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Abdominal Abscesses

by Parswa Ansari, MD

An abscess is a pocket of pus, usually caused by a bacterial infection.

  • Most people have constant abdominal pain and a fever.

  • Computed tomography or another imaging test can distinguish an abscess from other problems.

  • Treatment involves draining pus from the abscess and taking antibiotics.

Abdominal abscesses may form below the diaphragm, in the middle of the abdomen, in the pelvis, or behind the abdominal cavity. Abscesses also may form in or around any abdominal organ, such as the kidneys, spleen, pancreas, or liver, or in the prostate gland.

Causes and Symptoms

Sometimes, abdominal abscesses are caused by perforation of the intestine (see Perforation of the Digestive Tract) due to cancer or injury. More common causes involve spread of infection or inflammation caused by conditions such as appendicitis, diverticulitis, Crohn disease, pancreatitis, or pelvic inflammatory disease. Sometimes abscesses form after injury to the abdomen or after surgery on the abdomen. Specific symptoms depend on the location of the abscess, but most people have constant discomfort or pain, feel generally sick (malaise), and often have a fever. Other symptoms include loss of appetite and weight loss.

An abscess below the diaphragm may form when infected fluid, for example, from a ruptured appendix, is moved upward by the pressure of abdominal organs and by the suction created when the diaphragm moves during breathing. Symptoms may include a cough, painful breathing, and pain in one shoulder—an example of referred pain that occurs because the shoulder and the diaphragm share the same nerves, and the brain incorrectly interprets the source of the pain (see Figure: What Is Referred Pain?).

Abscesses in the mid-abdomen may result from a ruptured appendix, a ruptured intestine, inflammatory bowel disease, diverticular disease, or an abdominal wound. The abdomen is usually painful in the area of the abscess.

Pelvic abscesses can result from the same disorders that cause abscesses in the mid-abdomen or from gynecologic infections. Symptoms may include abdominal pain, diarrhea caused by intestinal irritation, and an urgent or frequent need to urinate caused by bladder irritation.

Abscesses behind the abdominal cavity (called retroperitoneal abscesses) lie behind the peritoneum, the membrane that lines the abdominal cavity and organs. The causes, which are similar to those of abscesses in the abdomen, include inflammation and infection of the appendix (appendicitis) and of the pancreas (pancreatitis). Pain, usually in the lower back, worsens when the person moves the leg at the hip.

Abscesses inside the pancreas typically form after an attack of acute pancreatitis. Symptoms such as fever, abdominal pain, nausea, and vomiting often begin a week or more after a person recovers from pancreatitis.

Liver abscesses may be caused by bacteria or by amebas (single-celled parasites). Bacteria can reach the liver from an infected gallbladder; a penetrating or blunt wound; an infection in the abdomen (such as a nearby abscess), or an infection carried by the bloodstream from elsewhere in the body. Amebas from an intestinal infection reach the liver through the blood vessels. Symptoms of liver abscesses include loss of appetite, nausea, and a fever. A person may or may not have abdominal pain.

Abscesses in the spleen are caused by an infection traveling through the bloodstream to the spleen, by an injury to the spleen, or by the spread of an infection from a nearby abscess, such as one below the diaphragm. Pain may occur in the left side of the abdomen, the back, or the left shoulder.

Diagnosis

Doctors can easily misdiagnose an abscess, because the first symptoms it causes are usually vague and mild and may be mistaken for less serious problems that are more common. If doctors suspect a person has an abscess, they usually perform computed tomography (CT) or sometimes ultrasound scanning or magnetic resonance imaging (MRI). These tests can help distinguish an abscess from other problems (for example, appendicitis), as well as determine the source, size, and position of an abscess. To make a definitive diagnosis, doctors sometimes insert a needle through the skin to draw a sample of pus from the abscess (needle aspiration). The sample is then examined in a laboratory to identify the infecting organism so that the most effective antibiotic can be selected. To guide the placement of the needle, a doctor uses CT or ultrasound scanning.

Treatment

To treat an abdominal abscess, the pus must be drained, either by surgery or by needle aspiration. To guide the placement of the needle, a doctor uses CT or ultrasound scanning. Antibiotics are usually used in conjunction with drainage to prevent the infection from spreading and to help completely eliminate the infection. Laboratory analysis of the pus identifies the infecting organism so that the most effective antibiotic can be selected. It is uncommon for antibiotics to cure an abscess without drainage. If the abscess cannot be reached safely for needle aspiration, surgical drainage may be necessary. Once the abscess has been drained, the source of the infection is also surgically treated. That is, doctors remove the part of the colon that caused the abscess.

Maintaining proper nutrition is important. People may receive nutrition through a tube (enteral) or a vein (parenteral).