Abdominal trouble

Peritonitis can be hard to pin down, with varying causes and signs, but can also be serious. Karen Coumbe MRCVS explains its diagnosis and treatment

- Karen Coumbe

PERITONITIS means inflammation of the peritoneum, which is the protective thin membrane layer within the abdomen. It is nature's biological “wrapper”, lining the abdominal cavity and acting as a protective covering over the abdominal contents.

The inside of the abdomen is called the peritoneal cavity, which is a large space in a horse. The peritoneum not only acts as a protective wrapping but also secretes serous fluid (at a rate of about 60ml per hour in a horse) to lubricate and cleanse the abdomen with its antibacterial properties. This produces a healthy environment for the gut, so that the various structures glide smoothly and do not stick together.

When the normal smooth peritoneal surfaces become inflamed, the area becomes sore and irritated, and this is peritonitis. In people if you have a ruptured appendix, you will develop peritonitis. In horses, colic and peritonitis are closely linked - one condition may lead to the other and both must be taken seriously.

WHY DOES IT HAPPEN?

PERITONITIS is often thought to be caused by abdominal infection, and sometimes bacteria are involved. There are however many possible underlying causes, such as trauma: for example, a stake wound that penetrates the abdomen or a foaling or breeding accident leading to perforation of the uterus.

More commonly the cause is an area of diseased gut where the natural defences are impaired and the gut becomes “leaky”, allowing bacteria to reach the peritoneum.

It is also possible for horses to develop peritonitis because of a tumour or possibly an internal abscess such as after a severe strangles infection, the so-called “bastard strangles”. Yet another possibility is parasite migration, for example worm damage.

Vets may be unable to establish the underlying cause for a case of peritonitis - sometimes you know what is wrong, just not why.