Appendix

Other nonneoplastic

Inverted appendix



Last author update: 13 December 2023
Last staff update: 13 December 2023

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PubMed Search: Inverted appendix

Mahzad Azimpouran, M.D.
Danielle Hutchings, M.D.
Page views in 2023: 1,073
Page views in 2024 to date: 240
Cite this page: Azimpouran M, Hutchings D. Inverted appendix. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/appendixinverted.html. Accessed February 22nd, 2024.
Definition / general
  • Appendix that inverts / intussuscepts and is pulled into the lumen of the cecum
Essential features
  • Inverted appendix may appear as a polyp or mass in the cecum on endoscopy or imaging
  • Histological clues on endoscopically retrieved specimens include
    • Dome-like tissue configuration with mucosa on the convex surface
    • Deep, smooth muscle component with ganglion cells (muscularis propria)
    • Lymphoid aggregates or prominent submucosal adipose tissue
Terminology
  • Appendiceal intussusception
ICD coding
  • ICD-10
    • K38.8 - other specified diseases of appendix
    • K38.9 - disease of the appendix, unspecified
Epidemiology
Sites
Pathophysiology
Etiology
Clinical features
Diagnosis
Radiology description
Radiology images

Images hosted on other servers:
CT demonstrating an intraluminal tubular structure

CT demonstrating an intraluminal tubular structure

Intraluminal protruding mass with central fat component

Intraluminal protruding mass with central fat component

Cecal thickening without visualization of appendix

Cecal thickening without visualization of appendix

Prognostic factors
  • Benign lesion, unless it arises in associated with an underlying neoplasm
  • Rarely, perforation with associated peritonitis may occur in polypectomy specimens (Am J Gastroenterol 1982;77:556)
Case reports
Treatment
  • Appendectomy with resection of cecal cuff is typically recommended to reduce risk of recurrence (Am J Surg 2009;198:122)
Clinical images

Images hosted on other servers:
Elongated lesion at appendiceal orifice

Elongated lesion at appendiceal orifice

Tubular structure in cecum

Tubular structure in cecum

Endoscopy

Endoscopy

Gross description
  • Elongated to polypoid mass in the proximal cecum at the usual location of the appendiceal orifice
  • May show foreskin and glans-like morphology (Histopathology 2019;74:853)
  • Anatomical classification of inverted appendix; McSwain classification: 5 types of appendiceal intussusceptions (Am J Surg 2009;198:122)
    • Type I: tip of the appendix is invaginated into the proximal appendix
    • Type II: invagination starts at some point along the length of the appendix and the intussusception is the appendiceal body
    • Type III: invagination starts at the junction of the appendix and cecum; the intussusception is the cecum
    • Type IV: proximal appendix is invaginated into the distal appendix; retrograde intussusception
    • Type V: appendix is completely invaginated into the cecum
Gross images

Contributed by Mahzad Azimpouran, M.D. and Danielle Hutchings, M.D.
Elongated tubular lesion

Elongated tubular lesion

Inversion of appendiceal base

Inversion of appendiceal base

Inverted appendix associated with mucinous neoplasm

Associated with mucinous neoplasm

Serosal surface of inverted appendix

Serosal surface

Microscopic (histologic) description
  • Dome shaped configuration of tissue covered by colonic mucosa on the outer surface
  • Presence of thick smooth muscle with ganglion cells (muscularis propria)
  • Lymphoid aggregates
  • Submucosal adipose tissue
  • Reference: Histopathology 2019;74:853
Microscopic (histologic) images

Contributed by Mahzad Azimpouran, M.D. and Danielle Hutchings, M.D.
Dome shaped configuration

Dome shaped configuration

Polypoid configuration

Polypoid configuration

Ganglion cells aggregates

Ganglion cell aggregates

Ganglion cells and nerves

Ganglion cells and nerves

Lymphoid aggregates

Lymphoid aggregates

Appendiceal mucinous neoplasm

Appendiceal mucinous neoplasm

Positive stains
  • S100: highlights ganglion cells and nerves in myenteric plexus of muscularis propria
  • SMA: highlights smooth muscle of muscularis propria
Sample pathology report
  • Appendix, appendectomy:
    • Inverted appendix
    • No dysplasia or malignancy identified

  • Cecal polyp, polypectomy:
    • Polypoid colonic tissue with underlying adipose tissue and muscularis propria consistent with inverted appendix
Differential diagnosis
Board review style question #1

A 44 year old woman underwent screening colonoscopy. The endoscopist noted a polypoid mass arising in the cecum and performed endoscopic polypectomy. The findings are pictured above. Which of the following is a key microscopic feature of this entity?

  1. Absence of ganglion cells
  2. Absence of submucosal adipose tissue
  3. Ganglion cells embedded in thick smooth muscle bundles
  4. Sessile configuration of the lesion
Board review style answer #1
C. Ganglion cells embedded in thick smooth muscle bundles. The presence of thick smooth muscle bundles of muscularis propria containing ganglion cells and nerve fibers is a key microscopic feature. Answer B is incorrect because the presence, rather than absence, of submucosal adipose tissue is a microscopic feature of inverted appendix. Answer A is incorrect because the presence of ganglion cells is a key to the identification of muscularis propria. Answer D is incorrect because the lesion is typically elongated, polypoid or dome shaped rather than sessile.

Comment Here

Reference: Inverted appendix
Board review style question #2

A 56 year old woman with a history of cecal mass on imaging underwent partial cecectomy with appendectomy. The gross findings are pictured above. What is true of this diagnosis?

  1. It is associated with endometriosis
  2. More common in men than women
  3. Resection of the lesion is necessary for the diagnosis
  4. Resection was inappropriate management for this patient
Board review style answer #2
A. It is associated with endometriosis. The lesion shown is an inverted appendix, which can occur without any underlying abnormality or may be associated with anatomical variations or pathologic conditions, such as endometriosis or appendiceal neoplasm. Answer B is incorrect because inverted appendix is more common in women than men. Answer C is incorrect because though it may be diagnostically challenging in some cases, it is possible to diagnose on radiographic imaging or colonoscopy. Answer D is incorrect because appendectomy with resection of cecal cuff is generally recommended for inverted appendix to avoid recurrence.

Comment Here

Reference: Inverted appendix
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