Clinical Review: Acute appendicitis.(Disease/Disorder overview)

Section 1: Epidemiology and aetiology

Appendicitis is defined as in- flammation of the appendix.

This condition is common, yet notoriously difficult to diagnose. This diagnosis can be associated with a variety of severe consequences and should be regarded as a clinical emergency.

The appendix is a blind-ending luminal structure that arises from the caecum. The average length of the appendix is 8-10cm. Several lymphoid follicles are scattered in its mucosa. These follicles increase in number between eight and 20 years of age.

The intra-abdominal position of the appendix varies from the right upper quadrant to the suprapubic region, which explains the different ways in which the condition presents. The appendix is most classically found in the right iliac fossa (RIF) and is retroperitoneal in two-thirds of patients.

The lifetime incidence of appendicitis is 6 per cent and 70,000 appendectomies are carried out every year in the UK. Men have a slightly higher lifetime risk of appendicitis than women and there is a slightly increased risk associated with western living, possibly due to a low-fibre diet. A small familial predisposition exists. The incidence of appendicitis gradually increases from birth, peaks in the late teens and declines with increasing age.

Aetiology

The pathophysiology of acute appendicitis begins with obstruction of the lumen of the appendix. A particularly common cause of this is a faecalith, lumps of inspissated faeces that can be found in the lumen of the appendix.

Another common cause is lymphoid hyperplasia. This is associated with various disorders including Crohn's disease, gastroenteritis, amoebiasis, measles, mono- nucleosis and many other viral illnesses. For this reason, it is a particularly common cause of appendicitis in childhood.

Another significant cause of appendicitis in the older age groups is neoplastic processes around the base of the appendix, causing obstruction. Less common causes include bacteria (including yersinia and histoplasma), parasites (such as schistosome species and pinworms) and TB.

Congenital disorders of appendix anatomy are extremely rare but are occasionally reported as causing appendicitis.

Whatever the cause of the obstruction to the appendiceal lumen, the result is an increase in luminal pressure due to continued secretion of fluids from the appendix mucosa and the stagnation of faecal material and bacterial overgrowth. This leads to an influx of white blood cells and the formation of pus.

If this …