CHAPTER 22 Percutaneous Biopsy and Drainage
Before the 1980s, open surgery was considered to be the best option for sampling an indeterminate mass or evacuating an infected or symptomatic fluid collection within the abdomen or pelvis. Since then, the development and refinement of percutaneous image-guided techniques have allowed for far less invasive means of accomplishing these objectives. With the proper selection of potential candidates, guidance modality, and approach, image-guided percutaneous techniques have proved safe, efficient, and effective. This chapter discusses some of the considerations and decisions involving percutaneous biopsy and fluid drainage procedures.
The successful performance of a percutaneous intervention involves several steps beyond the physical act of placing a catheter or needle in a patient: (1) Determine necessity and risk; (2) choose target and approach; (3) choose a modality; and (4) assess efficacy.
Most image-guided interventions begin with an initial referral from a clinician who does not routinely perform percutaneous procedures. Therefore, one cannot expect the referring physician to be familiar with all of the details regarding the indications, contraindications, techniques, expected outcomes, and complications associated with the requested procedure. Regardless of the opinion or expertise of the referring physician, the radiologist has a responsibility to assess each potential case independently to determine whether the procedure can be performed safely, whether percutaneous access is the preferred approach, and whether the patient is likely to benefit from the procedure (Fig. 22-1). Rare is the referring physician who will stand by your side in court, taking responsibility for the poor outcome of a nonindicated procedure that you performed at their request. In addition, thorough knowledge of the case at hand projects a sense of competence and confidence to the patient, who will appreciate that you took the time to familiarize yourself with their situation. One should only consider percutaneous biopsy of a mass or organ when patient management or treatment decisions depend on definitive characterization of an abnormality that cannot reasonably be characterized noninvasively. Generally accepted indications for percutaneous fluid drainage include suspected infection, need for fluid characterization, or relief of symptoms. Abscess drainage in the setting of cholecystitis, perforated appendicitis, diverticulitis, or Crohn disease may be indicated as a temporizing rather than curative measure.
Figure 22-1 Enhanced axial computed tomographic image through the midabdomen of a patient with back pain and mildly increased white blood cell count (A) and repeat examination (B) performed within 24 hours of initial study. The referring surgeon insisted on percutaneous drainage of possible right psoas abscess after initial study (A). The radiologist refused, citing concern for ruptured aortic aneurysm. The repeat study (B) confirmed the radiologist’s suspicions, and the patient underwent immediate surgery.
Before performing any biopsy or drainage, one should review all available relevant imaging studies to choose an appropriate target (mass or fluid collection), determine the safest approach to the lesion, and anticipate complications. The most appropriate target for biopsy may not be the lesion initially selected by the referring clinician (Fig. 22-2). Some referring clinicians review diagnostic imaging examinations without ever consulting a radiologist or an official interpretation. Such individuals may refer a patient for biopsy of a particular lesion, unaware that a far more favorable target exists elsewhere in the body. By carefully studying the imaging data in advance, the radiologist can also plan the safest and most direct access to the lesion in question, potentially saving time and consternation during the procedure. Once the access site is chosen, one can estimate the likelihood of certain complications, such as pneumothorax, and appropriately inform the patient.
Figure 22-2 Axial fused data set from positron emission tomographic/computed tomographic study through the pelvis (A) and lower abdomen (B) of a patient with a complex pelvic mass. The referring gynecologist requested biopsy of the hypermetabolic pelvic sidewall component in A. This was noted to surround the iliac vessels by the radiologist, who recommended biopsy of the easier-to-access hypermetabolic right common iliac artery lymph node in B. Biopsy of the lymph node recommended by radiologist yielded the diagnosis of adenocarcinoma.
The choice of an appropriate guidance modality (computed tomography [CT], sonography, fluoroscopy, magnetic resonance imaging [MRI]) is important to the success of any percutaneous intervention. When choosing a modality, one must consider such factors as lesion visibility and location, proximity and visibility of surrounding structures, modality availability, and operator experience.
In the case of percutaneous biopsy, assessing efficacy refers to evaluating the adequacy of the tissue obtained. Unless the radiologist is skilled at reviewing cytology preparations under a microscope, this can best be accomplished by having a cytologist or cytotechnologist review the specimen(s) at the time of tissue sampling. In the case of percutaneous abscess drainage, efficacy can be assessed by imaging the area of interest after catheter placement or fluid aspiration. When a large residual collection persists despite attempts at complete aspiration, repositioning or “upsizing” the needle or catheter may be necessary. In addition to assessing appropriate catheter position and function, repeat imaging allows early detection of procedure-related complications.
Fluoroscopy is rarely used to primarily access a soft-tissue mass or fluid collection within the abdomen or pelvis. However, fluoroscopy may be useful for guiding musculoskeletal procedures based on bony landmarks and may occasionally be utilized to access a superficial air-containing collection requiring drainage. Fluoroscopy greatly facilitates drainage tube manipulations and procedures that require catheter exchanges over a guidewire. Contrast material injected under fluoroscopy can be used to check drainage tube patency and residual abscess cavity size, as well as to delineate fistulous tracts and demonstrate communications between fluid collections. Fluoroscopy may also be a useful adjunct to sonography.
Ultrasound is a popular guidance modality for percutaneous biopsy and abscess drainage (Figs. 22-3 and 22-4). The high temporal resolution of ultrasound facilitates both accuracy and efficiency without subjecting the patient and operator to ionizing radiation. Ultrasound also allows for an unlimited number of imaging planes from which the operator can select the safest projected path. Color Doppler imaging is effective at demonstrating intervening vascular structures, and system portability permits procedures to be performed at the patient’s bedside. Ultrasound is also easy to combine with fluoroscopy. One unique feature of ultrasound is the ability to use it to displace structures such as bowel that lie along the projected needle path. This is accomplished by applying gentle but firm continuous pressure with the transducer over the biopsy site until bowel is displaced to the side. This technique has the added benefit of decreasing the distance from the skin to the target, improving accuracy and target visibility. Unfortunately, the many benefits of sonography are counterbalanced by limited tissue penetration, limited field of view, and the need for an adequate sonographic window. Depending on the background echogenicity, standard needles and catheters may occasionally be difficult to visualize with ultrasound (Fig. 22-5). Visualization of deep structures may be limited in obese patients and in patients with air-filled bowel overlying the region of interest. Air within an abscess cavity may also obscure visualization (Fig. 22-6). The use of tools such as needle guides and echogenic needles designed specifically for ultrasound-guided procedures may improve operator confidence (see Fig. 22-3). If using an adjustable-angle needle guide, one must be certain that the adjustment on the guide matches the angle setting on the ultrasound machine.
Figure 22-4 Pigtail drainage catheter successfully positioned in pelvic abscess using ultrasound guidance. Catheter visibility is excellent due to superficial location and hypoechoic nature of collection.
Figure 22-5 Abdominal abscess drained under ultrasound guidance. Note that drainage catheter is difficult to see because of the echogenic nature of the fluid and deeper location of the collection. Fr, French.
CT provides excellent spatial resolution, field of view, and depth of penetration. However, vascular structures may be difficult to differentiate from surrounding soft tissues on noncontrast CT images, and conventional CT guidance offers relatively poor temporal resolution. Intermittent imaging can be cumbersome for the operator attempting to access a mobile target, and one must rely on estimated trajectories when attempting to avoid nearby structures (Fig. 22-7). Conventional CT imaging is limited to the axial or oblique axial plane (with gantry angulation), lacks portability, and exposes the patient to ionizing radiation.
Figure 22-7 Axial positron emission tomographic (PET)/computed tomographic (CT) image (A) shows hypermetabolic liver metastasis in the right lobe of the liver. Biopsy attempt was unsuccessful under CT guidance because of respiratory motion and poor visibility but was quickly accomplished under ultrasound guidance (B).
The lack of real-time imaging capability has been perceived as a profound weakness of conventional CT guidance. CT-fluoroscopy units, which became available in the 1990s, improved on conventional CT techniques by providing operator-controlled near–real-time imaging capability. Table and scanner controls, as well as image display, are available in the scanner room to allow efficient operation. Therefore, the operator is exposed to ionizing radiation during CT-fluoroscopy procedures and requires shielding such as a lead apron. Radiation exposure to the operator results from scatter, as well as direct irradiation when the operator’s hands are directly within the beam during needle manipulations. Needle holders have been specifically designed to minimize this latter problem, although traditional surgical instruments may also serve to alleviate exposure of the operator’s hands. In most situations, intermittent monitoring with hands outside the radiation beam is sufficient for needle guidance. Improved efficiency still results from close proximity of the operator to the patient and rapid image acquisition and reconstruction. Because of the potential of CT-fluoroscopy to result in unacceptably high radiation doses to patients and operators, care must be taken to reduce patient exposure (e.g., through modification of tube current and exposure times) and operator exposure (e.g., through appropriate shielding and efficient technique). In addition to improving procedure efficiency, CT fluoroscopy has the potential to improve needle positioning and diagnostic yield of difficult percutaneous biopsies (mobile or small targets), and facilitate safe placement of needles around obstacles such as ribs, bowel, and blood vessels (Figs. 22-8 and 22-9).
MRI offers excellent spatial and contrast resolution in addition to a multiplanar capability that has the potential to greatly expand the number of access routes. MRI can take advantage of the intrinsic tissue properties of a lesion to improve conspicuity without requiring intravenous contrast injection. This latter benefit has particular implications for the monitoring of percutaneous ablation therapies. Despite these advantages, the expense and limited availability of MR scanners, as well as the need for MR-compatible equipment and appropriately trained individuals, have limited widespread performance of MRI-guided interventions.
When planning a percutaneous biopsy or abscess drainage, one must choose among the various potential paths by which the lesion can be accessed. When planning access, one should resist the urge to “wing it” when the patient is on the table and should consider the following questions in advance:
When planning access to an abnormality, many options can be considered. These can be organized into anterior or posterior, transperitoneal or extraperitoneal, percutaneous or endoluminal, and transvisceral or nontransvisceral approaches. When considering a transvisceral approach, one should make every attempt to avoid transgressing the pancreas, spleen, gallbladder, colon, uterus, ovaries, and prostate gland, unless the target lesion lies within one of those organs. Some of the more common approaches are discussed in more detail in the following subsections. When planning the approach to a tumor or fluid collection, be sure to look for small but important structures that should be avoided (e.g., the ureters).
The anterior transperitoneal (transabdominal) approach (Fig. 22-11) allows for comfortable supine positioning of the patient. Peritoneal mesenteries and ligaments (e.g., gastrocolic ligament) are transgressed without difficulty. In thin patients, retroperitoneal structures can be approached in this manner. Bowel creates the greatest impediment to this approach. An effort should be made to avoid the inferior epigastric vessels that run deep to the rectus muscles. Avoiding the rectus muscles by puncturing through an aponeurosis may prevent rectus sheath hematoma. Traversing the peritoneum can be painful for the patient, so care must be taken to provide adequate anesthesia.
Patients may be positioned supine or lateral decubitus for the anterior extraperitoneal approach (Fig. 22-12), which is useful for biopsy of pelvic lymph nodes and pelvic sidewall lesions, as well as drainage of iliopsoas abscesses. The ureters, external iliac vessels, and deep circumflex iliac arteries are the main structures to avoid with this approach.
The posterior extraperitoneal (retroperitoneal) approach (Fig. 22-13) usually requires prone or decubitus positioning of the patient but has the advantage of avoiding the intraperitoneal organs. The anterior pararenal approach allows access to many pancreatic fluid collections. A catheter placed in this manner can serve as a guide for a subsequent retroperitoneal surgical approach to the pancreas.
Deep pelvic structures can be approached through the sciatic foramen (Fig. 22-14). Patients are positioned prone or lateral decubitus for this approach. The gluteal vessels and sciatic nerve/sacral plexus are avoided by staying close to the sacrum and below the level of the piriformis muscle. The main limitations of this approach are patient discomfort and limited patient access to the skin entry site for self-care.
Figure 22-14 Enhanced axial computed tomographic image of a deep pelvic abscess (A) inaccessible from an anterior approach. The abscess was successfully drained from a transgluteal approach (B). Access was facilitated by lateral decubitus positioning of the patient.
The liver can be safely traversed when necessary to access fluid collections or biopsy targets within the right adrenal gland, kidney, mesentery, and pancreatic region (Fig. 22-15). An attempt should be made to avoid major hepatic vessels, the gallbladder, and major bile ducts. When placing a transhepatic catheter into an extrahepatic collection, one should try to ensure that no catheter side holes remain within the hepatic parenchyma.