nerve (AJNR Am J Neuroradiol 2005;26:967)
● 36 year old woman with tumor of trigeminal nerve (Acta Neurochir (Wien) 2006;148:83)
Treatment and prognosis
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● Biopsy for diagnosis plus observation, may develop fibromatosis after biopsy or complete excision
Gross description
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● Circumscribed, firm, gray-brown-white, multinodular, attached to nerve
Micro description
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● Multiple nodules, each 3-5 mm, separated by narrow bands of connective tissue
● Nodules are composed of fascicles of striated muscle of varying size with nerve fibers (myelinated or not) within same perimysial fibrous sheath
● Stroma may be more cellular with bland spindle cells and resemble fibromatosis
Micro images
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AFIP images
Nodules of skeletal muscle and neural Nodules contain fascicles of striated muscle
elements that subdivide into smaller nodules fibers of variable size and nerve fibers (with
by narrow bands of connective tissue or without myelination) in same perimysial
fibrous sheath
Rare case with haphazardly distributed skeletal muscle and nerve fibers, cellular stroma and bland spindle cells with scant cytoplasm and oval nuclei
Nerve fibers are S100+
Positive stains
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● Striated muscle - desmin and muscle specific actin
● Nerve - S100
Differential Diagnoses
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● Fetal rhabdomyoma - usually not intimately associated with nerves, S100 negative
● Embryonal rhabdomyosarcoma - poorly and moderately differentiated cells
End of Soft Tissue Tumors Part 3 - Muscle, Vascular, Nerve, Other > Neuromuscular hamartoma
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