The aim of the radiologist is to identify the source of infection or any symptomatic fluid collection, to triage the patients, and to perform image-guided aspiration or catheter drainage procedures to establish diagnosis, relive the symptom, or provide treatment in a safe and timely manner.

CT scan is commonly the first-line imaging modality for establishing the diagnosis. Concomitant use of intravenous contrast and oral contrast increase diagnostic ability and accuracy. When there is suspicion of bowel leakage, administration of water-soluble contrast is mandatory. CT provides excellent axial anatomic information of the patient. However, need for intravenous contrast use and radiation exposure is the main limiting factors. US is easy to perform, with no radiation exposure and no need for contrast use, and provides high diagnostic yield when performed by experienced radiologists. In addition to operator dependency, air in the bowel loops, deeply situated lesions, and large-body habitus of the patient limits use of US as first-line diagnostic or therapeutic modality.

Needle aspiration can be performed to determine the nature of the fluid collection or alleviate symptoms in a noninfected collection such as a pleural effusion or ascites. A catheter drainage procedure is performed in patients with fluid collections that are infected or causing pressure symptoms with the use of 8 to 14 French (Fr) catheters [1]. Percutaneous catheter drainage can be a curative or temporary measure, with a subsequent surgical treatment depending on the nature and extent of underlying disease [2]. Inflammation with concomitant infection of the organ (appendicitis, diverticulitis, and cholecystitis) or any fluid accumulation with or without infection can be an indication for drainage. No clear size criteria exist for the abscess to be drained. Usually, abscesses larger than 3 to 4 cm in their greatest diameter or an infected fluid collection that does not respond to initial antibiotic treatment can be an indication for a percutaneous drainage procedure. Indication, as well as requests for an image-guided drainage procedure for both diagnostic and therapeutic purposes, is increasing because of technical progress and improved success of procedures [3, 4]. The most common indications for catheter drainage are outlined in Table 21-1.

Absolute contraindications are coagulopathy unresponsive to therapy and absence of a safe access route. An uncooperative patient is problematic, but can be treated under general anesthesia or deep sedation. Transgression of major vessels should always be avoided. Transgression of spleen, pancreas, bowel loops, and pleural space should be avoided. Transenteric (jejunum, ileum) routes are considered a contraindication to catheter drainage, but have become a relative contraindication for needle aspiration procedures. Splenic biopsy and percutaneous drainage of splenic abscess can be performed cautiously, especially when the coagulation profile is normal [5]. Liver, kidney, and stomach may be transgressed during needle aspiration or catheter drainage when there is no direct route available. Transrectal, transvaginal, and transgluteal approaches have become regarded as safe routes for deep pelvic fluid collec-tion [6, 7 and 8].

The overall complications rate is 5% to 10%. Mortality ranges from 1% to 6% and is usually a consequence of sepsis or multiorgan failure. The benefits of the drainage in 70% to 90% of cases rest in avoiding the need of a more invasive surgical intervention [9]. When there is no safe access available, surgery should be considered. Medical observation may also be considered, especially for certain pancreatic pseudocysts, with 30% of them known to resolve spontaneously. Abscesses smaller than 3 cm in their greatest diameter can be treated successfully with antibiotics alone and thus may not require percutaneous drainage [2].

Review of the most recent radiologic imaging is essential for the evaluation of locations, extent, and relationship of fluid to vital structures. Imaging modality is chosen based on the location of the lesion and operator experience. The safest and most minimally invasive route should be selected based on the two-dimensional or three-dimensional CT images, even when US-guided procedure is performed. Recent previous intravenous contrast-enhanced CT scans should always be available throughout the procedure for exact anatomic localization. Check coagulation profiles for their appropriate level before the procedure: Prothrombin time (less than 15 seconds), partial thromboplastin time (less than 35 seconds), platelet count (more than 75,000 per mL), and international normalized ratio (less than 1.5). Laboratory work is required within 2 to 3 days prior to the date of the examination to ensure that the patient’s condition has not changed.

Prior to the procedure, anticoagulants should be stopped. For example, aspirin should be stopped a week before; heparin, 6 hours prior to the procedure; and Coumadin, several days before as directed by the referring physician. Discontinuation of anticoagulant is a difficult decision because the interruption of anticoagulant therapy may increases the risk of thromboembolism. The most common indications for Coumadin therapy are atrial fibrillation, the presence of a mechanical heart valve, and venous thromboembolism [10, 11]. Discontinuation of anticoagulant should be directed by the referring physician and by weighing risks and benefits of the procedure to be done. Oral intake, except some medications, should be stopped 4 to 6 hours before the procedure. Nothing by mouth is important for prevention of possible aspiration/asphyxia from vomitus during the procedure and for limiting air introduction into the gastrointestinal tract, which can limit US examination. Oral contrast can be provided 60 to 90 minutes before the procedure and at the CT scan room before the procedure in order to visualize bowel loops. In most of the cases, prior intravenous and oral contrast-enhanced CT scans are used for planning the approach to the collection. Repeat use of contrast at the time of procedure is not required. Obtain intravenous access for hydration and medication with 20-gauge or larger catheter. Antibiotic coverage in patients with an abscess before the procedure is important to reduce septic complications.