Appendicitis

Contributed by Mr Joe Dawson, specialist registrar in general surgery, Southend University Hospital NHS Trust.

Section 1: Epidemiology and aetiology

Embryological origin
The vermiform (worm-like) appendix is a continuation of the caecum found at the junction of the small and large bowel. During fetal development the appendix fails to elongate with the rest of the colon, resulting in a small, blind-ending tube.

Some evidence suggests that the appendix has an immunological role, the consensus opinion is that it is a vestigial organ, representing the remnants of a larger caecum previously required to accommodate cellulose-digesting bacteria necessary for a herbivorous diet.

CT scan demonstrating pelvic abscess adjacent to rectum

Epidemiology
Acute appendicitis has an incidence of 7-12 per cent in the UK and is the most common abdominal surgical emergency, resulting in 70,000 appendectomies per year. The lower incidence of appendicitis in developing countries may be explained by the high intake of dietary fibre.

Although appendicitis can occur at any age, the peak incidence is between the third and fourth decades of life. Despite appendicitis being more common in males, appendectomy is more commonly performed in females, due to other conditions mimicking appendicitis and the possibility of infertility resulting from perforated appendicitis.

Pathology
Appendicitis, inflammation of the appendix, is thought to result from blockage of the appendiceal lumen. The commonest cause is submucosal lymphoid hyperplasia within the appendix wall (60 per cent). This may account for higher incidence in the young, when the number of lymphoid aggregates within the appendix is greater.

Less common causes of obstruction are faecoliths or faecal stasis (35 per cent), foreign bodies, such as parasitic worms (4 per cent) and tumours of the caecum or appendix (1 per cent).

Luminal blockage results in secondary infection leading to the sequential pathological states that classify the severity of appendicitis: acute, suppurative, gangrenous and perforated.

With the lumen obstructed, continued mucus production leads to increased pressure and stasis within the appendix, leading to bacterial overgrowth.

The mucus develops into pus, further increasing pressure, and distension of the appendix leads to the first symptom of visceral pain in the umbilical region. Continued luminal pressure blocks lymphatic drainage leading to oedema, the hallmark of acute appendicitis. As the engorged appendix rubs against the overlying parietal peritoneum the pain becomes more severe and localises to the right iliac fossa (RIF).

Section 2: Diagnosis

Clinical features
The most important step in managing appendicitis is making an early diagnosis based on history and examination. The strongest predictor of perforation is postponed surgery.1

The principal feature of appendicitis is RIF pain, a symptom common to many conditions (see box below). Although less than 10 per cent of cases of acute abdominal pain seen in primary care will have any surgical cause,2 appendicitis should always be considered. The classic features of appendicitis are present in only half of patients, making accurate and rapid diagnosis challenging in others.

History
Initially a vague central or peri-umbilical abdominal pain is described, followed by a shift and localisation to the RIF after 12-24 hours. Thereafter the pain becomes more intense and is aggravated by movement. Associated symptoms include anorexia and nausea. Diarrhoea or constipation can be present.

Examination
The patient is flushed, lying still, with a dry tongue, foetor oris, low-grade pyrexia (<38 degsC) and a mild tachycardia. Guarding is present with localised peritonism in the RIF over McBurney's point (see box below). Peritonism elicited by deep palpation and sudden release is painful and adds little to the examination. A preferable method is to percuss the anterior abdominal wall.

The base of the appendix is in a constant position, but presentation depends upon the position of the tip, which is variable. The caecum can protect an inflamed retrocaecal appendix from the anterior abdominal wall leading to reduced RIF tenderness and guarding is diminished.

Investigations
Simple tests in primary care are essential to exclude other conditions. These include a temperature (high-grade pyrexia unlikely in appendicitis unless perforated), urinalysis (exclude UTI or colic; haematuria may be present in pelvic appendicitis) and beta-HCG (exclude ruptured ectopic pregnancy). In secondary care the combination of a raised white count and CRP strengthen the diagnosis.

Risk of delayed diagnosis
Despite the incidence of appendicitis in pregnancy being similar to non-pregnant women, increasing gestational age is associated with reduced diagnostic accuracy and increased perforation.3 Presentation can be confused with normal gestational symptoms. The risk of fetal death rises from 4 per cent during uncomplicated appendectomy up to 35 per cent in perforated appendicitis.

In very young children, a lack of history combined with non-specific symptoms frequently leads to late presentation. In addition, an underdeveloped greater omentum can fail to localise any developing sepsis. For these reasons, 75 per cent of young children present with perforation, peritonitis and abscess formation.

Despite the incidence of appendicitis having a second peak around the seventh decade, the diagnosis is often overlooked in the elderly, leading to perforation in 50 per cent of cases. The combination of perforation and diminished physiological reserve results in increased mortality in this age group.

Patients with major mental illness are also at higher risk of delayed diagnosis and subsequent perforation. This is due to patient factors (impaired capacity to recognise or articulate physical illness), systematic failures (difficulty accessing health care) and misdiagnosis.1

Clinical signs in appendicitis
Clinical signDescription
McBurney's pointSurface marking of the base of the appendix lying one third of the way along a line drawn from the anterior superior iliac spine to the umbilicus. Classic position of maximal tenderness.
Rovsing's signPain in RIF elicited by palpating LIF. Generally unreliable.
Psoas signPain in RIF elicited by extending the hip with the knee in full extension or by flexing the hip against resistance. May be useful in retrocaecal appendicitis but generally unreliable.
Obturator signPain in RIF elicited by internally rotating of the leg with the hip and knee flexed. May be useful in pelvic appendicitis but generally unreliable.
Alders signDiminished pain on rolling the patient to the left after eliciting the point of maximum tenderness with the patient supine. Generally unreliable.
Tender rectal examinationTender in pelvic appendicitis and other pelvic pathology (combined with vaginal examination). In men offers little additional diagnostic value when abdominal signs are present


RIF pain
Differential diagnosis of RIF pain

  • Acute cholecystitis
  • Meckel's diverticulitis
  • Intussusception
  • Volvulus
  • Perforated peptic ulcer
  • Pancreatitis
  • Obstruction
  • Malignancy
  • Ectopic pregnancy
  • Ovarian torsion
  • Mittelschmerz (ruptured ovarian follicle)
  • Pelvic inflammatory disease
  • UTI

Section 3: Management

Current treatment
Open appendectomy performed via a small incision in the RIF is the conventional treatment for appendicitis. A macroscopically normal appendix is still removed for two reasons: microscopic inflammation may be present, and to avoid confusion should the patient present in the future with pain and a scar in the RIF.

A negative appendectomy rate of 15-30 per cent has traditionally been accepted due to the morbidity associated with perforation.

Acute appendicitis with adherent omentum at tip

New developments
Attempts have been made to develop evidence-based scoring systems to more accurately diagnose appendicitis (see box).4 However these systems have variable reproducibility, with less sensitivity in females where diagnostic dilemma is highest. A meta-analysis examining the diagnostic value of history, symptoms, signs and tests found that a combination of a strong inflammatory response (raised white cell count and CRP), signs of peritoneal irritation (rigidity, percussion and rebound tenderness) and migration of pain has a high discriminatory and predictive power.6

Imaging
Meta-analysis of imaging modalities have suggested that ultrasound has only a modest ability to make a diagnosis,7 and normal ultrasound does not exclude appendicitis. It does however have a useful role in differentiating gynaecological causes and when an appendix mass or abscess is present.

CT is far more sensitive and specific, but is limited by the cost, radiation dose and availability and is not routinely recommended.7

Laparoscopic surgery
Compared with open surgery, laparoscopic appendectomy is associated with fewer wound infections and post-operative pain, shortened hospital stay and a quicker return to normal activities.8

Some of these advantages are small and of limited clinical relevance. In addition it takes longer, with higher operative costs and a higher incidence of intra-abdominal abscess.8

One of the great advantages of laparoscopy is in women with diagnostic uncertainty, reducing the risk of a negative appendectomy.

Young, female, obese and employed patients seem to benefit the most from laparoscopic appendectomy.

Modified Alvarado Scoring System5

Feature

 Score
Symptoms
  • RIF pain
  • Nausea/vomiting
  • Anorexia

1

1

1

Signs
  • RIF tenderness
  • Fever
  • Rebound

2

1

1

Investigations
  • WCC >10,000
  • Left shift neutrophils

2

1

Surgery is recommended with a score of >7

Section 4: Prognosis and follow-up

Follow-up
Most patients are discharged from hospital within 48 hours after surgery and resume normal activities within a few weeks.

Routine outpatient review is not common practice. Histological examination of appendectomy specimens reveal incidental tumours in 1 per cent of cases, with the majority of these being low-grade carcinoid tumours.

Although they do have metastatic potential most carcinoid tumours less than 10mm at the time of diagnosis are adequately treated by appendectomy and are associated with a good long-term outcome. A right hemi-colectomy is considered for larger tumours. Rarer appendiceal tumours such as adenocarcominoma have a worse prognosis.

Perforated appendicitis causing inflammatory appendix mass

Complications
Patients presenting with a longer history may have developed an inflammatory mass involving the appendix, caecum, omentum and small bowel. Clinical signs include a palpable tender mass in the RIF. Initial treatment for a mass is conservative, consisting of antibiotics and IV fluids. It either resolves or develops into an appendix abscess.

Patients with appendix abscess present later with a swinging pyrexia. Although the abscess may be palpable, common sites are the pelvis, and rectal and vaginal examination is useful. Treatment consists of percutaneous or open drainage. Following conservative treatment of an appendix mass or abscess, interval appendectomy may be considered.

Despite improved asepsis and surgical techniques, postoperative infections still occur in up to 40 per cent of all appendectomies.9 The choice of antibiotic for a wound infection may be guided by swab results taken at surgery, and should cover the predominant gram-negative coliforms associated with acute appendicitis.

Post-operative abscess
An intra-abdominal abscess should be considered in patients presenting with non-specific symptoms or signs of infection following appendectomy and should be referred to the surgical team for diagnosis and percutaneous or open drainage.

Grumbling appendix
The condition of a 'grumbling appendix', or chronic appendicitis, is contentious. Some patients with chronic, intermittent RIF pain may be offered elective appendectomy, but only when all other diagnoses have been excluded.

References

1. Tsay J, Lee C, Hsu Y et al. Disparities in appendicitis rupture rate among mentally ill patients. BMC Public Health 2007; 7(147): 331.

2. de Dombal F. Diagnosis of Acute Abdominal Pain - 2nd Edition. 1991 Churchill Livingston, UK.

3. Brown J, Wilson C, Coleman S, Joypaul B. Appendicitis in pregnancy: an ongoing diagnostic dilemma. Colorectal Dis 2008 (May 29. Epub ahead of print).

4. Liu J, Wyatt J, Deeks J et al. Systematic reviews of clinical decision tools for acute abdominal pain. Health Technology Assessment 2006; 10(47) http://www.hta.ac.uk/1130

5. Kalan M, Talbot D, Cunliffe W, Rich A. Evaluation of the modified Alvarado score in the diagnosis of acute appendicitis: a prospective study. Ann R Coll Surg Engl 1994; 76(6): 418-9.

6. Andersson R. Meta-analysis of the clinical and laboratory diagnosis of appendicitis. Br J Surg 2004; 91: 28-37.

7. Weston A, Jackson T, Blamey S. Diagnosis of appendicitis in adults by ultrasonography or computed tomography: a systematic review and meta-analysis. Int J Technol Assess Health Care 2005; 21(3): 368-79.

8. Sauerland S, Lefering R, Neugebauer E. Laparoscopic versus open surgery for suspected appendicitis. Cochrane Database Syst Rev 2004, Issue 4. Art. No: CD001546. DOI: 10.1002/14651858.CD001546.pub2

9. Andersen B, Kallehave F, Andersen H. Antibiotics versus placebo for prevention of postoperative infection after appendectomy. Cochrane Database Syst Rev 2005, Issue 3. Art. No: CD001439. DOI: 10.1002/14651858.CD001439.pub2

Further resources

  • Humes D, Simpson J. Acute appendicitis - Clinical Review. BMJ 2006; 333: 530-4.
  • Simpson J, Scholefield J. Acute Appendicitis. Surgery (The Medicine Publishing Company Ltd) 2008; 26(3): 108-112.
  • Doyle VJ, Bateman AC. Pathology of appendiceal tumours. Surgery (The Medicine Publishing Company Ltd) 2007; 25(9): 363-7.

For an archive of all GP clinical reviews visit www.healthcarerepublic.com/clinical/GP

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