Editorial Board Member: Raul S. Gonzalez, M.D.
Editor-in-Chief: Debra L. Zynger, M.D.
Lukas Streich, M.D.
Maryam Kherad Pezhouh, M.D., M.Sc.

Last author update: 8 February 2022
Last staff update: 10 February 2022

Copyright: 2003-2024,, Inc.

PubMed Search: Periappendicitis

Lukas Streich, M.D.
Maryam Kherad Pezhouh, M.D., M.Sc.
Page views in 2023: 11,184
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Cite this page: Streich L, Pezhouh MK. Periappendicitis. website. Accessed February 22nd, 2024.
Definition / general
  • Acute inflammation of the serosal surface of the appendix
Essential features
  • Neutrophilic infiltrate in the serosa of the appendix
  • Sparing of the appendiceal mucosa
  • Serosal fibrin deposition
  • No history of surgical manipulation
  • Appendiceal serositis, acute serositis
ICD coding
  • Periappendicitis does not have a dedicated ICD-10 code
    • ICD-10: K35.3 - acute appendicitis with localized peritonitis
    • ICD-10: K35.80 - unspecified acute appendicitis
  • Serosal surface of vermiform appendix
  • Secondary to intra-abdominal inflammatory conditions
Clinical features
Radiology description
  • Diagnosis may be suspected based on imaging findings, including appendiceal enlargement and fat stranding with inflammatory changes on CT scan (Int J Surg 2014;12:1010)
  • However, as with the clinical presentation, imaging findings overlap closely with appendicitis (Postgrad Med J 2006;82:830)
  • Imaging findings may also reflect the underlying causative process
Prognostic factors
  • Alone, it has unclear prognostic significance (Postgrad Med J 2006;82:830)
  • Disease course will be largely dictated by prompt recognition and treatment of the underlying disease
Case reports
  • Definitive management should be directed at the underlying condition (Int J Surg 2014;12:1010)
  • For infectious conditions of the peritoneum, refer to the guidelines published by the Infectious Disease Society of America
  • Conditions such as abdominal aortic aneurysm require surgical management
  • Management is generally appendectomy, although a growing body of evidence suggests conservative management with antibiotics may be sufficient
Gross description
Gross images

Contributed by Lukas Streich, M.D.


Frozen section description
  • Will show inflammatory infiltrate in the serosa with sparing of the mucosa
Microscopic (histologic) description
Microscopic (histologic) images

Contributed by Maryam Kherad Pezhouh, M.D., M.Sc.

Absent luminal inflammation

Serosal inflammation

Inflammation and edema

Neutrophils at serosa

Sparing of muscularis

Sample pathology report
  • Appendix, appendectomy:
    • Periappendicitis.
Differential diagnosis
  • Acute appendicitis:
    • Acute inflammation of the appendiceal mucosa
    • Since serosal findings are common in acute appendicitis, examination of the entire appendix might be necessary in order to exclude this entity
  • Periappendicitis due to endometriosis
  • Periappendicitis due to other nonneoplastic or neoplastic processes involving the appendix
    • Careful examination of the entire appendix can help excluding other possible etiologies
Board review style question #1
A 17 year old girl presents with a one day history of crampy right lower quadrant abdominal pain and fever. Imaging shows an enlarged appendix. Appendectomy is performed and on histologic examination the specimen shows neutrophilic infiltrate in the serosa, sparing the mucosa. What is the most likely underlying cause of periappendicitis?

  1. Acute appendicitis with perforation
  2. Acute salpingitis
  3. Inflammatory bowel disease
  4. Meckel's diverticulum
Board review style answer #1
B. The patient has periappendicitis secondary to intra-abdominal inflammatory pathology. Salpingitis is the most common cause of acute periappendicitis. While inflammatory bowel disease and Meckel diverticulum are both possible causes, they are less common. Acute appendicitis by definition will involve the mucosa of the appendix.

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Reference: Periappendicitis
Board review style question #2

You receive an appendix for microscopic examination. You note that the patient has a history of treated Crohn's colitis and is currently hospitalized after partial colectomy. On examination, the appendiceal serosa shows scattered neutrophils without other pathologic change. What is the most likely cause of this finding?

  1. Acute appendicitis
  2. Previous surgery
  3. Salpingitis
Board review style answer #2
B. Mild serosal neutrophilic infiltrate can occur after surgical manipulation of the appendix. Acute appendicitis is not the correct answer as the mucosa did not show any evidence of active inflammation. Although salpingitis is a possibility, the likelihood of that is less than mild inflammation due to prior surgery.

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Reference: Periappendicitis
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