Benign tumors
Fibrous obliteration

Topic Completed: 27 December 2018

Minor changes: 4 August 2020

Copyright: (c) 2002-2018,, Inc.

PubMed Search: Fibrous obliteration appendix

Raul S. Gonzalez, M.D.
Page views in 2020: 10,270
Page views in 2021 to date: 697
Cite this page: Gonzalez R. Fibrous obliteration. website. Accessed January 23rd, 2021.
Definition / general
  • Benign spindle cell proliferation replacing the lumen of the appendix
Essential features
  • Incidental, benign finding of the appendix
  • May obliterate mucosa and lumen
  • Wall becomes replaced with spindle cell proliferation and adipose tissue
ICD coding
    ICD-10 Coding:
  • K38.8: other specified diseases of appendix
  • May occur just in tip or involve entire appendix
Clinical features
Gross description
  • Usually no gross tumor
  • Usually affects distal tip, may affect entire lumen
Microscopic (histologic) description
  • Lumen replaced by spindle cells in loose fibromyxoid background with chronic inflammatory cells (including eosinophils), hypertrophied nerve bundles, neuroendocrine cells, adipose cells and collagen
  • Loss of lymphoid follicles, mucosa and crypts
Microscopic (histologic) images

Contributed by Raul Gonzalez, M.D.

Obliterated lumen

Adipose and spindle cells

Bland spindle cells

Superimposed acute appendicitis

Positive stains
Differential diagnosis
  • Well differentiated neuroendocrine tumor: definite insular pattern of neoplastic cells, extending into muscularis propria, associated with gross nodule or thickening of appendiceal wall
  • Neurofibroma: arises in NF1 patients; thickens wall but does not obliterate lumen (Histopathology 1987;11:851)
  • True intramucosal neuroma: primarily affects the mucosa; does not obliterate the lumen
  • Appendiceal mucosal Schwann cell proliferation: no obliteration of lumen; may be more common in appendiceal diverticula (Int J Surg Pathol 2013;21:603)
Board review style question #1
    Which of the following is true about fibrous obliteration of the appendix?

  1. Can show marked cytologic atypia, mimicking sarcoma
  2. Generally only involves the base of the appendix
  3. May contain chronic inflammation and adipocytes
  4. Suggests an underlying diagnosis of neurofibromatosis type 1
Board review style answer #1
C. May contain chronic inflammation and adipocytes

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Board review style question #2

    A young patient is diagnosed with acute appendicitis and the appendix specimen shows the pictured process occupying the lumen. Immunohistochemistry for what protein would be positive in this process?

  1. MUC4
  2. Myogenin
  3. S100
  4. SMA
Board review style answer #2
C. S100

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