Soft tissue

Skeletal muscle


Last author update: 1 December 2017
Last staff update: 25 July 2023

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PubMed Search: Ectomesenchymoma

Kenneth A. Iczkowski, M.D.
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Cite this page: Iczkowski KA. Ectomesenchymoma. website. Accessed November 29th, 2023.
Definition / general
  • Ectomesenchymoma is a rare, fast growing tumor of the nervous system or soft tissue that occurs mainly in children
Essential features
  • Sites described most often include head / neck, abdomen, perineum, scrotum and limbs
Clinical features
  • Fast growing tumors that eventually cause pain
Radiology description
  • CT scan may show anterior displacement of bladder and rectal compression
Prognostic factors
  • Stage and size < 10 cm
Case reports
  • 5 month old boy with a 7.5 cm mass emanating from the prostate (Pediatr Surg Int 1999;15:68)
    • Tumor was resected and after a course of chemotherapy, recurred 8 months later, causing fatal intestinal obstruction
    • This is the only case report of ectomesenchymoma of the prostate
  • Surgery and chemotherapy have been described; prognosis is guarded
Gross description
  • Rubbery, white
Microscopic (histologic) description
  • 2 histologic components:
    • Skeletal muscle component: round to oval cells with abundant glycogenated cytoplasm and cross striations
    • Component analogous to ganglioneuroma: hypocellular area of spindle cells with wavy nuclei and long eosinophilic cytoplasmic processes; admixed ganglion cells
Microscopic (histologic) images

Contributed by Brendan C. Dickson, M.D., M.Sc.

Spindle cells and neuronal elements

Rhabdomyoblastic differentiation and mitoses



Images hosted on other servers:

Male infants with pelvic / urogenital tumors

34 year old man with paratesticular tumor

Positive stains
Negative stains
Molecular / cytogenetics description
Differential diagnosis
Board review style question #1
Which of the following is true of ectomesenchymoma of the prostate?

  1. It has 3 histologic components
  2. It is S100 positive in the neural component
  3. It is a slow growing tumor
  4. It should be cytokeratin positive
  5. It should be negative for desmin
Board review style answer #1
B. It is S100 positive in the neural component

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Reference: Ectomesenchymoma
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