Appendicitis may be defined as inflammation of the appendix.

Acute appendicitis is an common surgical pathology and presents with an acute abdomen. There are upwards of 35,000 cases in the UK each year.

Appendicitis statistics

Appendicitis has a slight male preponderance and is uncommon at the extremes of age. The majority of cases occur in those aged 15-59 years-old.


The appendix is a short appendage, normally 5-10 cm long, that opens onto the caecum.

The appendix may also be referred to as the vermiform (to resemble a worm) appendix. It is a blind-ended tube that arises at the posteromedial aspect of the caecum at the convergence of the taeniae coli.

Whilst the base is consistent the appendix itself has a variable position. The majority are either retrocaecal (around 60%) or pelvic (around 20%). The remaining are preileal, postileal, subcaecal or paracaecal. 

The appendiceal mesentery hangs from the terminal ileum and contains the appendiceal branch of the ileocolic artery (from the superior mesenteric artery).

Aetiology & pathophysiology

Appendicitis is normally caused by obstruction of the lumen of the appendix.

Appendiceal obstruction may result from a variety of causes. One of the most common causes are faecoliths. These are hard collections of stool that form and block the appendix. Other causes include lymphoid hyperplasia, fibrous stricture or carcinoid tumours.

Appendicitis is uncommon at the extremes of age. The young have a relatively wide appendiceal lumen, whilst in the elderly, it is almost entirely obliterated. 

Obstruction of the appendiceal lumen causes stasis and resultant bacterial overgrowth. The proliferation of bacteria leads to an increase in the intra-luminal pressure. As the pressure rises in the appendix it causes venous and lymphatic congestion. As the pressure rises further, the arterial supply to the appendix becomes compromised leading to gangrene, perforation and generalised peritonitis. 

The risk of perforation is 15-35% at 72 hours with an additional 5% risk for every 12 hours thereafter. 

Appendicitis pathophysiology

Clinical features

Patients classically complain of a colicky, peri-umbilical pain which migrates to the right iliac fossa (RIF) and becomes constant.

Common clinical features associated with acute appendicitis include nausea, anorexia and constipation. Diarrhoea may be a feature in patients with ileal irritation. 

Acute appendicitis is uncommon at the extremes of age where it also tends to have an atypical presentation. Pregnant women may have a displaced appendix resulting in flank pain. A high degree of clinical suspicion is required as delayed treatment results in high mortality in both the mother and foetus. 


  • RIF pain
  • Nausea
  • Anorexia
  • Constipation


  • RIF tenderness
  • Percussion tenderness
  • Localised guarding
  • Tachycardia
  • Pyrexia

Additional signs

Rovsing sign: Pain in the RIF of palpation of the LIF.

Psoas sign: Pain in the RIF on extension of the right hip.

Obturator sign: Pain in the RIF on internal rotation of a flexed right hip.

Appendicitis signs and symptoms

Generalised peritonitis

In those who present late or the diagnosis is missed, generalised peritonitis may occur. Examination will reveal a rigid tender abdomen with absent bowel sounds. These patients will be unwell and require prompt management.

Investigations & diagnosis

The diagnosis of appendicitis is normally based on the history and examination.


  • Observations
  • Urine dip
  • Pregnancy test


  • FBC
  • U&Es
  • CRP
  • LFTs
  • Amylase
  • Group & save
  • Clotting screen

Inflammatory markers are normally elevated with the exception of those presenting early in the disease process.


Ultrasound: May identify appendicitis, though sensitivity is user-dependent. Pelvic ultrasound is often used in female patients where the differential includes gynaecological pathology. 

Computed tomography: The use of CT to confirm the diagnosis of appendicitis is becoming increasingly commonplace. 

Alvarado score

The Alvarado score gives an estimate of the likelihood of appendicitis based upon two major and six minor criteria.

Alvarado score


Appendicitis may be managed in a conservative or surgical manner.


A number of studies* have confirmed that uncomplicated acute appendicitis may be treated initially with antibiotics (augmentin is commonly used). A proportion of these patients, 27% in one study, required surgery within one year. Beyond this, there would likely continue to be a risk of re-developing appendicitis. 



In the UK, the majority of patients with suspected appendicitis receive surgical management in the form of a laparoscopic appendicectomy. This is a minimally invasive procedure with a high success and low complication rates.

Pre-operatively, antibiotic therapy should be commenced (co-amoxiclav is commonly used) and continued for 7 days only if peritonitis is noted intra-operatively. Depending on the operative findings a temporary drain may be inserted.

Surgical management in those with an appendiceal mass would likely be complicated by inflammation and adhesions. As such simple localised cases may be treated with antibiotics alone. Larger abscesses may benefit from a percutaneous drain and complicated loculated disease may necessitate surgical intervention.

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