Appendicitis

Introduction

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Appendicitis is a syndrome characterized by inflammation of the inner lining of the vermiform appendix that spreads to its other parts. Despite diagnostic and therapeutic advancement in medicine, appendicitis remains a clinical emergency and is one of the more common causes of acute abdominal pain.

Appendicitis remains the commonest cause of acute abdominal pain requiring surgical intervention, even though there has been a steady decline in incidence in industrialized countries, as measured by appendicectomy rates. The peak incidence is in the second and third decades of life. There is a male preponderance (male: female ratio of 1.4.1), with an overall incidence of around 1.9 per 1000 persons per year. Diagnostic delay is more common in children, women of childbearing age and the elderly.

Early diagnosis is essential to avoid the risk of appendiceal perforation leading to intra-abdominal sepsis, abscess formation and/or generalized peritonitis.

1.    Presentation

Appendicitis is a clinical diagnosis, but the clinical presentation may be atypical or equivocal, requiring a period of active observation or recourse to specialized imaging to confirm the suspicion. When evaluating any patient with acute abdominal pain in the emergency department (ED), one of the focused questions that has to be asked is whether the presentation could be due to appendicitis.

1.1    History

The classic presentation of acute appendicitis is with upper midline or periumbilical pain (70%), which represents visceral mid-gut pain due to appendiceal distension. This progresses over a period of 12–24 hours to right lower quadrant pain (50%), which represents somatic pain caused by localized irritation of the parietal peritoneum.

The migratory pattern of the pain is the most characteristic symptom of appendicitis. Pain is associated with nausea, anorexia (often a prominent feature) and vomiting. Low-grade fever—typically 37.5–38.0^oC—may be present. Once pain localizes in the right lower quadrant, it becomes persistent, is aggravated by movement, deep inspiration and coughing, and tends to progress in severity. Pelvic appendicitis may present with irritative urinary symptoms (frequency of urination and dysuria) or with diarrhoea.

Localization of pain may, however, occur in atypical locations, such as the right upper quadrant or right flank with a retrocaecal appendix (the most common atypical location), or the left lower quadrant with a pelvic appendix or in the presence of situs inversus. Right upper quadrant pain may also be seen in the uncommon event that acute appendicitis complicates pregnancy (on an average one per every 1000 pregnancies).

Symptoms continuing longer than 72 hours make the diagnosis of appendicitis unlikely unless a mass has developed.

1.2    Examination

Examination findings vary according to the stage of evolution. Vital signs may be normal, but a mild tachycardia is usual along with low-grade fever. There may be some facial flushing, fetor oris and a dry, coated tongue.

Typically, there is localized tenderness in the right lower quadrant, classically maximal at McBurney’s point (two-thirds of the way from the umbilicus to the anterior superior iliac spine). This is accompanied by reduction in respiratory movement and by involuntary muscle rigidity (guarding).

Rigidity may be different to elicit in the obese, the elderly, children, and in the presence of atypical locations. Attempted demonstration of rebound tenderness is unkind. The same information can be obtained by noting aggravation of pain by deep inspiration or forced expiration (drawing in or blowing out the abdominal wall), with coughing, or by percussion of the anterior abdominal wall. Right lower quadrant pain may be provoked by pressure on the left lower quadrant (Rovsing’s sign), and there may be accompanying hyperaesthesia of the overlying skin (Sherren’s sign).

Unfortunately, the classic constellation of symptoms and signs is seen in only 50–70% of patients with acute appendicitis. Ancillary clinical signs may be of value in arriving at a diagnosis in patients with atypical symptoms, usually related to atypical locations of the tip.

Psoas muscle irritation, caused by a retocaecal appendix, may be associated with a flexion deformity of the right hip. A positive psoas sign refers to pain with, and resistance to, passive extension of the right hip with the patient in the left lateral position. This has a high specificity but a low sensitivity. Irritation of the obturator internus muscle, caused by a pelvic appendix, may be associated with a positive obturator sign (pain on passive internal rotation of the flexed right hip). An abdominal mass may be palpable in 10–15% of cases. This represents inflamed omentum and adherent bowel loops in the presence of appendiceal perforation.

In most cases, rectal examination in patients with suspected appendicitis is of little value and does not alter management. It may be helpful when the diagnosis is in doubt, particularly in the elderly, when tenderness may be elicited in the right lateral wall of the rectum. Rectal examination may also help diagnose a pelvic abscess in the presence of a ruptured pelvic appendix.

Perforation of the appendix should be suspected in the presence of symptoms of over 24 hours’ duration, a temperature higher than 38^oC, and possibly a white cell count > 15 000 cells/mm.

2.    Differential Diagnosis

Appendicitis can mimic most acute abdominal conditions and should be considered in any patient with acute symptoms referable to the abdomen. There are a wide range of conditions that may resemble appendicitis (see Table X ).

On occasion the diagnosis of appendicitis may only be confirmed at surgery or laparoscopy; however, there is a 10–20% negative laparotomy rate associated with a preoperative diagnosis of appendicitis. Diagnostic delay can be associated with perforation, progression to abscess formation or to generalized peritonitis. These complications can contribute to wound infection, septicaemia and death.

3.    Investigation

3.1    Urinalysis

A urine dipstick examination should be performed in all patients to exclude urinary tract infection, but pyuria and microscopic haematuria can coexist with appendicitis. Qualitative β-hCG testing should be performed in all women of childbearing age in order to exclude pregnancy and the possibility of ectopic gestation.

3.2    Blood Tests

The white count (WCC) lacks sufficient sensitivity and specificity for the diagnosis of appendicitis. A raised white cell count can also be seen with other causes of an acute surgical abdomen. A raised white cell count is a poor prognostic predictor, lacking correlation with gangrene and perforation. Undue reliance on the white cell count may lead to delays in definitive treatment and a higher perforation rate.

CRP measurement is of no diagnostic value in excluding the diagnosis of appendicitis. It would, however, appear that raised white cell count and CRP add weight to an already highly likely diagnosis of appendicitis, and some data suggest that appendicitis is unlikely if both investigations are normal.

3.3    Imaging

Plain abdominal radiography rarely provides helpful information in the work-up of clinical appendicitis and is not currently indicated, having a low sensitivity and specificity, as well as being frequently misleading. If an X-ray has been inadvertently obtained, the presence of a faecolith in the right lower quadrant may favor a diagnosis of appendicitis.

The normal appendix is usually not seen on ultrasonography but, if seen, has a diameter of < 6 mm when compressed with the examining probe. Ultrasound signs of acute appendicitis include a non-compressible appendix > 6 mm in diameter (measured outer wall to outer wall) and visualization of an appendicolith. With perforation, a discontinuous wall of the appendix and prominent pericaecal fat are seen.

Graded compression ultrasonography may be particularly useful in the presence of atypical presentations. In one study it had pooled sensitivity and specificity of 88% and 94%, respectively, for the diagnosis of appendicitis in children. It can also potentially identify other pathologies, especially in female patients. Ultrasound is, however, highly operator dependent, relying on skill and experience. Focused bedside ultra-sound for evaluation of the appendix is an evolving option, with one study reporting sensitivity of 67%, specificity of 92% and overall accuracy of 80% for the diagnosis of acute appendicitis.

The precise role of limited helical computed tomography (CT) in the diagnosis of acute appendicitis awaits clarification, but it appears to be primarily of benefit in equivocal cases. CT signs of appendicitis include distension >6 mm, circumferential thickening of the wall, and periappendiceal inflammation and oedema. Contrast enhancement can be achieved by the intravenous, oral or rectal routes.

Improved diagnostic accuracy with intravenous contrast material has been reported. Sensitivity and specificity of 98% have been reported. The cost of CT scanning can be offset against the cost savings accruing from reduced rates of hospital admission and of negative laparotomy. Compared to ultrasonography, CT has been reported to have superior accuracy for appendicitis in all reported studies. This must be weighed against radiation exposure, availability and the diagnoses under consideration when selecting the preferred test for an individual patient.

A role has more recently been shown for magnetic resonance imaging (MRI) scanning in the diagnosis of acute appendicitis in the pregnant woman, with one study of 51 patients reporting sensitivity of 100% and specificity of 93.6%. The main MRI sign of acute appendicitis is an enlarged fluid-filled appendix >7 mm in diameter.

4.    Treatment

Analgesia, usually small doses of intravenous opioids titrated to the patient’s response, should be given as required, even before the diagnosis is confirmed. There is no evidence that the provision of adequate analgesia is associated with delayed diagnosis, as positive abdominal signs related to peritoneal irritation are not eliminated. Intravenous hydration should also be initiated.

The definitive treatment for appendicitis remains appendicectomy, which may be open or laparoscopic. Laparoscopy is being increasingly preferred, as it allows for combined diagnosis and treatment, as well as the recognition and potential treatment of alternative diagnostic conditions. There is an increase in operative time, but a reduction in postoperative analgesia requirements and length of inpatient stay, as well as earlier return to work. Broad-spectrum antimicrobial agents, when given preoperatively or intraoperatively, reduce the incidence of postoperative wound infection and intra-abdominal abscess.

Conservative management (intravenous hydration and broad-spectrum antimicrobial therapy) may be preferred in the presence of an appendix mass (a surgical decision), or in difficult circumstances when surgical help is not readily available, such as remote locations or while at sea.

Although a negative laparotomy rate of around 15–20% has been accepted in the past, it must be remembered that a negative laparotomy is associated with a more prolonged stay, higher complication rate and measurable mortality. Reducing this remains a major surgical challenge.

Acute Appendicitis in Pregnancy

Acute appendicitis is the commonest non-obstetric reason for laparotomy in the pregnant woman, occurring in about 1 in 1000 pregnancies. Symptoms of appendicitis are similar to those in the non-pregnant state, but in late pregnancy the site of tenderness tends to be higher and more lateral. The incidence of perforation is higher. Fetal loss as a result of appendicitis and laparotomy may be as high as 20%.

Likely Developments over the Next 5–10 Years

• Improved clinical decision support tools.
• Portable bedside ultrasound as part of the emergency department repertoire.
• A focus on a diagnostic strategy that rules out appendicitis while simultaneously ruling in other potential diagnoses.
• Reduction in the negative laparotomy rate to 5% or less.