Appendix
Benign tumors
Fibrous obliteration
Author: Raul S. Gonzalez, M.D.
Editorial Board Member: Catherine E. Hagen, M.D.
Editor-in-Chief: Debra L. Zynger, M.D.
Last author update: 28 April 2021
Last staff update: 15 October 2021
Copyright: 2002-2024, PathologyOutlines.com, Inc.
PubMed Search: Fibrous obliteration appendix
Table of Contents
Definition / general | Essential features | Terminology | ICD coding | Epidemiology | Sites | Etiology | Clinical features | Gross description | Microscopic (histologic) description | Microscopic (histologic) images | Positive stains | Sample pathology report | Differential diagnosis | Board review style question #1 | Board review style answer #1 | Board review style question #2 | Board review style answer #2Cite this page: Gonzalez RS. Fibrous obliteration. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/appendixfibrousobliteration.html. Accessed April 23rd, 2024.
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
Terminology
- Has been given several other names, including neurogenic appendicitis, appendiceal neuroma, neuronal hyperplasia and neurogenic appendicopathy (Am J Surg Pathol 1986;10:801, Eur J Pediatr Surg 2013;23:238)
ICD coding
- ICD-10: K38.8 - other specified diseases of appendix
Epidemiology
- Incidence may vary by population, from < 1% to ~30% (Indian J Surg 2018;80:48, Ann Ital Chir 2017;88:519, Am J Surg Pathol 1986;10:801, J Urol 1992;148:41)
- Incidence higher in elderly patients (J Urol 1992;148:41)
Sites
- May occur just in tip or involve entire appendix
Etiology
- Postulated to be secondary to repeated bouts of appendiceal inflammation (Histopathology 1987;11:843)
Clinical features
- May occur in children and may mimic acute appendicitis clinically (Eur J Pediatr Surg 2013;23:238)
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 S. Gonzalez, M.D.
Obliterated lumen
Adipose and spindle cells
Bland spindle cells
Superimposed acute appendicitis
Positive stains
- Spindle cells: S100, chromogranin, neuron specific enolase
Sample pathology report
- Appendix, appendectomy:
- Appendix with fibrous obliteration
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?
- Can show marked cytologic atypia, mimicking sarcoma
- Generally only involves the base of the appendix
- May contain chronic inflammation and adipocytes
- Suggests an underlying diagnosis of neurofibromatosis type 1
Board review style answer #1
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?
- MUC4
- Myogenin
- S100
- SMA
Board review style answer #2
