appendix

appendix The appendix is more correctly known as the ‘vermiform appendix’, meaning worm-like. It is present only in man, certain anthropoid apes, and the wombat (a nocturnal, burrowing Australian marsupial). Many herbivores are provided with a comparable, but larger structure, in which bacterial breakdown of cellulose, the main constituent of cell walls in plant fibre, takes place. In man the appendix is thought to represent a vestigial organ — one that remains in diminished form after it has ceased, in evolutionary terms, to have any significant function.

The appendix is a short, blind-ended tube arising from the caecum, the first part of the large intestine, within the lower right part of the abdominal cavity. In about half the population, the appendix is ‘retrocaecal’ — behind the caecum; in most cases, it is mobile within the abdominal cavity, suspended from the rest of the bowel by a sling-like fold of tissue (a mesentery), which has the artery to the appendix running in its free edge. The appendix first appears in the fetus at about 6 weeks of development, being initially high up in the abdomen but later descending to its final position. Approximately 1 in 100 000 people are born without an appendix — and very rarely there are two. The appendix is typically 6–9 cm long, but the length varies considerably, from 2 to 30 cm; on average it is 0.5 cm longer in the male than in the female. It is longer in the child than in the adult and shrinks further after mid life. The internal diameter of the appendix is described as wide enough to admit a matchstick, but this lumen may be partially or completely obliterated after middle age. The structure of the tube is basically the same as that of the large intestine: it has an outer muscular coat lined by a much-folded lining (mucosa). It also has aggregates of lymphoid tissue within its walls, which may replace the muscle coat in places.

The appendix in man is medically important because of its propensity to become inflamed in the condition known as acute appendicitis. In this condition, the appendix becomes swollen and the wall fills with inflammatory cells. The process may be initiated by blockage with material from the bowel. If this inflammatory process is allowed to continue, the appendix will become gangrenous and perforate, leading to peritonitis. Acute appendicitis is the most common cause of intra-abdominal infection in developed countries and appendicectomy is the most commonly performed emergency surgical operation. It is less common in developing countries where the diet contains significantly more fibre than our own. In the UK, 1.9 females and 1.5 males per thousand of the population each year get acute appendicitis and have their appendix removed. At the current rate, one in every 6 or 7 people will eventually undergo appendicectomy, even though the incidence of acute appendicitis in the UK has decreased by 50% since the 1970s. The mortality from acute appendicitis has also fallen dramatically, due to a number of factors including better general nutrition, earlier presentation to hospital, and improved anaesthetics. Post- operative problems, such as wound infection, have also become rarer due to the widespread use of antibiotics before surgery. Although appendicitis can occur at any age, it is commonest between 8 and 14 years. It is rare in the elderly and in infants below the age of 2. The cardinal sign of appendicitis is abdominal pain, which is often rather vague and poorly localized initially. As the inflammatory process proceeds, however, the pain usually localizes to the right side of the lower abdomen over the site of the appendix. There is tenderness over the appendix, often accompanied by a slight fever, a facial flush, and a rapid pulse. Despite this apparently typical picture the diagnosis is often difficult to make, particularly in females in whom gynaecological problems are also common and may closely mimic appendicitis. A percentage of appendices removed prove to be normal when examined under the microscope.

The first record of what may have been appendicitis was made by Aretaios around the third century ad. Though the appendix appeared in the anatomical drawings of Leonardo da Vinci from 1492, it was not until 1521 that it was described by an Italian anatomist, Berengario da Carpi. While there is some debate as to who first removed an appendix in England, the first deliberate appendicectomy for acute appendicitis was undertaken by a gynaecologist, Robert Lawson Tait, in May 1880 in Birmingham. The patient recovered. Prior to this Claudius Amyand, physician to Queen Anne, in 1736 successfully removed an acutely inflamed appendix from inside the hernial sac of a young boy.

A. Winter, and P. J. O'Dwyer

Bibliography

Knut, H., (ed.) (1989). The illustrated history of surgery. Harold Starke, London.

See also alimentary system.