Complications of diverticulitis affect one in five people with the condition. Those most at risk are aged under 50.

Some complications associated with diverticulitis are discussed below.

Bleeding

Around 15% of people with diverticular disease or diverticulitis experience bleeding, which is usually painless, quick and resolves itself in 70-80% of cases.

However, if the bleeding does not resolve itself, an emergency blood transfusion may be required due to excessive bleeding. If the bleeding is severe, you may need to be admitted to hospital for monitoring.

Urinary problems

Diverticulitis can lead to the inflamed part of the bowel being in contact with the bladder. This may cause urinary problems, such as:

• pain when urinating (dysuria)
• needing to urinate more often than usual
• in rare cases, air in the urine

Abscess

The most common complication of diverticulitis is an abscess outside the large intestine (colon). An abscess is a pus-filled cavity or lump in the tissue. Abscesses are usually treated with a technique known as percutaneous abscess drainage (PAD).

A radiologist (a specialist in the use of imaging equipment, such as computerised tomography (CT) scans) uses an ultrasound or CT scanner to locate the site of the abscess.

A fine needle connected to a small tube is passed through the skin of your abdomen (stomach) and into the abscess. The tube is then used to drain the pus from the abscess. A PAD is performed under a local anaesthetic.

Depending on the size of the abscess, the procedure may need repeating several times before all the pus has been drained. If the abscess is very small – usually less than 4cm (1.5in) – it may be possible to treat it using antibiotics.

Read more about treating abscesses.

Fistula

A fistula is another common complication of diverticulitis. Fistulas are abnormal tunnels that connect two parts of the body together, such as your intestine and your abdominal wall or bladder.

If infected tissues come into contact with each other, they can stick together. After the tissues have healed, a fistula may form. Fistulas can be potentially serious as they can allow bacteria in your large intestine to travel to other parts of your body, triggering infections, such as an infection of the bladder (cystitis).

Fistulas are usually treated with surgery to remove the section of the colon that contains the fistula.

Peritonitis

In rare cases, an infected diverticulum (pouch in your colon) can split, spreading the infection into the lining of your abdomen (perforation). An infection of the lining of the abdomen is known as peritonitis.

Peritonitis can be life-threatening, and requires immediate treatment with antibiotics. Surgery may also be required to drain any pus that has built up, and it may be necessary to perform a colostomy.

Read more about treating peritonitis.

Intestinal obstruction

If the infection has badly scarred your large intestine, it may become partially or totally blocked. A totally blocked large intestine is a medical emergency because the tissue of your large intestine will start to decay and eventually split, leading to peritonitis.

A partially blocked large intestine is not as urgent, but treatment is still needed. If left untreated, it will affect your ability to digest food and cause you considerable pain.

Intestinal blockage from diverticular disease is very rare. Other causes, such as cancer, are more common. This is one of the reasons your GP will investigate your symptoms.

In some cases, the blocked part can be removed during surgery.

However, if the scarring and blockage is more extensive, a temporary or permanent colostomy may be needed.