Acute appendicitis describes the acute inflammation of the vermiform appendix. It is typically caused by infection secondary to luminal obstruction with faecolith, impacted normal stool, lymphoid hyperplasia or a tumour, and is most common between the ages of 10 and 20. It is the most common abdominal surgical emergency worldwide, with a lifetime risk of approximately 7-8%. Definitive treatment is surgical removal of the appendix.


  • Incidence: 110.00 cases per 100,000 person-years
  • Peak incidence: 20-30 years
  • Sex ratio: more common in males 1.5:1
Condition Relative
Pelvic inflammatory disease2.73
Acute cholecystitis1.27
Acute appendicitis1
Ectopic pregnancy0.36
Small bowel obstruction0.18
<1 1-5 6+ 16+ 30+ 40+ 50+ 60+ 70+ 80+


Risk factors for the development of acute appendicitis are:
  • Male sex
    • Lifetime risk for acute appendicitis is 8.6% in males and 6.9% in females
    • However, studies have shown that females are twice as likely to undergo an appendicectomy
  • Age 10-20 years
    • Appendicitis affects adolescents and young adults most commonly
  • Positive family history
    • Studies have shown that the risk of acute appendicitis is approximately 3 times higher in those with a positive family history
    • No causative gene has been identified
  • Caucasian ethnicity: the reason for this is largely unknown


Appendicitis occurs when there is acute inflammation of the appendix. It is thought to be due to obstruction of the lumen due to:
  • Faecolith
    • This is a hard stony mass of faeces
    • It is the most common cause in adults
  • Impacted normal stool
    • This can occur in patients with chronic constipation
    • This is common in children due to higher rates of constipation
  • Lymphoid hyperplasia
    • Hyperplasia of the submucosal lymphoid follicles is a common cause in children and adolescents
    • Most commonly occurs due to a viral infection
  • Tumour
    • Tumours are a rare cause, occurring in only 1% of cases
    • A colonoscopy should be considered for patients >50 years with appendicitis due to increased risk of colon cancer

Luminal obstruction causes a cascade of events which ultimately leads to inflammation within the appendix:

Obstruction of the lumen → lumen fills with mucus → increased intraluminal pressure → reduced blood flow to the appendix → resident bacteria in the appendix multiply (most commonly B.fragilis and E.coli) → inflammation and ischaemia of the appendix → perforation → peritonitis

It is important to note that not all cases of acute appendicitis progress to perforation:
  • 30% of cases of acute appendicitis progress to perforation and peritonitis if left untreated
  • It takes on average 72 hours from onset of obstruction to appendiceal perforation

Clinical features

The diagnosis of appendicitis should be made based on a detailed history and examination. The classical features of appendicitis are:
  • Abdominal pain (95%)
    • This is the most common presenting complaint in patients with acute appendicitis
    • Classically, there is dull and poorly-localised peri-umbilical or epigastric pain which becomes sharper and migrates to the right iliac fossa within 1-12 hours
    • The abdominal pain is often worse on movement, such as coughing or driving over speed bumps
    • On examination there may be rebound tenderness and guarding on palpation of McBurney's point (two-thirds of the way between the umbilicus and anterior superior iliac spine)
    • Rovsing's sign describes the phenomenon of pain in the right iliac fossa on palpation of the left iliac fossa: this sign has an 84% specificity for acute appendicitis but only 30% sensitivity
  • Nausea and vomiting (75%)
    • Typically occurs after the development of pain
    • Often accompanied by loss of appetite
    • Profuse vomiting may indicate the presence of peritonitis
  • Low-grade pyrexia
    • If a high-grade fever is present then this may indicate peritonitis or an alternative diagnosis is more likely
    • Facial flushing may also be present

If a patient has developed peritonitis as a result of a perforated appendix, then additional symptoms/signs may be present, including:
  • Tachycardia and/or hypotension
    • These are signs of septic shock
  • Tense, rigid abdomen
    • This may be accompanied with reduced bowel sounds
    • This may indicate a peritonitic abdomen as a result of a perforated appendix

It is important to note that only 50% of patients with acute appendicitis have the classical symptoms and signs and this may be influenced by the following:
  • Age
    • Older patients may have minimal pain
    • Younger patients may have vague abdominal pain and be withdrawn
  • Pregnancy
    • During pregnancy the appendix may be displaced by a gravid uterus, causing pain outside of the expected area
    • In first-trimester pain usually occurs in the right iliac fossa
    • In second and third-trimester pain typically occurs in right upper quadrant or right flank
  • Normal variation in the anatomical position of the appendix: this may cause significant variation in the location of pain


Patients with acute abdominal pain typically present to the emergency department. If acute appendicitis is suspected, they should be assessed by the general surgery team. Although acute appendicitis is predominantly a clinical diagnosis, although it can be supported by simple laboratory tests including:
  • Bloods
    • FBC: neutrophil-predominant leucocytosis is present in 80-90% of cases
    • CRP: typically raised in acute appendicitis although there is no cut-off value
  • Urinalysis
    • May be used to help exclude a urinary tract infection, although 50% of cases of acute appendicitis may have an abnormal urinalysis result
    • A pregnancy test is a vital investigation for all women of child-bearing age to exclude pregnancy, including an ectopic pregnancy

Although imaging is not required to make a diagnosis of appendicitis, it may be helpful if previous tests have been inconclusive and acute appendicitis is still suspected.
  • Ultrasound
    • This is a good first-line imaging investigation for acute appendicitis if radiation is a concern, for example in children and pregnant women
    • It is also a good imaging modality if gynaecological causes are suspected
    • It has a sensitivity of 86% and specificity of 81% in the diagnosis of acute appendicitis
  • CT
    • This may be performed if ultrasound is inconclusive but appendicitis is still suspected based on other clinical findings
    • CT may help to minimise the likelihood of a negative appendicectomy
    • CT has a sensitivity of 94% and specificity of 95% in the diagnosis of acute appendicitis
  • MRI
    • Abdominal MRI is rarely used for the investigation of acute appendicitis
    • It may used in pregnancy

Differential diagnosis

There are several conditions which can present with symptoms and signs similar to those of acute appendicitis. They can be categorised into gynaecological, gastrointestinal and urological disorders.

Many gynaecological disorders can mimic appendicitis and it is important to perform a pregnancy test in any female of child-bearing age. An ultrasound scan is often used to differentiate between appendicitis and gynaecological conditions.
  • Ectopic pregnancy
    • Similarities: both can cause right iliac fossa pain, nausea/vomiting and fever
    • Differences: ectopic pregnancies typically present with a 6-8 week history of amenorrhoea with or without vaginal bleeding and a positive pregnancy test
  • Ovarian torsion
    • Similarities: both can cause right iliac fossa pain and nausea and vomiting
    • Differences: a palpable adnexal mass is felt in 50-70% of cases of ovarian torsion
  • Pelvic inflammatory disease
    • Similarities: both can cause lower abdominal pain, nausea/vomiting and fever
    • Differences: in pelvic inflammatory disease pain is typically bilateral, there is vaginal/cervical discharge and cervical motion tenderness on examination
  • Mittelschmerz (ruptured Graafian follicle)
    • Similarities: both can cause lower abdominal pain
    • Differences: Mittelschmerz does not cause localised pain or nausea/vomiting

Gastrointestinal disorders which share common symptoms with acute appendicitis include:
  • Acute mesenteric adenitis (in children)
    • Similarities: both can cause lower abdominal pain with guarding
    • Differences: mesenteric adenitis typically occurs in children after a viral upper respiratory tract infection and it does not cause localised tenderness
  • Meckel’s diverticulitis
    • Similarities: both can cause periumbilical pain which localises to the right iliac fossa and peritonitis
    • Differences: Meckel's diverticulitis is clinically indistinguishable from acute appendicitis and is often identified when a normal appendix is found during laparoscopic appendicectomy
  • Inflammatory bowel disease (Crohn’s)
    • Similarities: both typically present in young adults and can cause right lower quadrant pain, fever and nausea/vomiting and raised inflammatory markers
    • Differences: Crohn's disease often presents with chronic diarrhoea and there may be a positive family history
  • Acute cholecystitis
    • Similarities: both present with right-sided abdominal pain with or without guarding and raised inflammatory markers
    • Differences: In cholecystitis pain is typically in the right upper quadrant region and there may be a palpable gallbladder

Urological disorders which should be excluded:
  • Testicular torsion
    • Similarities: both can cause abdominal pain and nausea/vomiting and affect children and young adults most commonly
    • Differences: in testicular torsion, there is typically severe testicular pain and testicular oedema
  • Ureteric stones (especially on right side)
    • Similarities: both can cause right-sided abdominal pain and nausea/vomiting
    • Differences: in nephrolithiasis, pain is typically in the flank, colicky in nature and radiates to the groin
  • Urinary tract infection
    • Similarities: both can present with lower abdominal pain and fever
    • Differences: urinary tract infections typically present with dysuria, urgency and frequency and affect older adults more commonly


All patients with suspected acute appendicitis should be admitted to hospital.

Gold-standard for the definitive treatment of acute appendicitis is a laparoscopic appendicectomy.
  • Laparoscopic appendicectomy describes the surgical removal of the appendix
    • Studies have shown that laparoscopic appendicectomy has significant advantages over open appendicectomy including decreased length of hospital stay, lower incidence of surgical wound infection and reduced post-operative pain.
    • However, removal of the appendix laparoscopically can be more technically demanding and requires specialist equipment
    • Once a diagnosis of appendicitis is made, in order to minimise perforation risk, appendicectomy should not be delayed
    • Studies have shown that after 36 hours from symptom onset, the risk of perforation is 16-36% and this increases by 5% for every subsequent 12 hour period
  • Patients should receive prophylactic antibiotics prior to surgery to minimise the risk of post-operative complications
  • The appendix should be sent for histopathology to rule out malignancy (found in 1% of cases of acute appendicitis)
  • Patients with confirmed perforated appendix should be managed with:
    • Urgent appendicectomy
    • Post-operative antibiotics
  • Patients who are unfit for surgery should be managed conservatively with analgesia, IV fluids and IV antibiotics.

In recent years there has been some debate surrounding the use of intravenous antibiotics as an alternative to surgery in uncomplicated appendicitis.
  • A recent Cochrane review analysing appendicectomy versus antibiotic treatment for acute appendicitis concluded that antibiotic therapy alone should not be used as an alternative to surgery in uncomplicated appendicitis.
  • This was due to a readmission rate of 14-35% in the group managed with IV antibiotics alone
  • It concluded that conservative management with IV antibiotics should be reserved for patients who are unfit or decline surgery.


The mortality for acute appendicitis is between 0.1-0.4%. Despite this relatively low risk, there are a number of important complications:
  • Appendiceal perforation
    • This is the most common complication of appendicitis
    • The average rate of perforation at presentation is 16-30%
    • The rates of perforation are higher in elderly patients and young children, likely due to delayed diagnosis
    • Signs of perforation include shock and a tense, distended abdomen with guarding and rigidity
    • Perforation can cause a peri-appendiceal abscess which may be felt as a palpable mass on examination
  • Surgical wound infection
    • The rate of surgical wound infection is lower if a laparoscopic approach is taken rather than open
    • Prophylactic antibiotics reduce the risk
  • Appendicular mass
    • This occurs when omentum and small bowel adheres to the appendix
    • Typically affects patients with a long history of symptoms
    • Presents as a tender mass in the right iliac fossa
  • Appendicular abscess
    • An appendicular abscess may form around a perforated appendix
    • Symptoms include a tender right lower quadrant mass, fever and leucocytosis
    • Appendicular abscesses also occur in 1 in 500 cases post-appendicectomy
    • Most cases require CT or ultrasound-guided drainage and antibiotics