Soft tissue
Skeletal muscle
Neuromuscular hamartoma

Topic Completed: 1 November 2012

Minor changes: 29 September 2020

Copyright: 2002-2020,, Inc.

PubMed Search: Neuromuscular hamartoma

Vijay Shankar, M.D.
Page views in 2019: 1,068
Page views in 2020 to date: 981
Cite this page: Shankar V. Neuromuscular hamartoma. website. Accessed November 30th, 2020.
Definition / general
  • Rare developmental lesion of mature skeletal muscle and nerve
  • Not a WHO diagnosis
  • Also called benign triton tumor (malignant triton tumor refers to rhabdomyosarcoma plus MPNST), neuromuscular choristoma
Clinical features
  • Usually < 2 years old, affects brachial plexus or sciatic nerve
  • May involve large cranial nerve trunks and present as intracranial mass
  • Very rarely involves peripheral nerve and presents as small nodules
  • Aggressive behavior
Case reports
  • Biopsy for diagnosis plus observation, may develop fibromatosis after biopsy or complete excision
  • May recur, mandating regular followup after excision
Gross description
  • Circumscribed, firm, gray-brown-white, multinodular, attached to nerve
Microscopic (histologic) description
  • 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
Microscopic (histologic) images

AFIP images

Nodules of skeletal muscle and neural elements that subdivide
into smaller nodules by narrow bands of connective tissue

Nodules contain fascicles of striated muscle fibers of variable size and
nerve fibers (with 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
Differential diagnosis
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