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Acute appendicitis

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Updated 2024 IDSA guidelines for diagnostic imaging and microbiological testing in acute appendicitis.



Acute appendicitis is a disease resulting from acute inflammation of the vermiform appendix.
Acute appendicitis is initiated by a process that causes obstruction of the appendiceal lumen, such as fecaliths, lymphoid hyperplasia, parasites, Crohn's disease, foreign bodies, or neoplasms.
The incidence of acute appendicitis is estimated at 110 per 100,000 person-years in the US, with a male predominance.
Disease course
Progressive luminal obstruction is associated with inflammation and distension of the appendix, leading to suppurative transmural inflammation, ischemia, infarction, and perforation. Perforated appendicitis progresses to generalized peritonitis and intra-abdominal abscess formation.
Prognosis and risk of recurrence
The mortality rate associated with non-perforated appendicitis is 0.8 per 1,000 individuals, whereas, for perforated appendicitis, it increases to 5.1 per 1,000 individuals. The risk of recurrent appendicitis after interval appendicectomy is about 20% within a year. Recurrent appendicitis may also occur in the setting of previous appendicectomy in patients with a long appendiceal stump.


Key sources

The following summarized guidelines for the evaluation and management of acute appendicitis are prepared by our editorial team based on guidelines from the Infectious Diseases Society of America (IDSA 2024), the Society of American Gastrointestinal and Endoscopic Surgeons (SAGES 2024), the American College of Radiology (ACR 2022), the World Society of Emergency Surgery (WSES 2020), the Eastern Association for the ...
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Classification and risk stratification

Risk stratification: as per IDSA 2024 guidelines, assess disease severity for risk stratification in patients with complicated intra-abdominal infections. Consider using the APACHE II as the preferred severity of illness score for risk stratification within 24 hours of hospital or ICU admission in adult patients with complicated intra-abdominal infection, if a severity of illness score is used.
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Diagnostic investigations

Abdominal ultrasound: as per WSES 2020 guidelines, obtain diagnostic imaging in patients with suspected appendicitis after an initial assessment and risk stratification using clinical scores.
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  • CT and MRI

  • Blood cultures

Diagnostic procedures

Explorative laparoscopy
As per WSES 2020 guidelines:
Perform explorative laparoscopy in patients with negative imaging but progressive or persistent pain to establish/exclude the diagnosis of acute appendicitis or alternative diagnoses.
Avoid obtaining cross-sectional imaging (CT) in < 40 years old high-risk patients with AIR score 9-12, Alvarado score 9-10 and AAS ≥ 16 before proceeding to diagnostic and/or therapeutic laparoscopy.

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  • Histopathology

Medical management

Nonoperative management: as per WSES 2020 guidelines, consider offering nonoperative management with antibiotics as a safe alternative to surgery in selected patients with uncomplicated acute appendicitis and absence of appendicolith, recognizing the possibility of failure and misdiagnosing complicated appendicitis.
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  • Analgesic therapy

Perioperative care

Preoperative antibiotics: as per WSES 2020 guidelines, administer a single preoperative dose of broad spectrum antibiotics in patients with acute appendicitis undergoing appendectomy.

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  • Intraoperative grading systems

  • Postoperative antibiotics

  • Postoperative nasogastric tube

  • Postoperative diet

Surgical interventions

Timing of surgery
As per WSES 2020 guidelines:
Plan laparoscopic appendectomy for the next available operating list within 24 hours in patients with uncomplicated acute appendicitis, minimizing the delay wherever possible.
Do not delay appendectomy in patients with acute appendicitis requiring surgery beyond 24 hours from the admission.

More topics in this section

  • Laparoscopic appendectomy

  • Technical considerations for surgery

  • Intra-abdominal cultures

Specific circumstances

Pediatric patients, diagnostic imaging
As per IDSA 2024 guidelines:
Consider obtaining abdominal ultrasound as the initial imaging for the diagnosis of acute appendicitis in pediatric and adolescent patients with suspected acute appendicitis.
Consider obtaining abdominal MRI or CT rather than another ultrasound if the initial ultrasound is equivocal/nondiagnostic and clinical suspicion persists.

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  • Pediatric patients (laboratory tests)

  • Pediatric patients (management)

  • Pregnant patients (diagnostic imaging)

  • Pregnant patients (laboratory tests)

  • Pregnant patients (management)

  • Elderly patients

  • Patients with obesity

  • Patients with immunosuppression