Appendicitis

Authors: Janet Skinner / Editor: Janet Skinner / Reviewer: Michael Perry, Amanda King / Codes: CAP1, HAP1 / Published: 21/04/2020 / Review Date: 21/04/2023

Appendicitis is one of the commonest surgical problems that present to emergency departments (ED). It accounts for around 40 000 admissions per year in England, mainly in patients between the ages of 15 and 25 years of age [1]. Adults in the Western world have around a 6-8% chance of developing appendicitis in their lives, although the incidence seems to be falling somewhat in recent years [1]. Appendicitis is less common in the developing world.

The mortality of appendicitis rises from 0.8 per 1000 cases to 5.1 per 1000 cases if the appendix perforates [1]. Importantly, up to 10% of appendicitis cases in the US are not picked up on first clinical assessment [2].

Learning bite

Patients are at much higher risk of significant morbidity and mortality if their appendix perforates.

Appendicitis has a wide differential diagnosis including gastro-intestinal, gynaecological and urological causes. Differential diagnoses are shown below:

Table 1: Differential diagnosis of appendicitis

Gastro-intestinal

Gynaecological

Urological

Terminal ileitis Ruptured ovarian cyst Renal colic
Mesenteric adenitis Ectopic pregnancy Urinary tract infection
Meckels diverticulitis Pelvic inflammatory disease Pyelonephritis
Diverticulitis Ovarian torsion
Acute cholecystitis
Gastroenteritis
Bowel obstruction
Non-specific abdominal pain

History

The classical history in acute appendicitis is that of initial colicky central abdominal pain that moves after 6-12 hours to the right iliac fossa (RIF) where it is constant in nature [1]. This classic history is only present in half of the patients that present to the ED with appendicitis [1].

Other common symptoms include anorexia (which tends to be present in 80% of patients with appendicitis), nausea, vomiting (which starts after the pain) and constipation or diarrhoea [2]. Appendicitis often presents with an atypical history, particularly in the elderly, children and pregnant patients, and can make these very difficult diagnostic groups, where the diagnosis may be made late and the risk of perforation is higher [4].

Why does the pain of appendicitis move from the periumbilical area to the RIF?

Remember that the appendix is innervated by the autonomic nervous supply to the mid-gut. Inflammation in the appendix activates afferent sympathetic fibres, which enter the spinal cord at T10 resulting in referred colicky pain to the periumbilical area [3]. Eventually inflammation in the appendix will irritate the surrounding parietal peritoneum, which is innervated by the intercostal nerves resulting in constant local pain in the RIF.

Remember that visceral pain is normally vague, colicky and felt in the midline.

Somatic pain is more constant, and felt at the local site [3,5].

Learning bite

The classic migrating of pain of appendicitis has a sensitivity and specificity of around 80% [3,5].

Examination

The patient can looked flushed, dehydrated and have a furred dry tongue with bad breath. They may also have a fever and slight tachycardia. Patients with perforated appendicitis are more likely to have a high temperature (>38.5) than those with uncomplicated appendicitis.

Abdominal examination

Patients are in pain, want to lie still and may have tenderness in the RIF, maximal over McBurney’s point which lies one-third of the way along an imaginary line from the anterior superior iliac spine to the umbilicus, and indicates where the inflamed appendix normally lies.

What are the signs of localised peritonism in a patient with suspected appendicitis?

  • Direct tenderness – press in RIF and patient experiences pain
  • Guarding – due to voluntary or involuntary contraction of abdominal muscles
  • Rigidity – due to reflex spasm of abdominal wall muscles
  • Rebound – press enough to depress peritoneum in the RIF for 30s, suddenly remove hand, patient experiences rebound pain
  • Rovsings sign – press deeply in the LIF for 30s, release suddenly, patient experiences rebound tenderness in RIF
  • Psoas sign – ask patient to lift flexed thigh against your hand placed just above the knee, patient experiences pain in RIF (4,5)

How do you elicit signs of localised peritonism in a humane way?

While these signs are useful in making a diagnosis a patient in pain will not thank you for trying to elicit them. A kinder way to detect signs of localised peritonism can be

  • Ask the patient to ‘blow their abdomen out fat’ and then ‘suck it in thin’
  • Ask the patient to cough gently
  • Percuss gently over the RIF to elicit guarding and rigidity

Patients may also be tender on digital rectal examination. There is evidence to suggest that the finding of a painful rectal exam is of little benefit with positive and negative predictive values of 0.44 and 0.54 respectively [6]. Certainly multiple rectal examinations should be avoided in patients with suspected appendicitis.

Learning bite

Appendicitis largely remains a clinical diagnosis based upon piecing together the history and examination.

Risk Assessment

There are currently no risk assessment tools widely used in practice that predict morbidity and mortality in patients who present with appendicitis. What is known is that patients with a perforated appendix are at higher risk of complications and death, therefore it is vital to try and make the diagnosis in a timely fashion and to recognise that children, elderly patients and pregnant patients are at higher risk because of diagnostic difficulties.

Learning bite

Unnecessary delays to theatre can lead to an increased rate of perforation of the appendix and worse outcomes in patients with appendicitis.

Urinalysis-note up to 30% of patients with appendicitis will have an abnormal urinalysis; send urine for urgent gram stain if in doubt (2)

Urinary beta hCG- to exclude ectopic pregnancy in any female of child bearing age

Full blood count 80-90% of patients with appendicitis will have a raised white cell count (>10 x 105). While helpful, white cell counts will also be raised in other causes of RIF pain and cannot rule in or out the diagnosis (2,7)

C-reactive protein- shows specificity and sensitivities of around 50-60%. Again, CRP is helpful but fairly non-specific but is more useful if interpreted in combination with the WCC (2)

Plain abdominal x-ray there is no role for plain films in patients with RIF pain, unless to look for another diagnosis (such as obstruction)

Learning bite

90% of patients with appendicitis will have a raised WCC/CRP.

Clinical Scoring Tools

The most commonly used clinical tool is the ALVARADO score. It was designed originally for use in pregnant women but has now been validated across all patient groups. It has been found to have a sensitivity of about 72%, and should be used in conjunction with clinical judgement, rather than as an isolated diagnostic tool. A score of 5-6 is considered to be highly suggestive of appendicitis.

Predicting the likelihood of appendicitis based on clinical and laboratory findings

A meta-analysis of 24 studies looked at the use of clinical and laboratory predictors of appendicitis in terms of their predictive and discriminatory values [10]. Receiver Operator Curves (ROC) were calculated to assess discriminatory power. The ROC is the proportion of true positives (patients with appendicitis) against true negatives (patients without appendicitis) for each value of the test. A value of 0.5 shows no discrimination and a value of 1.0 shows complete discrimination.

Positive likelihood ratios (+LR) were calculated to describe predictive value of the findings. A+LR is the likelihood that a given test result would be present in a patient with appendicitis. A positive likelihood ratio of >1 suggests that the post-test probability of appendicitis is greater that the pre-test probability.

The two tables below the variables with the highest +LR and ROC values from the meta-analysis [10].

Variable
Positive Likelihood Ratio
P value
Pain migration
2.06 (1.63, 2.60)
<0.001
CRP raised
2.39 (1.67, 3.41)
0.001
Guarding
2.48 (1.60, 3.84)
0.015
Percussion tenderness
2.86 (1.95, 4.21)
0.820
Rigidity
2.96 (2.43, 3.59)
<0.001
White cell count raised
3.47 (1.55, 7.77)
0.008
WCC and CRP raised
23.32 (6.87, 84.79)
None given
Guarding/rebound and WCC raised
11.34 (6.65, 19.56)
None given

Andersson et al (10) . Discriminatory power of clinical and laboratory variables (ROC 0.65 or more in increasing order)

Variable
Pooled ROC area
P value
Migration of pain
0.68
<0.001
Guarding
0.68
<0.001
Rebound
0.70
<0.001
Percussion
0.70
0.793
CRP level
0.75
<0.001
WCC
0.77
0.171
Guarding and WCC raised
0.84
None given
WCC and CRP raised
0.96
None given

While each of these variables independently has a fairly weak predictive and discriminatory value they are of most use in combination e.g. signs of peritonism and a raised WCC attain high +LRs and ROC values (10).

Learning Bite

Migration of pain, RIF rigidity and guarding with raised inflammatory markers in combination strongly suggest appendicitis (10).

Imaging

Ultrasound Scan

Graded compression ultrasound scan (USS) has been widely used to look for appendicitis in patients with RIF pain. It has an overall accuracy of about 90% (sensitivity 84% and specificity 88%), but is very operator dependent [7,11-12]. A USS can rule in appendicitis but cannot rule it out, i.e. in the presence of a normal scan the patient will still need to be closely observed.

USS is of particular value in trying to identify other pathologies, especially in women of child-bearing age, when the diagnosis may be unclear. It is also of benefit in patients with atypical signs, such as the elderly, children or pregnant patients.

CT

CT has a greater overall accuracy of 94% (sensitivity 94%, specificity 95%) in diagnosing appendicitis compared to USS [12-14]. However, CT is costly, may not be readily available and can result in significant radiation exposure to patients. Studies that have shown improved accuracy of CT over USS predominantly utilised helical CT without contrast [13]. Similarly to USS, CT can rule in but not rule out appendicitis. CT may be better at identifying other pathologies than USS.

If a patient is felt to have a high likelihood of appendicitis then unnecessary imaging should not delay theatre. Remember the mortality and morbidity in appendicitis is higher if the appendix perforates.

Learning bite

Helical CT without contrast is the investigation of choice in patients in whom there are equivocal findings or the diagnosis is not clear.

Diagnostic difficulties

96% of patients will have RIF pain however, atypical pain and diagnostic difficulties are common in the following groups (2)

Group
Difficulty
Children
Atypical symptoms and signs can lead to late presentation
Elderly
Atypical symptoms and signs can lead to late presentation and 3x increased perforation rate
Pregnant patients
Abnormal position of the appendix due to pregnant uterus can cause atypical signs, perforation associated with foetal mortality
Abnormal positioning of the appendix
Atypical site of pain, e.g. with pelvic appendix
Women of child-bearing age
Extensive differential diagnosis including tubo-ovarian pathologies, higher rates of negative appendicectomies

Learning Bite

Maintaining a high index of suspicion in these diagnostic groups may help to prevent missing the diagnosis of appendicitis.

1) Resuscitate – if dehydrated or signs of sepsis

  • Oxygen (high flow, non-rebreather mask)
  • Intravenous access x2
  • IV normal saline 1-2 litres then reassess
  • Give immediate antibiotics if patient has signs of septicaemia or generalised peritonitis (cephalosporin and metronidazole)

2) Analgesia

  • Morphine IV titrated to effect with IV anti-emetic.
  • A Cochrane review states that there is no evidence that opiates mask the signs of peritonism or lead to a delay in diagnosis. Analgesia should never be withheld until the patient has seen the surgeon (15)

3) Keep nil by mouth

4) Involve surgical team

A Cochrane review recommends that once the decision to take the patient to theatre has been made then broad spectrum IV antibiotics (cephalosporin and metronidazole) should be given as they decrease the post-operative rate of wound infection and abscess formation (16).

5) Appendicetomy

Approach to patients with RIF pain
Approach to patients with RIF pain

Learning Bite

Low risk patients who are discharged home need clear advice to return to ED should their symptoms recur.

Surgical Approaches to Management

Surgeons must weigh up the risks and benefits of appendicetomy in patients with RIF pain. Negative appendicetomy rates are often in the region of 10-20% and it is important to try and keep this rate low [1,12], while trying to avoid the risks of perforation with its increase in mortality. Negative appendicetomies have been shown to be associated with the female sex, low WCCs, low pulse and age <21 years [17].

A recent study has shown a reduction in the negative appendicectomy rate from 16.3% to 7.65% in a centre in the US where all patients got a CT before theatre [18]. Serial clinical examinations performed by a senior surgeon are still invaluable in deciding whether or not a patient with equivocal findings requires theatre for appendicectomy. This watchful waiting approach is often advocated for by senior surgeons in patients with an uncertain diagnosis, though has not been extensively researched.

Further Surgical Approaches to Management

The most common surgical approach for uncomplicated appendicitis is a laparoscopic appendicectomy, proven to have reduced rates of post-operative pain and length of hospital stay when compared to older open approaches, which are still used for more complicated cases.

A diagnostic laparoscopy may be used in patients whereby the diagnosis remains uncertain (clinically or on imaging), but pain persists and a diagnosis is deemed necessary. They may be performed in conjunction with gynaecology input as there is a high crossover of symptoms in women of child-bearing age.

Isolated appendiceal masses or abscesses without evidence or risk of perforation may be treated conservatively with IV antibiotics at a later date.

Learning bite

A Cochrane review has found the laparoscopic approach to have diagnostic and ‘therapeutic advantages’.

Summary Approach to Patients with RIF pain

Approach to assessment and management of patients with RIF pain is summarised in the flow chart below. This relies heavily on overall clinical judgement. A patient in whom pain has settled and inflammatory markers are normal is unlikely to have appendicitis and can often be safely discharged if no other pathology is apparent.

Learning bite

Low-risk patients who are discharged home need clear advice to return to the ED should their symptoms recur.

Key Learning Points

  • While the mortality from appendicitis is low it increases approximately ten times if the appendix perforates
  • Perforation of the appendix occurs in up to 30% of cases of appendicitis
  • The classic history of pain migrating to the RIF is only present in around 50% of cases of appendicitis
  • The combination of migration of pain with RIF rigidity and guarding strongly suggests appendicitis and despite advances in investigations remains the mainstay in making a diagnosis (grade 1c, B recommendation)
  • A raised WCC and CRP is present in around 90% of patients with appendicitis, although may be raised also in other causes of abdominal pain (grade 1b, A recommendation)
  • In a patient with clinically suspected appendicitis unnecessary imaging should not delay theatre (grade 4, C recommendation)
  • Helical CT is the investigation of choice in patients with equivocal findings, although like USS, it cannot rule out appendicitis (grade 2b recommendation B)
  • Analgesia should never be withheld as there is no evidence that opiates mask the signs of peritonism (grade 1b, A recommendation)
  • Broad-spectrum intravenous antibiotics should be administered as soon as a decision to take the patient to theatre has been made (grade 1a, A recommendation)
  • Patients who are deemed to be at low risk of appendicitis may be discharged home with clear advice to return if their symptoms recur (grade 5, D recommendation)
  • Laparoscopic appendicectomy results in less post-operative pain but more deep infections (grade 1b, A recommendation)
  • A positive urinalysis does not rule out appendicitis as 30-40% of patients will have an abnormal urinalysis
  • Failure to perform a urinary pregnancy test in female patients with abdominal pain can lead to failure to diagnose an ectopic pregnancy with potentially catastrophic consequences
  • An over-reliance on normal blood tests can result in the diagnosis of appendicitis being missed
  • Remember pregnant patients still get appendicitis and may have atypical findings
  • Atypical presentations and late diagnoses are common in the elderly and children
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