Appendicitis

Published on 11/04/2015 by admin

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Appendicitis

Introduction

Acute appendicitis is the most common cause of intra-abdominal infection in developed countries and appendicectomy the most common emergency operation. In the UK, 1.9 females per 1000 have the operation each year compared with 1.5 males, and about 1 in 7 people eventually undergo the operation. Surprisingly, the incidence of appendicitis fell by about 30% between the 1960s and the 1980s, for reasons unknown.

Appendicitis can occur at any age but is most common below 40 years, especially between 10 and 20. It is rare below the age of 10 and very rare below 2 years. Appendicitis is rare in rural parts of developing countries, but the incidence approaches that of the West in the cities. Different susceptibility in similar people is probably related to reduced dietary fibre in city-dwellers.

Acute appendicitis should be considered in any patients presenting to hospital with acute abdominal pain. Even previous appendicectomy does not absolutely rule out the diagnosis. Despite lay impressions, a positive diagnosis is often difficult to make; this is partly because of the lack of specific tests to confirm or exclude appendicitis. At open operation a non-inflamed appendix is sometimes found but a small number of ‘negative’ operations may be unavoidable. Laparoscopy improves diagnostic accuracy, particularly in young women, and is used therapeutically to remove an inflamed appendix; it also has lower complication rates.

Anatomy of the appendix

The appendix is a blind-ending tube arising from the caecum at the meeting point of the three taeniae coli, just distal to the ileo-caecal junction. The appendix base thus lies in the right iliac fossa, close to McBurney’s point. This is two-thirds of the way along a line from umbilicus to anterior superior iliac spine (see below, Fig. 26.6, p. 348). In most cases, the appendix is mobile within the peritoneal cavity, suspended by its mesentery (meso-appendix), with the appendicular artery in its free edge. This is effectively an end-artery, with anastomotic connections only proximally.

The appendix is described as lying in several ‘classic’ sites, but apart from the true retrocaecal appendix, the organ probably floats in a broad arc about its base (see Fig. 26.1). Only inflammation will fix it in a particular place. Its position then determines the clinical presentation. In about 30% of appendicectomies, it lies over the pelvic brim the (‘pelvic appendix’). In some cases, the appendix lies retroperitoneally behind the caecum and often plastered to it by fibrous bands. Thus, an inflamed retrocaecal appendix may irritate the right ureter and psoas muscle, and may even lie high enough to simulate gall bladder pain.

Histologically, the appendix has the same basic structure as the colon. It is covered by serosa (visceral layer of peritoneum) becoming continuous with the meso-appendix serosa. A retroperitoneal appendix has no serosal covering. A prominent feature of the appendix is its collections of lymphoid tissue in the lamina propria. This often has germinal centres and is prominent in childhood but diminishes with increasing age.

The mucosa contains a large number of cells of the gastrointestinal endocrine amine precursor uptake and decarboxylation (APUD) system. These secrete mainly serotonin and were formerly known as argentaffin cells. Carcinoid tumours commonly occur in the appendix and arise from these cells.

Pathophysiology of appendicitis

Appendicitis is probably initiated by luminal obstruction caused by impacted faeces or a faecolith. This explanation fits the epidemiological observation that appendicitis is more common with a low dietary fibre intake.

In the early stages of appendicitis, the mucosa becomes inflamed first. Inflammation eventually extends through the submucosa to involve the muscular and serosal (peritoneal) layers. A fibrinopurulent exudate on the serosal surface extends to any adjacent peritoneal surface, e.g. bowel or abdominal wall, causing localised peritonitis.

By this stage the necrotic glandular mucosa sloughs into the lumen, which becomes distended with pus. Finally, the end-arteries supplying the appendix thrombose and the infarcted appendix becomes necrotic or gangrenous at the distal end and the appendix begins to disintegrate. Perforation soon follows and faecally contaminated contents spread into the peritoneum. If the spilled contents are enveloped by omentum or adherent small bowel, a localised abscess results; otherwise spreading peritonitis develops. Acute appendicitis is illustrated histologically in Figure 26.2.

Clinical features of appendicitis

The pathophysiological evolution of appendicitis and corresponding symptoms and signs are illustrated in Figure 26.3.

Other presentations of acute appendicitis

If the inflamed appendix lies in the pelvis near the rectum, it may cause local irritation and diarrhoea. If it lies near the bladder or ureter, inflammation may cause urinary frequency, dysuria and (microscopic) pyuria, i.e. leucocytes in the urine. These findings may be mistakenly interpreted as urinary tract infection. An inflamed retrocaecal appendix produces none of the usual localising symptoms or signs, but may irritate the psoas muscle, causing involuntary right hip flexion and pain on extension. A high retrocaecal appendix may cause pain and tenderness below the right costal margin. An inflamed appendix near the Fallopian tube causes pelvic pain suggestive of an acute gynaecological disorder such as salpingitis or torsion of an ovarian cyst.

The early phase of poorly localised pain typically lasts for a few hours until peritoneal inflammation produces localising signs. If untreated, the inflamed appendix may become gangrenous after 12–24 hours and perforate, causing peritonitis unless sealed off by omentum. The whole abdomen becomes rigid and tender and there is marked systemic toxicity. Perforation is common in young children. Sometimes, the pathological sequence is extremely rapid and the patient presents with sudden peritonitis.

In older patients, a gangrenous or perforated appendix is more likely to be contained by greater omentum or loops of small bowel. This results in a palpable appendix mass. This may contain free pus and is then known as an appendiceal abscess. As with any significant abscess, there is a tachycardia and swinging pyrexia. An appendix mass usually resolves spontaneously over 2–6 weeks. In the elderly, an appendix abscess is often walled off by loops of small bowel. There may be no palpable mass and the symptoms and signs may not suggest appendicitis. These include non-specific abdominal pain and features of small bowel obstruction due to localised paralytic ileus. Occasionally, appendicitis may present in a most unusual way. Examples include discharge of an appendix abscess into the Fallopian tube presenting as a purulent vaginal discharge, or appendicitis within an inguinal hernia presenting as a groin abscess.

Making the diagnosis of appendicitis

Acute appendicitis is a clinical diagnosis, relying almost entirely on history and examination. Investigations are only useful in excluding differential diagnoses. Ideally, the diagnosis should be made and the appendix removed before it becomes gangrenous and perforates. This markedly reduces the risk of infective complications. However, unnecessary appendicectomies must be kept to a minimum.

Diagnosis of acute appendicitis poses little difficulty if the patient exhibits the classic symptoms and signs summarised in Box 26.1. However, the patient may present at a very early stage, or the signs may have some other pathological cause. At least two out of three children admitted to hospital with suspected appendicitis do not have the condition.

Box 26.1   Cardinal features of acute appendicitis

If evidence for acute appendicitis is insufficient and no other diagnosis can be made, the patient should be kept under observation, admitted to hospital if necessary and re-examined periodically. Eventually, the symptoms settle or the diagnosis becomes clear. Diagnostic laparoscopy may be needed in equivocal cases.

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