1. Preliminary imaging

a. Review prior imaging to (a) visualize the abnormality, (b) decide on the appropriate guidance method to be used, and (c) select route for drainage.

b. Immediately prior to the procedure, confirm that the collection is clearly seen with the imaging-guidance method selected and verify safe route to the collection.

c. Preliminary CT

(1) Place the patient in the optimal position for drainage (supine, prone, lateral decubitus) and attach a radiopaque grid over the area of collection.

(a) The lateral decubitus position may help reduce the risk of pleural transgression because it splints the ipsilateral hemithorax.

(b) If possible, both of the patient’s arms are placed above the head to optimize image quality for drainage of upper quadrant collections.

(2) The 5- to 10-mm thick contiguous slices are obtained through the region of interest. If there is concern, bowel (oral, rectal) and/or intravenous (IV) contrast medium may be given and imaging repeated to distinguish collection from surrounding normal structures.

(3) From these preliminary images and with the aid of grid markings, a safe route for drainage is identified and the site of skin puncture, angle of needle entry, and distance to the collection are determined. Occasionally, when there is no safe route for puncture, angling the gantry or changing patient position may reveal a safe path for drainage.

2. Determination of catheter route

a. The optimal path for catheter drainage should consider the size and shape of the abscess and the safest route from skin to collection that does not
transgress vital structures. If possible, an extraperitoneal approach is preferable because this reduces the risk of peritoneal contamination.

(1) When performing fine-needle aspiration alone, it is safe to traverse certain viscera such as liver, kidney, stomach, and small bowel. However, these structures should be avoided as much as possible when using catheter drainage.

(2) Traversing colon and normal pancreas should be avoided because this may risk superinfection of collections or pancreatitis, respectively.

(3) Interloop abscesses in inflammatory bowel disease may not be drainable due to surrounding small bowel loops, although fine needle aspiration may be performed.

b. The usual anterior approach may not be possible in the pelvis due to overlying structures. In such cases, alternative routes such as the transgluteal, transvaginal, or transrectal approaches may be considered.

c. Organ displacement techniques may help displace nonvascular vital structures or create a window for percutaneous needle aspiration or drainage.

3. Diagnostic needle aspiration

a. Prior to drainage, preliminary fine needle aspiration (22-to 20-gauge) of the collection is helpful to determine the nature of the collection. No more than 5 mL of fluid should be aspirated to prevent the cavity from collapsing should catheter drainage become necessary. If fluid is not obtained on initial aspiration and needle tip is optimally placed, then aspiration using a larger needle (18-gauge) may be attempted, with subsequent needles placed parallel and in tandem to the first needle. If no fluid is obtained on reaspiration, then, depending on the clinical suspicion, either a biopsy of the area or a trial with catheter drainage may be performed.

b. When fluid is aspirated, it can be inspected macroscopically, assessing for color, viscosity, turbidity, and smell. Fluid may be sent for laboratory testing to determine its origin. If the question of infection is important, as in the case of a sterile hematoma where catheter insertion may not be desirable, a rapid Gram stain analysis of the aspirate will determine the presence of bacteria and neutrophils. Thus, information from the preliminary needle aspiration can determine if no further action is to be taken, complete needle aspiration alone is sufficient, or catheter drainage is required.

c. If after aspiration the needle is found to be in a good position, it can be left in place and used as a parallel guide to place a catheter into the collection when using the trocar technique (i.e., tandem trocar technique), or it can be used for introduction of an 0.018-in. guidewire as the first step in drainage using the Seldinger technique.

4. Seldinger versus trocar technique

a. Percutaneous catheters are placed using the modified Seldinger or trocar techniques. The particular technique used is determined by the size of the collection, its location, operator preference/experience, and imaging guidance employed.

(1) Generally, large superficial collections are drained using the trocar technique because it is a one-stick procedure that is quick, simple, and safe to perform.

(2) The Seldinger technique is preferred in potentially difficult drainages where the collection is small, is remotely situated, or has limited access.

With this technique, multiple passes can be made using a thin needle such as a 20-gauge Chiba needle or a Ring needle. Once safe access is obtained, the tract can be serially dilated using coaxial exchanges of guidewires and dilators until insertion of a large catheter is possible. However, in inexperienced hands, particularly when not using real-time guidance, several complications including guidewire kinking, loss of access, and catheter malposition can occur.

b. The catheters used commonly range in size from 7 to 14 Fr. and can be either single-lumen or double-lumen (sump).

(1) Larger catheters are traditionally used in the bigger and more complex collections. The 12 to 14 Fr. double-lumen sump catheters should theoretically allow better drainage; however, smaller bore catheters may be just as effective.