Part of the TeachMe Series

Acute Appendicitis

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Original Author(s): Abarna Ramanathan
Last updated: September 27, 2018
Revisions: 34

Original Author(s): Abarna Ramanathan
Last updated: September 27, 2018
Revisions: 34

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Appendicitis refers to inflammation of the appendix.

It is caused by direct luminal obstruction, usually secondary to a faecolith but may also be due to lymphoid hyperplasia, impacted stool or, rarely, an appendiceal or caecal tumour. It typically affects those in their second or third decade and there is a lifetime risk of 7-8%.

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

Risk Factors

  • Family history
    • Twin studies suggest that genetics account for 30% of risk*
  • Ethnicity
    • More common in Caucasians, yet ethnic minorities are at greater risk of perforation if they do get appendicitis
  • Environmental
    • Seasonal presentation during the summer

*No 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, dull, and poorly localised, but later migrates to the right iliac fossa, where it is well-localised and sharp. Other possible symptoms include vomiting (typically after the pain, not preceding it), anorexia, nausea, diarrhoea, or constipation.

Fig 1 - McBurney's Point (1), two thirds of the way between the umbilicus (2) and the ASIS (3).

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

On examination, patients may be tachycardic, tachypnoeic, and pyrexial. When examining the abdomen, the most specific findings are rebound tenderness and percussion pain over McBurney’s point (Fig.1), as well as potential signs of guarding (if perforated). An appendiceal abscess may also present with a RIF mass.

There are two “textbook signs” that may be found on examination:

  • 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 the clinical signs alone have poor predictive value, when combined they can be very sensitive in the conditions diagnosis.

A pelvic examination may be required in females of reproductive age to assess for any potential gynaecological pathology

Differential Diagnosis

The most important other diagnosis to consider in the younger female patient is gynaecological pathology, especially ectopic pregnancy or ovarian cyst rupture.

Other differential diagnoses include:

  • Renal: ureteric stones, urinary tract infection, pyelonephritis
  • Gastrointestinal: mesenteric adenitis, diverticulitis, inflammatory bowel disease, or Meckel’s diverticulum*
  • Urological: Testicular torsion, epididymo-orchitis
  • Gynaecological: pelvic inflammatory disease

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


Laboratory Tests

Urinalysis should be done for all patients with suspected appendicitis to exclude any UTI or other renal / urological cause (albeit leucocytes can be present in those with an appendicitis). For any woman of reproductive age, a pregnancy test is also vital.

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.


Imaging is not required to diagnose or treat appendicitis, as most cases should be a clinical diagosis.

A trans-abdominal ultrasound or a CT scan may be requested if the clinical features are inconclusive and an alternative diagnosis is sought:

  • Trans-abdominal US – Good sensitivity and specificity (86% and 81% respectively) and most useful in children, who have less abdominal fat and should not be exposed to radiation
  • CT scan – More commonly used in older patients, especially to identify any potential malignancy masquerading as or causing an appendicitis
Fig 2 - CT scan showing an acute appendicitis, measuring 17.1mm diameter

Figure 2 – CT scan showing an acute appendicitis, measuring 17.1mm diameter

Risk Stratification Scores

Table 1 – Parameters involved in the AIR score

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

However, these scores, such as the Alvarado Score and the Appendicitis Inflammatory Response (AIR) Score, should only be used to assist the surgeon in their decision making and not replace their clinical judgement.

The AIR score is a validated score (Table 1) that aims to triage patient into: low risk (0-4, no intervention required), intermediate risk (5-8, for inpatient observation or further imaging advised), high risk (9-12, surgical exploration recommended).

Risk stratification scores are still not routinely used in clinical practice and ongoing research aims to appraise these scores for best practice.


The current definitive treatment for appendicitis is laparoscopic appendicectomy.

However, there is some debate surrounding the use of conservative antibiotic therapy in uncomplicated appendicitis; a recent Cochrane analysis found that whilst appendicectomy should remain the standard treatment for acute appendicitis, further research is still warranted*.

Experience has shown that primary antibiotic treatment for simple inflamed appendix can be successful but has a failure rate of 25-30 % at one year.

Surgical Intervention

Laparascopic appendectomy* (Fig. 3) 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.

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 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 3 – Stages of a laparoscopic appendicectomy


The mortality associated with appendicitis in developed health systems is low (0.09% to 0.24 %). The complications of acute appendicitis include:

  • Perforation, if left untreated the appendix can perforate and cause peritoneal contamination
  • 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
    • Traditional management involves conservative approach with antibiotics, yet much debate remains surrounding the role of surgical intervention
  • Pelvic abscess
    • Presents as fever with a palpable RIF mass, yet typically requires US scan or CT scan for confirmation
    • Management is usually with antibiotics and percutaneous drainage of abscess. Any immediate surgery is associated with increased morbidity and ileo-caecal resection
    • Follow-up with CT scan after conservative treatment is recommended in patients >40yrs, due to around 2% prevalence of concurrent malignancy.

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