Mesenchymal tumors

Reactive nodular fibrous pseudotumor

Topic Completed: 17 February 2021

Minor changes: 3 March 2021

Copyright: 2003-2021,, Inc.

PubMed Search: reactive nodular fibrous pseudotumor

Raul S. Gonzalez, M.D.
Page views in 2020: 2,084
Page views in 2021 to date: 2,067
Cite this page: Gonzalez RS. Reactive nodular fibrous pseudotumor. website. Accessed October 28th, 2021.
Definition / general
Essential features
  • Benign fibroinflammatory mass more common in men
  • Stains for AE1 / AE3, CD117 and muscle specific actin
  • Does not appear to recur
  • Usually arises in mesentery; may involve colon or small bowel
Clinical features
  • Usually occurs in patients aged 40 - 60; more common in men
  • Associated with prior abdominal surgery
  • Can cause acute abdominal pain but sometimes discovered incidentally
Case reports
  • Complete resection appears curative
Clinical images

Images hosted on other servers:

Protruding lesion on back wall of gastric cardia

Gross description
  • Solitary or multiple tumors, usually involving outer wall of small intestine or colon
  • Firm, tan white, well circumscribed
  • Usually around 6 cm but may measure up to 20 cm
Gross images

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Cut surface of lesion

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Excised specimen in cut section

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Fibrotic nodules in pouch of Douglas

Microscopic (histologic) description
  • Mildly to moderately cellular lesion composed of stellate or spindled fibroblasts arranged haphazardly or in intersecting fascicles
  • Stroma rich in collagen (wire-like, keloidal or hyalinized)
  • Sparse intralesional mononuclear cells and peripheral lymphoid aggregates usually present
  • May have infiltrative borders
Microscopic (histologic) images

Contributed by Raul S. Gonzalez, M.D.
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Low power

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Intermediate power

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Interaction with adjacent fat

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Entrapped nerves

Negative stains
Molecular / cytogenetics description
  • No substitutions, deletions or insertions in exons 9 or 11 of KIT gene
Sample pathology report
  • Mesentery, resection:
    • Reactive fibrotic nodule, most consistent with reactive nodular fibrous pseudotumor (2.2 cm)
    • Negative for malignancy.
    • Margins of resection unremarkable.
Differential diagnosis
Board review style question #1
Which of the following abdominal lesions stains positive for CD117 by immunohistochemistry?

  1. Desmoid fibromatosis
  2. Inflammatory myofibroblastic tumor
  3. Reactive nodular fibrous pseudotumor
  4. Retroperitoneal fibrosis
  5. Sclerosing mesenteritis
Board review style answer #1
C. Reactive nodular fibrous pseudotumor

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Reference: Reactive nodular fibrous pseudotumor
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