The aim of the interventional radiologist is to detect and localize symptomatic fluid collections, ascertain if additional imaging or laboratory tests are needed, and determine what, if any, intervention is required. Close communication between interventional and critical care staff is essential to accomplish these goals. Image-guided aspiration or drainage procedures can alleviate symptoms due to mass effect or inflammation, provide fluid samples for laboratory characterization, and cause reduction in sepsis [5]. A list of fluid collections amenable to image-guided procedures is provided in Table 22.1.

CT and ultrasound are the two main imaging modalities used for percutaneous image guidance. Magnetic resonance imaging (MRI)-guided drainage is available at some academic institutions, but limited by availability, cost, and paucity of MRI-compatible devices. The choice between CT and ultrasound is ultimately determined by operator experience, availability of equipment, and nature of the collection such as size, location, and presence of septations. Advantages of ultrasound include portability, lack of radiation, low cost, and real-time visualization of needle placement into a collection. Ultrasound can also be readily combined with fluoroscopic guidance techniques. Limitations of ultrasound include poor visualization of deep collections secondary to large body habitus, bone, overlying bowel gas, or surgical dressings. CT provides excellent visualization of the fluid collection and its relation to vital structures, allowing for the safest percutaneous access route to be chosen. For deep collections such as those located in the pelvis or retroperitoneal space, CT is particularly well suited [6]. There is typically a shorter learning curve to master CT-guided procedures, especially given the availability of commercially produced skin grids to help aid needle placement. The main limitations of CT include radiation exposure, cost, and lack of real-time visualization of needle placement. The recent advent of CT fluoroscopy allowing the operator to obtain rapid sequential images of needle position without having to leave the patient is a major step forward for helping to resolve some of these technical issues [5]. Table 22.2 is a summary of the advantages and limitations of CT versus sonography [7].

The indications for image-guided drainage and aspiration include, but are not limited to, fluid sampling to assess infected versus sterile collections, reduction of microorganism burden due to extraction of contaminated material, and relief of pressure symptoms secondary to excess fluid accumulation. In the critically ill patient, catheter drainage may stabilize the patient’s condition so that a more definitive surgical procedure can be performed at a later time [8,9]. Abscess size is an important determinant of the need for percutaneous drainage. Many patients with abscesses smaller than 4 cm in diameter can be treated conservatively with broad-spectrum antibiotics, hydration, and bowel rest [10]. If a small collection is unresponsive to initial antibiotic therapy, a drainage procedure should be considered. In patients with abscesses larger than 4 cm, studies have shown that percutaneous catheter placement is beneficial and less invasive than surgical intervention [10]

Contraindications are divided into absolute and relative. Absolute contraindications for percutaneous drainage include absence of a safe access route or uncorrectable coagulopathy. An uncooperative or unwilling patient may also cause termination of a procedure. Often, the study may be rescheduled
to allow for general anesthesia or deep sedation to be provided for patient safety. The utmost care should be taken to avoid transgression of major blood vessels, pleura, pancreas, and spleen. One should also avoid prolonged drainage of sterile collections due to the risk of secondary infection [11]. In patients with relative contraindications, procedures may require more planning or additional time, but are usually amenable to treatment. For example, a transenteric (small bowel) route may allow for needle aspiration of a collection previously thought to be inaccessible [12]. If no direct route is available, the liver, kidney, and stomach may be safely transgressed during needle aspiration or catheter placement. Recent advances in technique such as transgluteal, transvaginal, or transrectal sampling provide more options for draining difficult-to-reach collections [13,14,15].

Overall complications associated with percutaneous drainage are reported to be less than 15% [16]. These include damage to vital structures, bleeding, and infection among others. Mortality (ranging from 1% to 6%) is frequently secondary to sepsis or multiorgan failure rather than the drainage procedure itself. Depending on the location and physical properties of an infected or sterile collection, percutaneous drainage is curative in 75% to 90% of cases [6,16,17]. In approximately 10% of cases, percutaneous drainage can serve as a temporizing measure allowing surgery to be postponed or performed in a single step [10]. Patients whose drainage collections contain feculent material or a fistulous communication tend to respond poorly, and further surgical intervention may be required. Indications for surgery also include visceral perforation, peritonitis, uncontrolled sepsis, and lack of improvement or deterioration of clinical status following several days of medical treatment [18].

Regardless of the study to be performed, certain basic principals apply to all patients about to undergo a drainage procedure. After review of the risks, benefits, and alternatives to the procedure, informed consent should be obtained from the patient or health care proxy. The radiologist should review the case with the referring physician to determine if the procedure is medically indicated or if other treatment alternatives exist. A comprehensive history and physical examination is taken, including review of previous and current imaging studies to evaluate fluid collection size, location, and complexity. Determination of the imaging modality used to characterize the fluid collection depends on location and operator preference. Once the collection has been localized, the access route is planned. The basic tenets of surgical drainage are followed using established surgical routes to find the shortest and least invasive path while avoiding lung, pleura, bowel, and other vital structures. Prior to the procedure, the patient should stop all anticoagulant medications, given the benefits of the drainage procedure outweigh the risk to the patient from thrombosis. For example, clopidogrel (Plavix), an antiplatelet agent, should be held for 7 to 10 days before the procedure [19]. For patients receiving vitamin K antagonists such as Coumadin, guidelines recommend bridging anticoagulation with therapeutic dose low-molecular-weight heparin (given subcutaneously) or intravenous unfractionated heparin (given intravenously) [19,20]. The goal is to maintain the international normalized ratio (INR) less than 1.5. It is believed that anticoagulants can be safely restarted 6 to 8 hours following the procedure. Coagulation parameters should also be obtained within a few days before the procedure and corrected if necessary. In a nonemergent situation, the prothrombin time (PT) should be less than 15 seconds, the partial thromboplastin time less than 35 seconds, platelet count greater than 75,000 per mL and INR less than 1.5. In emergent situations where the PT is elevated, fresh-frozen plasma should be given. Platelet transfusions can be administered just prior to the procedure to raise levels to an acceptable value.