Intra-Abdominal Abscesses

Intra-abdominal abscesses are classified as intraperitoneal, retroperitoneal, or visceral (see table Intra-Abdominal Abscesses).

Many intra-abdominal abscesses develop after perforation of a hollow viscus or colonic cancer. Others develop by extension of infection or inflammation resulting from conditions such as appendicitis, diverticulitis, Crohn disease, pancreatitis, pelvic inflammatory disease, or indeed any condition causing generalized peritonitis.

Abdominal surgery, particularly that involving the digestive or biliary tract, is a significant risk factor: The peritoneum may be contaminated during or after surgery by events such as anastomotic leaks. Traumatic abdominal injuries—particularly lacerations and hematomas of the liver, pancreas, spleen, and intestines—may develop abscesses, whether treated operatively or not.

The infecting organisms typically reflect normal bowel flora and are a complex mixture of anaerobic and aerobic bacteria. Most frequent isolates are

• Aerobic gram-negative bacilli (eg, Escherichia coli and Klebsiella)

• Aerobic gram-positive cocci (eg, Enterococcus fecalis)

• Anaerobes (especially Bacteroides fragilis)

Abscesses may form within 1 week of perforation or significant peritonitis, whereas postoperative abscesses may not occur until 2 to 3 weeks after operation and, rarely, not for several months. Although manifestations vary, most abscesses cause fever and abdominal discomfort ranging from minimal to severe (usually near the abscess). Paralytic ileus, either generalized or localized, may develop. Nausea, anorexia, and weight loss are common.

Abscesses in the Douglas cul-de-sac, adjacent to the rectosigmoid junction, may cause diarrhea. Contiguity to the bladder may result in urinary urgency and frequency and, if caused by diverticulitis, may create a colovesical fistula.

Subphrenic abscesses may cause chest symptoms such as nonproductive cough, chest pain, dyspnea, hiccups, and shoulder pain. Rales, rhonchi, or a friction rub may be audible. Dullness to percussion and decreased breath sounds are typical when basilar atelectasis, pneumonia, or pleural effusion occurs.

Generally, there is tenderness over the location of the abscess. Large abscesses may be palpable as a mass.

• Abdominal CT

• Rarely radionuclide scanning

CT of the abdomen and pelvis with oral contrast is the preferred diagnostic modality for suspected abscess.

Other imaging studies, if done, may reveal abnormalities. Plain abdominal radiographs may reveal extraintestinal gas in the abscess, displacement of adjacent organs, a soft-tissue density representing the abscess, or loss of the psoas muscle shadow. If there are abscesses near the diaphragm, chest radiographs may reveal abnormalities such as ipsilateral pleural effusion, elevated or immobile hemidiaphragm, lower lobe infiltrates, and atelectasis.

A complete blood count and blood cultures should be done. Leukocytosis occurs in most patients, and anemia is common.

Pelvic Abscess (CT Scan)

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This CT scan shows an abscess (red arrow) in the pelvis caused by appendicitis. Note the radio-opaque fecalith (white arrow).

Image provided by Parswa Ansari, MD.

Occasionally, radionuclide scanning with indium-111–labeled leukocytes may be helpful in identifying intra-abdominal abscesses, but this modality has been largely replaced by high-quality CT.

• IV antibiotics

• Drainage: Percutaneous or surgical

Almost all intra-abdominal abscesses require drainage, either by percutaneous catheters or surgery (1, 2). Exceptions to drainage include small (< 2 cm) pericolic or periappendiceal abscesses, or abscesses that are draining spontaneously to the skin or into the bowel. Drainage through catheters (placed with CT or ultrasound guidance) may be appropriate given the following conditions:

• Few abscess cavities are present.

• The drainage route does not traverse bowel or uncontaminated organs, pleura, or peritoneum.

• The source of contamination is controlled.

• The pus is thin enough to pass through the catheter.

Antibiotics are not curative but may limit hematogenous spread and should be given before and after intervention. Therapy requires IV antibiotics active against bowel flora and sometimes other antimicrobials.

Patients with community-acquired infection should be characterized as at low or high risk of treatment failure or death based on signs of sepsis or septic shockmetronidazole

Patients previously given antibiotics or those who have hospital-acquired infections should receive antibiotics active against resistant aerobic gram-negative bacilli (eg, Pseudomonas) and anaerobes. (See also the Surgical Infection Society's 2017 revised guidelines on the management of intra-abdominal infection.)

Nutritional support is important, with the enteral route preferred. Parenteral nutrition should begin early if the enteral route is not feasible.

Outcome for a patient with complicated intra-abdominal abscesses (those extending beyond a single organ into the peritoneal space) depends mainly on the presence of sepsis and on the patient’s primary illness or injury and general medical condition rather than on the specific nature and location of the abscess.