Intra-abdominal abscess: causes, symptoms, drainage and recovery

An abscess is a pocket of pus, made up of white blood cells, bacteria and debris, that the body walls off from the surrounding tissue. Inside the abdomen it may sit next to the bowel, in the pelvis, beneath the diaphragm or within an organ such as the liver. The NHS describes it, in the context of appendicitis and diverticulitis, as a build-up of pus (abscess) in or near the bowel.

It is different from a skin abscess, which the NHS describes as a painful lump on the skin containing pus that can sometimes be treated in a GP surgery. An abscess inside the abdomen cannot be seen or felt in the same way, and it is nearly always managed in hospital.

Most intra-abdominal abscesses arise when infection or bowel contents escape from the gut or another organ. The NHS lists the complications of a burst appendix as including peritonitis, sepsis and an abscess, and says that diverticulitis can rarely lead to an abscess, a blockage, a fistula or a hole in the bowel. It lists a burst stomach ulcer, a burst appendix, Crohn's disease or diverticulitis, pancreatitis and surgery among causes of peritonitis, and says that abscesses can develop in the lining.

The NHS appendicitis page also notes that, in rare cases, an abscess can form where the appendix was removed, and advises an urgent GP appointment or NHS 111 if you have recently had an appendectomy and develop concerning symptoms.

Symptoms depend on where the abscess is, but commonly include persistent or worsening tummy pain, a high temperature or feeling hot, cold or shivery, and feeling sick. The NHS lists tummy pain, a very high temperature or feeling hot, cold or shivery, a rapid heartbeat, passing much less urine, loss of appetite, feeling or being sick and a swollen tummy as symptoms of peritonitis, which can accompany or follow an abscess.

For diverticulitis the NHS advises asking for an urgent GP appointment or NHS 111 for tummy pain that is getting worse or does not go away, a high temperature, or being sick and unable to keep fluids down. It advises calling 999 or going to A&E for severe tummy pain with vomiting, a swollen tummy or being unable to poo or fart, or for confusion, pale or blotchy skin, a very high or low temperature or breathlessness, which could be signs of sepsis.

Diagnosis combines examination, blood tests that look for infection and imaging. The NHS lists CT scans and ultrasound among the tests used in suspected appendicitis and diverticulitis, and scans such as CT are how a collection of pus is shown and located. The doctors will also look for the underlying cause, which may involve further tests such as the colonoscopy or flexible sigmoidoscopy the NHS lists for suspected diverticular disease.

NHS Lothian's clinician guidance recommends taking blood cultures before starting antibiotics in complicated abdominal infection and sending samples from any drainage for testing so that antibiotics can be matched to the bacteria.

Treatment usually has two parts: antibiotics and removing or draining the pus. The NHS says peritonitis is treated in hospital, usually with antibiotics through a vein, and that abscesses sometimes need to be drained with a needle under local anaesthetic. For diverticulitis complications it says treatment may be with antibiotics or surgery, for example surgery to drain an abscess or remove an infected part of the bowel, and that some people need a colostomy.

NHS Lothian guidance describes source control, either surgery or radiological drainage, as vital for complicated diverticulitis, and notes that a total antibiotic course is counted from the point of adequate source control and that longer courses may be needed when an abscess cannot be drained. Your team decides between drainage guided by imaging and an operation according to the abscess and how unwell you are.

Recovery depends on the cause and the treatment. If a drain has been placed you will be shown how it is cared for and when it is likely to be removed, and the team will check the output and repeat imaging as needed. Return of fever, increasing pain, redness or leaking around a drain site, or feeling unwell after discharge should be reported straight away. As the NHS notes for sepsis, recovery after a serious infection can take weeks or months, and it suggests being patient, sleeping well, eating a balanced diet and building up exercise gradually.

Abdominal abscesses are emergencies and are dealt with through NHS emergency departments and surgical teams. Private hospitals can also treat them. The important point, in either setting, is that the source of infection is found and dealt with promptly, as the NHS Lothian guidance on source control makes clear.