Appendicitis

What is appendicitis?

Acute appendicitis describes sudden inflammation of the appendix, usually initiated by obstruction of the lumen. This results in invasion of the appendix wall by gut flora, and it becomes inflamed and infected. If the appendix then ruptures, infected and faecal matter escape into the peritoneal cavity, producing life-threatening peritonitis. Alternatively, particularly if perforation or gangrene occurs after 24 hours or more, the inflamed surfaces may become stuck together first so that the peritonitis is trapped and localised. Sometimes the inflamed appendix becomes surrounded by omentum which adheres and localises the infection more effectively, forming an appendix mass or appendix abscess.¹

How common is appendicitis? (Epidemiology)

• Appendicitis is the most common cause of an acute abdomen in the UK.

• About 10% of the population will develop acute appendicitis.²

• Appendicitis is most common between the ages of 10 and 20 years but can occur at any age.³

• Appendicitis is more common in men than in women.³

• A normal appendix is removed at 10-20% of appendicectomies.²

Appendicitis symptoms

Classic symptoms often do not appear in young children, in pregnant women and in the elderly, and the diagnosis is particularly easy to miss in these age groups. The classical presentation consists of:

• Pain:
  

  • Early periumbilical pain moves, after hours or sometimes days, to the right iliac fossa (RIF) as the peritoneum becomes involved. Pain which wakes the patient or keeps a child awake is significant.

  • Movement and coughing aggravate the pain. The patient may lie still with shallow breathing. Deep breathing and coughing hurt.

• Nausea, vomiting, anorexia. The patient is usually constipated or simply does not want to have the bowels open, but may have diarrhoea. Rapidly progressive cases may have recurrent vomiting without fever and diarrhoea. This may be marked in post-ileal appendix (which is rare).

• Temperature and pulse are initially normal. Low-grade pyrexia then develops.

• A rising pulse rate may be an indication of peritonitis.

• Localised tenderness, guarding and rebound tenderness develop in the RIF.

• Rovsing's sign may be positive: palpation of the left lower quadrant increases the pain felt in the right lower quadrant. This pressure stretches the entire peritoneal lining, and so causes pain in any location where the peritoneum is irritating the muscle.

• RIF peritonism can also be demonstrated by percussion tenderness or rebound tenderness.

• Other methods to demonstrate an inflamed appendix include: the psoas test (extend the hip and abduct the thigh with the patient on the left side) and the obturator test (flex and internally rotate the right hip).

• A retrocaecal or pelvic appendix may be missed. Rectal examination may reveal localised tenderness as the only sign of an inflamed retrocaecal or pelvic appendix.

• Stage of illusion: just after perforation, a child may sit up in bed apparently better. A rising pulse rate may be the only indication of perforation, before the obvious signs of peritonitis develop.

Atypical presentations

• Pain may be atypical due to unusual appendix positioning. The position of the appendix can vary considerably in non-pregnant individuals. A fully mobile caecum and ascending colon are rarely present, although some degree of caecal mobility is found in 10-20% of patients at post-mortem, which may have significance for the presentation of appendicitis.^{4 5} Pain, therefore, may be predominantly left-sided pain in the upper and/or lower quadrants, suprapubic pain, generalised abdominal pain, low back pain or rectal pain.

• This makes it important to consider the appendix as a differential diagnosis of all acute abdominal pain, and to identify the caecum by imaging in patients with suspicion of acute appendicitis and atypical pain.

• Pregnancy: the appendix is usually pushed upwards on the abdomen by the developing uterus in the second trimester of pregnancy. Pain and tenderness may be higher in pregnant women, although RIF symptoms are still the main presentation.

• Infants may present with watery diarrhoea and vomiting.

• Young children may show only vague abdominal pain and anorexia.

• Elderly patients may present with confusion without pain. They may also present with shock. Progression can be very rapid.

Scoring systems

• The diagnosis of acute appendicitis can be made on clinical history and examination alone in some cases; however, this is sometimes challenging.

• Scoring systems have been shown to be useful in determining the need for further investigation and treatment for acute appendicitis.

• A 2017 systematic review concluded that the Appendicitis Inflammatory Response (AIR) score appeared to perform best, with a sensitivity of 92% and a specificity of 63%.⁶ AIR scores the following indicators:⁷

  • Vomiting (scores 1).

  • RIF pain (1).

  • Rebound tenderness (light=1, medium=2, strong=3).

  • Temperature ≥38.5°C (1).

  • Percentage of polymorphonuclear leukocytes in white cell count (70-84%=1, ≥85%=2).

  • White cell count (10.0-14.9 x10⁹/L=1, ≥15 x10⁹/L=2).

  • C-reactive protein level (10-49 mg/L=1, ≥50 mg/L=2).

  • A score of 0-4 makes appendicitis unlikely; 5-8 should trigger observation with serial re-examination, imaging, or diagnostic laparoscopy dependent on local practice; and scores of 9-12 should trigger surgical exploration.

• The Adult Appendicitis Score also appears to perform well.^{8 9}

• A well-known scoring system is the Alvarado score, which has been extensively validated. Whilst this is sufficiently sensitive to rule out acute appendicitis, it is less specific and therefore not useful in positively confirming appendicitis if there is clinical suspicion.⁹

• Other scoring systems include the RIPASA score, the Pediatric Appendicitis Score and the Pediatric Appendicitis Laboratory Score - the latter two for children.⁹

• In children, the Alvarado and Pediatric Appendicitis Scores are useful for excluding acute appendicitis if low, but high scores are not specific and should not be relied upon as definitive evidence of appendicitis alone.⁹

Differential diagnosis

Other causes of abdominal pain

Gastrointestinal
Gastrointestinal obstruction, constipation, intussusception, strangulated hernia, acute cholecystitis, perforated peptic ulcer, mesenteric adenitis, Meckel's diverticulitis, Crohn's disease, diverticulitis, pancreatitis, rectus sheath haematoma, gastroenteritis.

Urological
Testicular torsion, renal calculi, urinary tract infection.

Gynaecological
Ectopic pregnancy, torsion or rupture of an ovarian cyst, pelvic inflammatory disease.

Others
Diabetic ketoacidosis, pneumonia, porphyria, adverse effects from immune modulation therapies (eg, panniculitis in the abdomen at the left iliac fossa, associated with beta-interferon injection).¹⁰

Other causes of RIF mass^{11 12}

These include: Crohn's disease, carcinoma of colon, mucocele of the gallbladder, psoas abscess, pelvic kidney, ovarian cyst.

Investigations

Whilst appendicitis is traditionally thought of as a clinical diagnosis (see the separate Abdominal Examination article), it is increasingly recognised that clinical assessement alone can be unreliable, especially in groups of people who tend to have atypical presentations - such as pregnant women, older adults and infants. Investigations are generally requested to exclude other differential diagnoses; they are also particularly useful in intermediate-risk patients - ie those where the suspicion of appendicitis is moderate, but not high enough to proceed directly to surgery. These include:

• Urinalysis to exclude urinary tract infection.

• Pregnancy test to exclude ectopic pregnancy (essential in women with any possibility of pregnancy).

• FBC: there is usually a mild leukocytosis, but a normal white cell count does not exclude appendicitis.

• Raised inflammatory markers: CRP may be raised, but a normal level does not exclude a diagnosis of appendicitis.

• Imaging is a useful diagnostic tool in suspected appendicitis, and its use is increasing. It is most useful in patients where the diagnosis is indeterminate.¹³

  • Ultrasound is useful, and tends to be preferred in children, young people, and pregnant patients, due to the radiation risk associated with CT. It is also better at diagnosing gynaecological causes of right iliac fossa pain.¹³ However, it may be difficult to obtain diagnostic images in patients with obesity. Confidently identifying a normal appendix, and therefore, ruling out appendicitis, can also be challenging.

  • CT scanning is more sensitive and specific than ultrasound when diagnosing acute appendicitis.³ It is very widely used in the USA (used in 86% of patients),¹⁴ which seems to have led to their lower rate of negative appendicectomies.^{15 16} This approach however is controversial due to the risk of radiation exposure from CT imaging, particularly in children and younger adults.

  • Low-dose CT imaging may provide equivalent diagnostic information to standard CT, with a much lower radiation dose.⁹

  • The most useful predictors of acute appendicitis on CT are enlarged appendix, appendiceal wall thickening, peri-appendiceal fat stranding, and appendiceal wall enhancement.¹⁷

  • MRI is usually reserved for use in pregnant women as a second-line investigation, after a non-diagnostic ultrasound.¹⁸

• Diagnostic laparoscopy may be considered.

Appendicitis treatment

• All suspected cases should be admitted to hospital.

• Appendicectomy is traditionally considered to be the 'gold standard' treatment. This is often done as a laparoscopic procedure.¹⁸

• Spontaneous resolution of early uncomplicated appendicitis can occur. Some limited data suggest that treatment of uncomplicated appendicitis with supportive care only (no antibiotics or surgery) may be an acceptable option;^{19 20} however, more data are required to confirm this. Currently, surgical intervention is the mainstay of treatment.

• Medical treatment with antibiotics may be an alternative to surgery. This is an area of much research and controversy, especially in recent years. Some trial data have been encouraging in supporting antibiotic treatment as a safe and effective treatment for appendicitis. For example, a 2016 meta-analysis found that antibiotic treatment may be associated with a lower risk of complications than surgery.²¹ However, a 2022 updated meta-analysis, incorporating data from larger trials, found no difference in complication rates between antibiotic-only and surgical treatment, and also that antibiotic treatment was less effective than surgery, and associated with higher rates of readmission.²²

• A key drawback of antibiotic therapy, compared to surgery, is that surgery is a 'one-time only' procedure, whereas antibiotic treatment has a significant recurrence rate for appendicitis (up to 39% at five years).⁹

• Concerns around aerosol-generating procedures during surgery in the early months of the COVID-19 pandemic lead to antibiotic-first treatment being used widely in the UK, at least for a short period.²³

• The 2020 World Society of Emergency Surgery guidelines suggest that non-operative management with antibiotics may be an acceptable treatment option for a carefully selected cohort of patients with uncomplicated acute appendicitis with absence of appendicolith - in the context of shared-decision making with the patient, particularly regarding the risk of recurrence.⁹

• In cases of diagnostic doubt a period of 'active observation' can be useful.

• Intravenous fluids and sufficient analgesia are also required.

• Pre-operative antibiotics are associated with a reduction in surgical site infections. Postoperative antibiotics are indicated in complicated appendicitis, but are not necessary in cases of uncomplicated appendicitis.⁹

• There is considerable evidence for laparoscopic appendicectomy over an open appendicectomy approach. Many studies suggest the laparoscopic approach leads to a reduced hospital stay and more rapid return to normal activity, both in uncomplicated and in complicated appendicitis (including cases with perforation).^{24 9 18}

Complications

• Perforation: the average rate of perforation at presentation is between 16% and 30% (significantly higher in elderly people and young children).³

• Wound infection: rates of wound infection vary from <5% in simple appendicitis to 20% in cases with perforation and gangrene. Perioperative antibiotics have been shown to decrease the rates of postoperative wound infections.¹

• Appendix mass:
  

  • Omentum and small bowel adhere to the appendix.

  • Usually presents with a fever and a palpable mass.

  • Initial treatment is usually conservative with fluids, analgesia and antibiotics; surgical intervention may be technically demanding and involve a more extensive colonic resection. Urgent surgical intervention may be required if the mass enlarges or the patient's condition deteriorates.

  • This conservative management approach is controversial. Traditional management has been conservative, with interval appendicectomy performed weeks after the mass has resolved. This remains the most common approach at many centres in the world. Recently, an increasing number of studies have challenged this approach,^{25 26} and some authors advocate against the routine use of interval appendicectomy, citing low recurrence rates after conservative management.²⁷

• Appendix abscess: can be shown by ultrasound or CT scan; initial treatment is usually by percutaneous or open drainage (open drainage also enables appendicectomy) - but, again, there is controversy and a lack of a clear 'best option', with some surgeons preferring initial conservative management (fluids and antibiotics) with appendicectomy after delay.²⁸

• Other acute complications include pelvic abscess, subphrenic abscess, paralytic ileus and septicaemia.

• Long-term complications: adhesions may cause intestinal obstruction but this is uncommon.

• Maternal mortality is very low in acute appendicitis in pregnancy but increases to 4% with perforation in late pregnancy. Fetal mortality is less than 1.5% but increases to 20-35% in cases of perforation.³

Prognosis

• Appendicectomy is relatively safe with a mortality rate for non-perforated appendicitis of 0.8 per 1,000 and mortality after perforation of 5.1 per 1,000.³

• The mortality rate is more than 20% in patients older than 70 years. More subtle symptoms and a more virulent pathological course mean the disease can progress rapidly. This leads to delayed diagnosis and hospitalisation, and delayed treatment. The high incidence of comorbidities and the wide range of differential diagnostic possibilities in this age group are also factors.²⁹

Dr Mary Lowth is an author or the original author of this leaflet.