Abdominal Abses: Workup

Workup

Laboratory Studies

• Hematologic parameters suggesting infection (eg, leukocytosis, anemia, abnormal platelet counts, abnormal liver function) frequently are present, although patients who are debilitated and/or elderly often fail to mount reactive leukocytosis or fever.
• Blood cultures indicating persistent polymicrobial bacteremias strongly implicate the presence of an intra-abdominal abscess. Because more than 90% of intra-abdominal abscesses contain anaerobic organisms, particularly B fragilis, postoperative Bacteroides species bacteremia suggests intra-abdominal sepsis.

Imaging Studies

• Plain abdominal radiographs, though rarely diagnostic, frequently indicate the need for further investigation.
  • Abnormalities on plain abdominal films may include a localized ileus, extraluminal gas, air-fluid levels, mottled soft tissue masses, absence of psoas outlines, or displacement of viscera.
  • In subphrenic or even subhepatic abscesses, the chest radiograph may show pleural effusion, elevated hemidiaphragm, basilar infiltrates, or atelectasis.
• In experienced hands, ultrasonography has an accuracy rate greater than 90% for diagnosing intra-abdominal abscesses.
  • Ultrasonography is readily available, portable, and inexpensive. The findings can be quite specific when correlated with the clinical picture.
  • A drawback is that marked obesity, bowel gas, intervening viscera, surgical dressings, open wounds, and stomas can create problems with definition.
  • In addition, the quality of the procedure is operator-dependent.
  • These disadvantages may limit efficacy in postoperative patients.
• CT scan has greater than 95% accuracy and is the best diagnostic imaging method.
  • The presence of ileus, dressings, drains, or stomas does not interfere with reliability.
  • For good anatomical resolution, use oral and intravenous contrast. Oral contrast may help to differentiate a fluid-filled extraluminal structure and a normal intestine. Extravasation of oral contrast indicates a fistula or an anastomotic leak. Intravenous contrast may enhance the abscess by concentrating the contrast material within the abscess wall. The use of oral and intravenous contrast may be limited by the ileus, allergy to contrast material, and renal insufficiency.
  • Identify any occult abscesses using serial images obtained from the diaphragm to the pelvis.
  • The appearance of an air bubble within a fluid collection or a low-attenuation extraluminal mass is diagnostic of an intra-abdominal collection.
  • CT scans can document inflammatory edema in the adjacent fat (obliteration of fat plane) and hyperemia in the abscess wall (enhancement).
  • Drawbacks include nonportability, relative difficulty in diagnosing intraloop abscesses, and, possibly, poor patient cooperation.
  • Recent intra-abdominal surgery also may pose a diagnostic problem in patients in whom intra-abdominal abscesses are suspected. CT scan is not recommended for use in the diagnosis of such abscesses until approximately the eighth postoperative day. By that time, postoperative tissue edema is reduced, and nonsuppurative fluids (eg, hematoma, seroma, intraoperative irrigation fluid) should be reabsorbed. In most postoperative patients, signs of intra-abdominal abscesses do not develop within the first 4-5 days.
• Radioactive agents, such as leukocytes labeled or tagged with gallium-67 or indium-111, may localize the area of inflammation.
  • Such scans are time consuming, and they have many false-positive errors as a result of nonpyogenic inflammatory conditions, bowel accumulation of tagged leucocytes, surgical drains, and incisions.
  • Disadvantages limit such techniques for use in patients in whom intra-abdominal abscesses are strongly suspected, but in whom ultrasound or CT imaging failed to provide adequate diagnostic information.
  • These scans typically do not provide pertinent information that is not found with the CT scan.