Acute Appendicitis

Appendicitis refers to inflammation of the appendix. It is caused by direct luminal obstruction, usually secondary to 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 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

  • 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).

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 in a retrocaecal position

The clinical signs have poor predictive value alone, but are stronger in concert, hence the rationale for clinical risk scores (as discussed below). A pelvic examination is 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:

  • 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, 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. 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

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, scores such as the Alvarado Score and the Appendicitis Inflammatory Response (AIR) Score should only be used to assist 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).


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.

*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.

Surgical Intervention

Laparascopic appendectomy* (Fig. 3) still remains the gold standard for treating appendicitis, due to a very low morbidity from the procedure and the risk of a possible readmission if treated with antibiotic therapy alone. In females it also allows for 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. 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 earlier return to baseline activity.

Fig 4 - Laparoscopic appendicectomy.

Fig. 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
  • 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.


Question 1 / 4
Which of the following age groups most commonly develop acute appendicitis


Question 2 / 4
Psoas sign is associated with which position of the appendix?


Question 3 / 4
Which of the following statements is NOT true about pre-operative evaluation and management of appendicitis patients?


Question 4 / 4
A 22yr old patient is admitted with a 2 day history of abdominal pain. He reports it started centrally but now is focused to the RIF. He is pyrexial and has vomited twice. he has RIF tenderness and is Rovsing's sign positive. His WCC is 22.0 and CRP is 121, remainder of his bloods unremarkable. Which one of the following should not be part of your management plan?


Further Reading

Acute appendicitis: modern understanding of pathogenesis, diagnosis, and management.
Bhangu A et al., The Lancet

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