Chapter Outline
Choice of Modality for Image Guidance
Specific Organ-Related Techniques
The acquisition of tissue from lesions that are neither visually apparent nor palpable has evolved from being performed in the operating room by surgeons to being performed percutaneously by radiologists with image guidance. Image-guided percutaneous biopsies have also evolved from being reserved for large and superficial lesions to include small, deep, and precariously positioned lesions. With these changes has come a trend toward more outpatient procedures, fewer complications, and lower cost. Because radiologists are willing to perform biopsy of more challenging lesions, there has also been a trend toward imaging techniques with real-time guidance, such as ultrasonography (US) or computed tomography (CT) fluoroscopy. In the past, the success of image-guided biopsies has depended not only on the expertise of the radiologist but also on that of the cytopathologist. Whereas a proficient cytopathologist is extremely advantageous, often enabling a sample consisting of only a minimal amount of tissue to be diagnostic, the increased use of core or cutting biopsy needles has diminished the overall impact of that contribution.
The role of image-guided percutaneous biopsy is mainly to diagnose or to exclude the presence of malignant disease, to stage patients with a known malignant neoplasm, to monitor the response to tumor therapy, to confirm or to exclude recurrent tumor, and to differentiate whether nodal enlargement is due to tumor or infection. Furthermore, biopsy techniques can be used to diagnose nonmalignant medical diseases in the liver and kidneys. For these “medical”-type biopsies, larger bore needles are generally required to obtain specimens for histology.
The challenge facing radiologists is to provide a biopsy service whereby adequate tissue can be readily obtained from almost any lesion in the abdomen and pelvis, on almost any patient, with near real-time needle-tip visualization during both placement and sampling. This has numerous implications related to the coagulation status and condition of the patient, the choice of imaging modality, the choice of type and gauge of needles, and the transgression of normal structures. This chapter discusses the details of these techniques in a systematic fashion including the preprocedural evaluation, choice of modality for image guidance, choice of needles, biopsy planning, specific organ-related details, and complications.
Preprocedure Evaluation
A complete preprocedure evaluation is an important component of an efficient and effective biopsy service. This evaluation should consist of reviewing prior diagnostic imaging studies, obtaining a bleeding history and appropriate laboratory studies, and obtaining written informed consent. We have found that incorporating physician extenders into the procedural approval process helps ensure that biopsies are performed as efficiently and safely as possible. Integration of physician assistants, nurse practitioners, and nurse coordinators allows the radiologist to focus on the procedure, improving throughput. Furthermore, many of these patient encounters, whether they are performed on an inpatient or elective outpatient basis, can be coded and billed as a specialty consultation, allowing the radiology group to be reimbursed appropriately.
Review of prior diagnostic imaging studies will confirm the presence of a lesion suitable for biopsy and help in planning of a specific approach, choice of the appropriate guidance modality, and characterization of the lesion to provide the pathologist with an appropriate differential diagnosis. The importance of reviewing prior imaging studies cannot be overstated. For example, a radiologist may be asked to biopsy a lesion that, on review, proves to be a benign hemangioma or cyst.
The appropriate laboratory investigation of the patient before a biopsy remains the subject of debate. No single published guideline is widely accepted or used. This lack of consensus stems from the fact that no prospective evaluation of a large number of patients has been performed in which various factors, including patient history, specific type of procedure, and laboratory tests, have been compared with outcome.
Silverman and colleagues proposed a strategy for screening laboratory tests for abdominal interventional procedures based primarily on the bleeding risk of the procedure and screening of patients for bleeding tendencies. Since the work by Silverman and coworkers, consensus guidelines have been published by the Society of Interventional Radiology ( Table 71-1 ). The recommendations are based on available literature and consensus expert opinion but, admittedly, lack high-level evidence. As a result, the recommendations can conflict with other publications. For example, in a review by O’Connor and associates, the international normalized ratio (INR) and platelet transfusion threshold for percutaneous liver biopsy were 2.0 or lower and 25,000/mL or higher, respectively, whereas, the Society of Interventional Radiology guidelines recommend an INR and platelet transfusion threshold of 1.5 or lower and 50,000/mL or higher, respectively. The lack of high-level data contributes to the nonuniform pattern regarding management of hemostatic defects. It is likely that individual practitioners will tailor their guidelines to local expertise and patient comorbidities.
Category | 1 | 2 | 3 |
---|---|---|---|
Procedure | Low bleeding risk, easily detected and controllable (e.g., paracentesis, superficial aspiration, and biopsy) | Moderate bleeding risk (e.g., intra-abdominal or retroperitoneal biopsy) | Significant bleeding risk, difficult to detect or to control (e.g., renal biopsy) |
Tests | INR: recommended only for patients receiving warfarin or with known or suspected liver disease | INR: recommended | INR: recommended |
aPTT: recommended only for patients receiving unfractionated heparin | aPTT: recommended only for patients receiving unfractionated heparin | aPTT: recommended | |
Platelet count: not routinely recommended | Platelet count: not routinely recommended | Platelet count: recommended | |
Hematocrit: not routinely recommended | Hematocrit: not routinely recommended | Hematocrit: recommended | |
Management | INR: correct to ≤2.0 | INR: correct to ≤1.5 | INR: correct to ≤1.5 |
Platelets: recommend transfusion ≤50,000/µL | Platelets: recommend transfusion ≤50,000/µL | Platelets: recommend transfusion ≤50,000/µL | |
aPTT: no consensus | aPTT: no consensus | aPTT: correct so that value is ≤1.5 times control | |
Hematocrit: no consensus | Hematocrit: no consensus | Hematocrit: no consensus |
A patient’s bleeding risk is also influenced by medication use, with emphasis on anticoagulant and antiplatelet agents. Anticoagulant medications have traditionally included warfarin and unfractionated heparin. Newer anticoagulants include low-molecular-weight heparin (e.g., enoxaparin), indirect factor Xa inhibitors (e.g., fondaparinux, idraparinux, idrabiotaparinux), direct Xa inhibitors (e.g., rivaroxaban and apixaban), and direct thrombin inhibitors (e.g., lepirudin, argatroban, bivalirudin, dabigatran). The lack of objective data evaluating the periprocedural management of patients receiving anticoagulant or antiplatelet agents makes the proposal of general recommendations for the interventionalist difficult. The American College of Chest Physicians has proposed stratifying patients on the basis of risk for perioperative thromboembolism. Patients are classified as being at low, moderate, or high risk for thromboembolic events ( Table 71-2 ). By use of this classification scheme, patients with the highest thromboembolic risk and scheduled to undergo a procedure with a high hemorrhagic risk (e.g., renal biopsy) stand to benefit the most from interruption of anticoagulation and bridging with an anticoagulant with a short half-life (e.g., enoaparin). In observational studies, this regimen was associated with a 1% to 2% incidence of thromboembolic events in the high-risk group. There is a paucity of evidence to guide the use of bridging anticoagulation for moderate- and low-risk categories.
INDICATION FOR ANTICOAGULATION | |||
---|---|---|---|
Risk Stratum | Mechanical Heart Valve | Atrial Fibrillation | VTE |
High (>10% annual risk of thromboembolism) | Any mitral valve prosthesis Any caged-ball or tilting-disk aortic valve prosthesis Recent (within 6 months) stroke or TIA | CHADS 2 score of 5-6 Recent (within 3 months) stroke or TIA Rheumatic valvular heart disease | Recent (within 3 months) VTE Severe thrombophilia (e.g., deficiency of protein C or S or antithrombin, antiphospholipid antibodies) |
Moderate (5%-10% annual risk of thromboembolism) | Bileaflet aortic valve prosthesis and one or more of the following risk factors: atrial fibrillation, prior stroke or TIA, hypertension, diabetes, congestive heart failure, age >75 years | CHADS 2 score of 3-4 | VTE within 3-12 months No severe thrombophilia (e.g., heterozygous factor V Leiden or prothrombin gene mutation) Recurrent VTE Active cancer (treated within 6 months or palliative) |
Low (<5% annual risk of thromboembolism) | Bileaflet aortic valve prosthesis without atrial fibrillation and no other risk factors for stroke | CHADS 2 score of 0-2 (assuming no history of stroke or TIA) | VTE > 12 months previous and no other risk factors |
If anticoagulation can be withheld, it is frequently helpful to allow a time lapse of five half-lives, which corresponds to a residual drug activity of 3% from the initial dose. Whereas making decisions based on the half-life of a drug is reasonable, clearance can be affected by drug-drug interactions, differences in metabolism, and genetic influences. If a procedure requires more urgency, an elevated INR may be reversed immediately by administering fresh frozen plasma. Alternatively, vitamin K can be used to reverse the effects of warfarin. An elevation of partial thromboplastin time induced by heparin may be reversed with protamine, a heparin antagonist. Low-molecular-weight heparin (i.e., enoxaparin) has a half-life of 4.5 to 7 hours, based on anti-Xa activity. In general, most percutaneous interventions in the abdomen and pelvis can be performed after withholding of the therapeutic dose on the morning of the procedure.
Similar to anticoagulants, antiplatelet agents can also increase a patient’s hemorrhagic risk during surgery. Platelet inhibitors include aspirin, thienopyridines (clopidogrel, prasugrel, ticlopidine), and glycoprotein IIb/IIIa inhibitors (e.g., abciximab, eptifibatide, tirofiban). Appropriate management of antiplatelet agents is determined by the indication. Most common indications include secondary prevention of ischemic cardiac events, post–coronary stenting, and secondary prevention of cerebrovascular events. Stopping of these agents should be considered carefully. At our institution, it is common to consult the treating cardiologist before cessation to better understand the risks associated with stopping of the medication against the hemorrhagic risk of the procedure. If a cardiac event occurred within 1 year and the patient is taking aspirin or clopidogrel, we generally perform the biopsy without stopping the medication but inform the patient of the increased hemorrhagic risk. Aspirin, clopidogrel, prasugrel, and ticlopidine irreversibly inhibit platelet function, making the half-life of the drug irrelevant. For each day that one of these agents is withheld, approximately 10% to 14% of the normal platelet function is restored, taking 7 to 10 days for the entire platelet pool to be replenished. On the other hand, dipyridamole, cilostazol, and nonsteroidal anti-inflammatory drugs reversibly inhibit platelet function, and their effects are dependent on the elimination half-life. The Society of Interventional Radiology has published consensus guidelines on appropriate management of anticoagulant and antiplatelet medications ( Table 71-3 ).
Medications | Category 1 Procedure (Low Bleeding Risk) | Category 2 Procedure (Moderate Bleeding Risk) | Category 3 Procedure (Significant Bleeding Risk) |
---|---|---|---|
Warfarin | Withhold 3-5 days (INR ≤ 2.0) | Withhold 5 days (INR ≤ 1.5) | Withhold 5 days (INR ≤ 1.5) |
Heparin (unfractionated) | No consensus | No consensus | Withhold 2-4 hours before procedure |
Low-molecular-weight heparin (therapeutic dose) | Withhold 1 dose or 12 hours before procedure | Withhold 1 dose or 12 hours before procedure | Withhold 2 doses or 24 hours before procedure |
Aspirin * | Do not withhold | Do not withhold | Withhold 5 days before procedure |
Clopidogrel * | Withhold 0-5 days before procedure | Withhold days before procedure | Withhold for 5 days before procedure |
* Patients unable to safely discontinue medications for any number of medical reasons, including but not limited to recent coronary or cerebrovascular stents, should be afforded a degree of variance from these guidelines.
Written informed consent should be obtained from each patient. The biopsy procedure should be described to the patient thoughtfully in layman’s terms. Patients should be informed of the risk of bleeding and infection and that biopsy of upper abdominal lesions may result in a pneumothorax and possibly chest tube placement. Patients should be informed that multiple needle passes may be required, the specimen may not be diagnostic, and additional work-up may be necessary. Patients with lesions near bowel are at risk of bowel injury and abscess, although this complication, surprisingly, has only rarely been reported. The preprocedure visit is also an excellent opportunity to assess various factors, such as the patient’s airway, ability to lie in the desired position, and level of anxiety. All these variables play a role in deciding the level of sedation (i.e., moderate sedation, often administered by the radiologist, or a higher level of sedation requiring an anesthesiologist). A detailed home care instruction form is reviewed with each patient before the biopsy that explains which symptoms are to be expected after the biopsy and which symptoms raise the question of a complication. This form provides a list of contact telephone numbers in case a complication occurs.
Choice of Modality for Image Guidance
Numerous modalities are available for performing image-guided percutaneous biopsies: fluoroscopy, US, CT (with or without fluoroscopic capability), and magnetic resonance imaging (MRI). Each of these techniques has strengths and weaknesses as well as specific indications, and they are discussed next.
Fluoroscopy
Fluoroscopy is used sparingly within the abdomen and pelvis and is reserved for lesions that are large, superficial, or calcified. Fluoroscopy can also be used on occasion to perform a biopsy of obstructing lesions, such as a cholangiocarcinoma located adjacent to or surrounding a surgically or endoscopically placed stent. US, however, can also accomplish this task. Preliminary cross-sectional imaging with CT, US, or MRI is important to determine which intervening structures the needle may transgress en route to the lesion.
Ultrasonography
The use of US for image-guided biopsies is generally preferred for its accuracy, safety, decreased costs, decreased procedure time, widespread availability, multiplanar capabilities, and flexible patient positioning. US has the major advantage of direct real-time visualization of the needle tip during both placement and sampling. This advantage not only aids in avoiding blood vessels but also helps ensure that sampling is restricted to the lesion. Furthermore, compression with the US transducer is a major advantage in that it not only reduces the distance between the skin surface and the lesion but also displaces bowel and other structures. Color Doppler US should be used to assess lesion vascularity and to avoid transgression of nearby vascular structures.
Careful sampling of the lesion alone is particularly important in certain scenarios, such as in differentiating a hepatocellular adenoma from focal nodular hyperplasia. The conspicuous absence of bile duct epithelium in adenomas is the key to differentiating these two hepatocyte-containing lesions. Therefore, if one is performing a biopsy of an adenoma and the needle tip ventures beyond the margins of the lesion into normal hepatic parenchyma, the bile duct constituents that are aspirated may cause the cytopathologist to inadvertently diagnose the lesion as a focal nodular hyperplasia. This could lead to an error in diagnosis, which is important to avoid; many adenomas are surgically resected because they are considered to be premalignant and can undergo spontaneous hemorrhage.
The disadvantages of US include the obscuration of some lesions by intervening lung, bone, or bowel. An angled approach or transducer compression can be used to improve visualization. Needle-tip visualization can be difficult with modern transducers that are narrowly collimated. This difficulty can be reduced by using an attached needle guide. Visualization can also be poor in larger patients, in whom sonographic tissue penetration is poor. Finally, ultrasound of solid abdominal viscera is limited in the setting of tissue heterogeneity (e.g., liver cirrhosis). Contrast-enhanced CT and MRI are excellent tools to detect lesions within solid organs. Image fusion of contrast-enhanced CT or MRI examinations with US allows ultrasound-guided biopsies to be performed with high success ; however, the technique requires additional hardware for needle tracking and software for coregistration.
The two main techniques of US-guided biopsies are the freehand technique and the attached needle guide technique. The freehand technique has the advantages of allowing many more degrees of freedom and the ability to separate the needle and the transducer, an approach that often results in better needle visualization. The main disadvantage is the steep learning curve because needle-tip visualization can be difficult and time-consuming. The attached needle guide has the advantages of a shallow learning curve with easier and quicker needle-tip visualization. Disadvantages include a significant reduction in the degrees of freedom and the modest cost of the apparatus.
Computed Tomography
CT is widely used for image guidance in the United States primarily because of equipment availability and user preference. CT has the advantages of very high spatial resolution and lack of imaging “blind spots.” Furthermore, the depiction of intervening structures is superb. Disadvantages include the exposure to ionizing radiation, the lack of direct real-time needle-tip visualization, the difficulty encountered in the biopsy of moving lesions, and the high cost. Although CT is limited to the axial plane, the ability to angle the gantry up to 30 degrees allows some limited flexibility in needle placement, particularly in the cephalocaudal direction. An alternative to angling the gantry is to use the triangulation method, in which three points composed of the lesion (A), the skin overlying the lesion (B), and a point either cranial or caudal to the lesion (C) are selected in the same parasagittal plane. The position of C should be selected such that a line formed between A and C does not transgress any critical structures (see later, routes to avoid). These three points form a right triangle, and by trigonometry, the length and angle of insertion can be calculated ( Fig. 71-1 ).
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CT fluoroscopy is capable of providing six to eight lower resolution and low-milliampere images and near real-time needle-tip visualization. This technique reduces the time advantages of US considerably and improves the targeting of moving lesions. It is particularly useful for procedures involving deep structures, such as retroperitoneal masses, or for procedures involving organs prone to respiratory motion, such as the liver. CT fluoroscopy may use a quick check technique, which is analogous to conventional CT. This technique uses single-section CT fluoroscopic images to check needle location and to confirm appropriate alignment. Continuous CT fluoroscopic images may be obtained in the region of the needle when the needle tip is difficult to localize, such as when it is in an oblique or a transverse plane. This technique is analogous to conventional CT, except reconstruction times are faster and the radiologist may manually position the table. Continuous fluoroscopy denotes the use of continuous fluoroscopic exposure during needle advancement or manipulation. It is wise to use forceps as a needle holder to prevent primary beam irradiation of the radiologist’s hands.
Radiation doses to the patient and radiologist are higher in CT fluoroscopy than in conventional CT; however, observed doses have fallen with the trend toward the quick check technique and modulation of two scanner parameters, which are usually readily displayed: CT dose index and dose-length product. These parameters can be lowered by modifying the longitudinal scan length, number of scans, and tube current–exposure time product (milliampere × second [mAs]).
Solid masses, which are isodense to surrounding organ parenchyma, are difficult to biopsy. Intravenous contrast material may be administered to increase lesion conspicuity. We recommend administering intravenous contrast material after placement of the guide needle or biopsy needle near the lesion, based on anatomic landmarks.
Magnetic Field–Based Electronic Guidance System
Electromagnetic navigation systems have been developed to aid in near real-time needle tracking. The technology uses real-time positioning information obtained when a probe containing embedded sensors is moved within a magnetic field during CT- or US-guided procedures. The postprocessed images allow the operator to quickly assess the needle trajectory before entering the patient’s skin. As the needle is advanced down to the lesion, the screen displays the real-time needle position by overlaying it on a preprocedural CT or US set of images. This technology helps facilitate out-of-plane biopsy approaches.
Magnetic Resonance Imaging
MRI has been used sparingly for guiding percutaneous biopsies, although the roadblocks to use of this modality are diminishing. The advantages of MRI include high spatial resolution, very high inherent tissue contrast, lack of ionizing radiation, real-time capability, and virtually unlimited multiplanar imaging planes, which facilitates needle placement for lesions not readily accessible with a traditional axial approach ( Fig. 71-2 ). Disadvantages include the requirement for MR-compatible supplies and monitoring equipment, the considerable time commitment, and the high cost. Many of these disadvantages, however, are significantly reduced or eliminated with the open or dedicated interventional units, which allow placement of the needle while the patient is in the bore of the magnet and use fast imaging sequences that provide near real-time guidance. The use of lower field strength in an open system decreases the signal-to-noise ratio and results in longer acquisition times but may still be sufficient for lesion visualization. The high inherent tissue contrast attainable on noncontrast MRI can be a major advantage; in most practices, this modality is used selectively in patients with lesions that are not well seen on US and CT. This imaging scenario, however, is infrequent in the abdomen.
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Choice of Needles
In choosing a needle for image-guided biopsy, the first issue to address is what technique will be used to acquire the sample. A single-needle technique uses a new needle for each pass. This is limited by the necessity of imaging guidance for each pass, resulting in long procedure times, need to traverse structures with each pass, increase in the risk of complications, and increased radiation exposure when CT guidance is used. In the tandem technique, a small-caliber needle is first used to localize the lesion with image guidance. A larger caliber biopsy needle is then advanced parallel to the localizing needle without imaging guidance. This technique is limited by multiple organ punctures and imprecise needle-tip localization. At our institution, most operators use a coaxial technique, during which a guide needle is advanced down to the lesion under imaging guidance. Biopsy needles are then advanced coaxially through the guide needle. The drawbacks include having to use a larger caliber guide needle to accommodate the biopsy needle and that subsequent passes may follow the same path and yield little diagnostic tissue.
Guide needles are available in a wide range of size, length, and tip configuration. In general, the needles used for biopsies in the abdomen and pelvis range in size from 16- to 19-gauge and 5 to 20 cm in length. The tips of the guide needles may have an angled bevel or a stylet with a sharp point. A drawback of the beveled needles is that they may deflect away from the intended target as they pass through tissue interfaces, which renders accurate needle placement somewhat more difficult. Needles with a pointed stylet tend to track along a straight line. The Hawkins-Akins needle (Cook Medical, Inc., Bloomington, Ind) also contains an interchangeable blunt stylet, which reduces the risk of injury to bowel, nerves, and blood vessels.
Many biopsy needles are available. These can be broadly grouped into aspirating and cutting needles ( Fig. 71-3 ). The aspirating needles are usually 20- to 25-gauge and are designed to yield individual cells or small clumps of cells that can be spread into a single cell layer for cytopathologic analysis. The “skinny” 22- or 25-gauge needle, although in widespread use, is very flexible and particularly susceptible to bending and deflection. At times, however, the purposeful bending of such a thin-gauge needle can aid in targeting lesions that would be difficult to access otherwise. A curved needle placed coaxially through a straight needle is advantageous because it can compensate for inaccurate guide needle placement and can also sample different regions of a lesion without having to manipulate the outer needle. If a curved needle is used without a guide needle, care should be taken in inserting the needle as rotation of the needle may result in a lacerating effect.
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Many radiologists attach a syringe and tube to the needle to apply suction during the actual biopsy. We have abandoned the use of this suction method in favor of simply removing the stylet and relying on natural capillary forces and mechanical agitation to draw tissue into the needle. The main advantage of the nonsuction technique is that the specimens are usually free of blood. Fibrin clots form quickly within bloody aspirates, rendering them difficult to smear onto a glass slide. Also, the presence of abundant erythrocytes obscures cellular detail.
The cutting needles, usually 14- to 20-gauge, are designed to obtain a core of tissue suitable for histologic analysis. Most radiologists have adopted the use of automated cutting needles. These automated needles have an inner slotted stylet for the specimen and an outer cutting stylet. They consistently provide an excellent core of tissue. Manufacturers have designed single-use automated or semiautomated cutting needles that are so lightweight they will maintain their position during the movement of patients in and out of the CT gantry. Cutting needles with a short, long, or adjustable excursion are available. Many of these needles lend themselves to a coaxial technique, permitting several biopsy samples to be obtained from a single skin and organ puncture. In a blinded evaluation of 20 automated cutting biopsy devices, the best overall performance was obtained with 18-gauge needles with at least a 2-cm excursion.
It has been suggested that radiologists should use the smallest gauge needle possible in performing biopsy procedures. Researchers have explored the effect of needle gauge on organ bleeding in the pig model. This work shows that in general, larger needles produce greater bleeding. The research also shows that large needles yield greater amounts of tissue. To the extent that each needle pass carries risk, the maximum tissue yield can be obtained at minimum risk by performing fewer passes with a larger needle. There are two caveats to consider. First, cytopathologists prefer to analyze a thin layer of single cells or clumps of cells. Samples obtained from thin needles (i.e., 20- to 25-gauge) may be easier to smear into a single cell layer than samples from larger needles (14- or 18-gauge). Second, use of cutting needles is riskier than use of aspirating needles. If the knifelike blade of the cutting needle encounters an artery or a vein, the vessel will be lacerated and bleed. In contrast, aspirating needles tend to displace rather than to cut tissue.
MRI is used to guide tissue biopsies particularly in the central nervous system and breast. Dedicated MR-specific needles are now available, although the selection of biopsy needles and sizes is considerably more limited than with the ferromagnetic needles traditionally used in US and CT cases. These nonferromagnetic needles are readily visualized as a signal void and are safe to use in the magnetic field. Use of a ferromagnetic needle, on the other hand, can cause considerable image distortion that may obscure the lesion of interest and hinder precise needle localization. In addition, they may be torqued or deflected in the magnetic field, raising questions about their safety.
It is vital to coordinate needle selection with the pathologist who will interpret the case. If the pathologist is skilled in cytopathology, small-bore (20- to 25-gauge) aspirating needles are recommended. If the pathologist prefers samples for histologic analysis, larger bore cutting needles are appropriate. Some groups perform a cytopathologic touch preparation for samples obtained with core needles. This technique allows a rapid preliminary diagnosis and preserves the core material for permanent fixation and sectioning.
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