Acute Appendicitis

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Last updated: October 28, 2021
Revisions: 40

Last updated: October 28, 2021
Revisions: 40

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Appendicitis refers to inflammation of the appendix and is a common acute surgical presentation

It most commonly affects those in their second or third decade and there is an overall lifetime risk of 7-8%. It is one of the most common causes of abdominal pain in young people and children, with around 50,000 appendicectomies performed in both children and adults a year in the UK

In this article, we shall look at the clinical features, investigations and management of acute appendicitis.


It is typically caused by direct luminal obstruction, usually secondary to a faecolith (Fig. 1) or lymphoid hyperplasia, impacted stool or, rarely, an appendiceal or caecal tumour.

When obstructed, commensal bacteria in the appendix can multiply, resulting in acute inflammation. Reduced venous drainage and localised inflammation can result in increased pressure within the appendix, in turn can result in ischaemia.

If left untreated, ischaemia within the appendiceal wall can result in necrosis, which in turn can cause the appendix to perforate.

Figure 1 – A faecolith obstructing the appendiceal lumen, resulting in acute appendicitis

Risk Factors

  • Family history
    • Twin studies suggest that genetics account for 30% of risk*
  • Ethnicity
    • More common in Caucasians
  • Environmental
    • Seasonal presentation during the summer

*No specific gene has been identified specifically, but the risk is roughly three times higher in members of families with a positive history

Clinical Features

The main symptom of appendicitis is abdominal pain. This is initially peri-umbilical, classically dull and poorly localised (from visceral peritoneum inflammation), but later migrates to the right iliac fossa, where it is well-localised and sharp (from parietal peritoneum inflammation).

Other symptoms can include vomiting (typically after the pain, not preceding it), anorexia, nausea, diarrhoea, or constipation.

On examination, there may be rebound tenderness and percussion pain over McBurney’s point (Fig. 2), as well as guarding (especially if the appendix is perforated). In severe cases, patients can show features of sepsis, being tachycardic and hypotensive, especially in untreated cases. An appendiceal abscess may also present with a RIF mass.

Specific signs that may be found on examination include*:

  • Rovsing’s sign: RIF fossa pain on palpation of the LIF
  • Psoas sign: RIF pain with extension of the right hip
    • Specifically suggests an inflamed appendix abutting psoas major muscle in a retrocaecal position

*Whilst alone they may have a poor predictive value, when combined they can be very sensitive in the conditions diagnosis

Figure 2 – McBurney’s Point (1), two thirds of the way between the umbilicus (2) and the ASIS (3)

Acute Appendicitis in Children

Whilst some cases can present classically, a high proportion of acute appendicitis in children will present in an atypical manner. Such presentations may include diarrhoea, urinary symptoms, or even left sided pain.

When examining a child with suspected appendicitis, as well as examining the gastrointestinal system, it is therefore also essential to examine the cardiorespiratory and urinary systems. In such cases, always ensure to perform a genital examination in all boys, to exclude testicular torsion or epididymitis.

Remember, a child under 6 years of age who has had symptoms for over 48 hours is significantly more likely to be suffering from a perforated appendix, therefore a period of active observation is often prudent.

Differential Diagnosis

There are a wide spectrum of potential differentials for suspected cases of appendicitis: 

  • Gynaecological: ovarian cyst rupture, ectopic pregnancy, pelvic inflammatory disease
  • Renal: ureteric stones, urinary tract infection, pyelonephritis

*If a normal appendix is found during appendicectomy, an inflamed Meckel’s diverticulum should also be checked for

Specifically in children, differentials to consider include acute mesenteric adenitis, gastroenteritis, constipation, intussusception, or urinary tract infection.


Laboratory Tests

Urinalysis should be done for all patients with suspected appendicitis to help exclude any renal or urological cause*. For any woman of reproductive age, a pregnancy test is also essential.

Routine bloods, importantly FBC and CRP, should be requested to assess for raised inflammatory markers, as well as baseline blood tests required for potential pre-operative assessment. A serum β-hCG may also be taken, if ectopic pregnancy still has not been excluded.

*Leucocytes can be present in the urine in low levels for those with an appendicitis, especially if the appendix lies on the bladder


Imaging is not essential to diagnose an appendicitis, as cases can be a clinical diagnosis. Indeed, in certain cases (especially paediatrics), serial examinations may be the only method employed to make the diagnosis.

Ultrasound scan or CT imaging (Fig. 3) are often requested if the clinical features are inconclusive and an alternative diagnoses are equivocal:

  • Ultrasound – good first line investigation (especially with a transvaginal approach) if the differential includes gynaecological pathology
    • Useful in children as can minimise radiation exposure
  • Computed Tomography – Good sensitivity and specificity, able to delineate multiple differentials including gastrointestinal and urological causes
Fig 2 - CT scan showing an acute appendicitis, measuring 17.1mm diameter

Figure 3 – CT scan showing an acute appendicitis, measuring 17.1mm diameter

Risk Stratification Scores

Several risk stratification scores have been developed in an attempted to assist in the diagnosis of appendicitis, based on clinical and radiological evidence.

The RIFT study compared multiple risk prediction models, showing the best predictors for acute appendicitis were:

  • Men – Appendicitis Inflammatory Response Score
  • Women – Adult Appendicitis Score
  • Children – Shera score

A risk score calculator using these parameters can be found here and can be used to aid clinical decision making


The current definitive treatment for appendicitis is laparoscopic appendicectomy (Fig. 4).

There is some debate surrounding the use of conservative antibiotic therapy in uncomplicated appendicitis; a Cochrane analysis found that appendicectomy should remain the standard treatment for acute appendicitis. Indeed, primary antibiotic treatment for simple inflamed appendix may be successful, but has a failure rate of 25-30 % at one year.

If cases of an appendiceal mass, antibiotic therapy is favoured, with an interval appendectomy then performed approximately 6-8 weeks later

Surgical Intervention

Laparascopic appendectomy* (Fig. 4) still remains the gold standard for treating appendicitis, due to a low morbidity from the procedure. In females it also allows for better visualisation of the uterus and ovaries, for assessment of any gynaecological pathology.

The appendix should routinely be sent to histopathology to look for malignancy (found in 1%, typically carcinoid, adenocarcinoma, or mucinous cystadenoma malignancy). As per any laparoscopic procedure, the entirety of the abdomen should be inspected for any other evident pathology, including checking for any Meckel’s diverticulum present.

*An open approach (classically via a Lanz incision) may be used in pregnancy and is still used globally in some healthcare systems, yet the laparoscopic approach has been shown to reduced hospital stay and permit earlier return to baseline activity

Fig 4 - Laparoscopic appendicectomy.

Figure 4 – Stages of a laparoscopic appendicectomy


The mortality associated with appendicitis in developed health systems is low (0.1% to 0.24 %). The complications of acute appendicitis include:

  • Perforation, if left untreated the appendix can perforate and cause peritoneal contamination
    • This is particular note in children who may have a delayed presentation
  • Surgical site infection
    • Rates vary depending on simple or complicated appendicitis (ranging 3.3-10.3 %)
  • Appendix mass, where omentum and small bowel adhere to the appendix
  • Pelvic abscess
    • Presents as fever with a palpable RIF mass, can be confirmed CT scan for confirmation; management is usually with antibiotics and percutaneous drainage of abscess

Key Points

  • Appendicitis refers to inflammation of the appendix, most common in those in their second decade
  • The main symptom is abdominal pain, initially dull, peri-umbilical, and poorly localised, before migrating to the right iliac fossa and becomes well-localised and sharp
  • Diagnosis is typically clinical, however ultrasound or CT imaging can help in cases of clinical equipoise
  • Management is typically with laparoscopic appendicectomy, however some cases can be treated conservatively with antibiotics