Acute Appendicitis

Original Author: Abarna Ramanathan
Last Updated: September 1, 2016
Revisions: 26

Appendicitis refers to inflammation of the appendix. It is caused by direct luminal obstruction – usually secondary to faecolith, lymphoid hyperplasia, impacted stool or, rarely, an appendiceal or caecal tumour (more common in patients presenting later in life).

It typically affects those in their second or third decade, and has a lifetime risk of 7-8%.

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

Risk Factors

There are several risk factors for developing acute appendicitis:

  • Family history: Twin studies suggest that genetics account for 30% of risk. No gene has been identified but the risk is roughly three times higher in members of families with a positive history.
  • 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

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).

Fig 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 at 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 (suggests inflamed appendix abutting psoas major muscle).

The clinical signs have poor predictive value alone, but are stronger in concert, hence the rationale for clinical risk scores. The most widely used scoring system is the Alvarado score.

Remember that a pelvic examination is required in females of reproductive age if ovarian pathology is suspected.

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:

  • Gynaecological: Pelvic inflammatory disease.
  • Renal: Ureteric stones, urinary tract infection, pyelonephritis.
  • Gastrointestinal: Diverticulitis, IBD, mesenteric adenitis, or Meckel’s diverticulum
    • If a normal appendix is found during appendicectomy, an inflammed Meckel’s diverticulum should also be looked for
  • Urological: Testicular torsion.


Laboratory Tests

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

Typically a FBC and CRP are requested to assess for raised inflammatory markers (raised WCC and CRP), as well as baseline blood tests required for a pre-operative assessment as surgical intervention is likely. 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. A trans-abdominal ultrasound (USS) or a CT scan may be done if the signs and symptoms are inconclusive and an alternative diagnosis is sought. A CT scan is useful in elderly patients due to the potential for caecal malignancy causing appendicitis, where treatment would clearly be different.

  • Trans-abdominal USS: Good sensitivity and specificity (86% and 81% respectively) and most useful in children, who have less abdominal fat and will be exposed to lower levels of 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

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


Alvarado Score

The Alvarado Score aims to quantify the likelihood of a patient having appendicitis. It produces a risk score; 1-4 = low risk, 5-6 = intermediate risk, and 7-10 = high risk.

Fig 3 - The Alvarado Score.

Fig 3 – The Alvarado Score.



The current definitive treatment for appendicitis is 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.

A current theory suggests that appendicitis appears in two separate forms. One type as a simple reversible inflammation, whilst a second type will rapidly progress to gangrene and perforation; the former can be treated successfully with antibiotics whilst the latter requires surgical intervention. The triad of CRP<60, WBC <12 x 10^9 and age<60 appears to predict antibiotic success.

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. This may be due to inappropriate case selection.

Surgical Intervention

Laparascopic appendectomy still remains the gold standard for treating appendicitis, due to a very low morbidity from the procedure and the risk of possible readmission with antibiotic therapy.

In females this also allows better visualisation of the uterus and ovaries. The appendix should be sent to histopathology to look for malignancy (found in 1%), typically carcinoid, adenocarcinoma, or mucinous cystadenoma malignancy.

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 earlier return to baseline activity.

Fig 4 - Laparoscopic appendicectomy.

Fig 4 – 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
  • Wound 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 (in 9.4%, more common in perforation)
    • 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.

Further Reading

Acute appendicitis: modern understanding of pathogenesis, diagnosis, and management.
The Lancet

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