Over the past 15 years, improvements in biopsy needle design, sampling technique, and expertise of radiologists and cytopathologists have developed in concert with imaging technologies to make percutaneous needle biopsy (PNB) the most common interventional radiologic procedure. With skills refined from performing PNB, radiologists can now use a new and promising outgrowth of this technique--percutaneous tumor ablation--to safely and accurately place needles into a variety of malignant lesions to deliver local treatment.
Indications for PNB include establishing a diagnosis of a mass at initial presentation; sampling lesions remote from a suspected or known primary malignancy for staging purposes (Figure 1); repeating biopsy of a known tumor following treatment (such as residual tissue after treatment of lymphoma); or determining scar versus tumor at a surgical resection site. Biopsy also may be indicated when an infectious process is suspected, both to rule out malignancy and to direct antimicrobial therapy once an organism has been isolated.1
Traditionally, needle biopsy of focal masses has been used in the chest for suspicious pulmonary nodules, and in the liver. If a lesion can be visualized and a safe path determined, virtually any lesion can be biopsied regardless of its size or location. Parenchymal disease in the absence of a focal mass may also warrant percutaneous biopsy; microscopic evaluation of 18-gauge core tissue samples from the liver or kidney2 usually establishes a diagnosis, thereby allowing appropriate treatment to be instituted.
The choice of an imaging modality to guide needle biopsy depends on the reliability with which the lesion can be demonstrated, the ability of the patient to cooperate (i.e. breath-holding during CT biopsy), the availability of equipment, and personal skill and preference of the radiologist. Sonographic guidance is particularly attractive because of its real-time imaging capability. With ultrasound, delays that may be encountered during the stages of needle placement with CT guidance are avoided, patient motion is less problematic, and angulation in the caudal-cranial direction is facilitated. This is particularly advantageous for small lesions high in the dome of the liver (Figure 2) or in the adrenal.3
Occasionally, lesions may be best visualized with MRI. A variety of nonferromagnetic biopsy devices have been developed to allow MRI localization for biopsy. If these are not available, localization of the lesion with a 22- or 25-gauge conventional biopsy needle can be accomplished with acceptable artifact using MRI. The biopsy can then be performed using tandem placement of additional needles without direct imaging guidance.
Large series indicate that the sensitivity of PNB in the setting of malignancy ranges from 80% to over 90%.4-6 The sensitivity and specificity of PNB vary depending on the nature and location of the lesion biopsied, the skill of the radiologist, and the experience of the pathologist.
When a specific diagnosis is not made by PNB, close follow-up is required, especially in the lung. Samples characterized as "no malignancy identified" can be associated with a malignancy in a third or more of cases because of sampling error.6,7 Therefore, a repeat biopsy should be performed or, if clinical suspicion is high, the lesion should be excised surgically.
Staging and Cytopathology
When possible, biopsy should be performed with the intent to stage a malignancy. That is, obtaining a diagnosis of carcinoma from biopsy of a focal liver lesion in a patient with a pancreatic mass (Figure 3), or an enlarged mediastinal lymph node in a patient with suspected lung cancer, will both diagnose and stage the tumor.
If feasible, the presence of a cytopathologist in the biopsy suite is helpful. Examination of an initial aspirate can dictate whether more material is needed, whether samples are required from elsewhere in the lesion (because of necrosis, for example), or whether additional core samples or bacteriologic studies should be obtained.
The role of aspiration versus non-aspiration sampling techniques is controversial.8,9 The former relies on application of 10 to 20 cc of negative suction to a syringe attached to the needle, while the latter relies on capillary flow to draw cells into the bore of a fine needle. Proponents of the non-aspiration technique cite less contamination of the sample with blood; therefore, we tend to use this technique when initial aspirates have been bloody, particularly in the thyroid. Non-aspiration biopsy is typically less successful in fibrous, very firm tumors such as pancreatic adenocarcinomas.8
The surge of interest in percutaneous biopsy during the late 1970s and 1980s occurred not only because of more widespread use of CT and ultrasound, but also because of the introduction of the fine needle. Fine needles are defined as those with a caliber of 20 gauge or smaller. These needles permit diagnoses to be made inexpensively and with a low complication rate in situations that previously required surgery. The risk of a major complication, such as hemorrhage, from fine-needle biopsy is less than one in 300. The risk of death is less than one in 2000.10-14
These complications can be minimized by assessing patients for a coagulopathy prior to biopsy by using a combination of history and blood coagulation profile. In the absence of a coagulopathy, careful technique results in a wide margin of safety for biopsy, even in a highly vascular organ such as the spleen.13,15
There is an increased risk of hemorrhage with biopsy of hepatocellular carcinomas and hemangiomas of the liver.11,14,16,17 It is advisable to use noninvasive methods to diagnose these conditions when possible. A significantly elevated serum alpha-fetoprotein level can be diagnostic of hepatocellular carcinoma in the appropriate clinical circumstance. Additional imaging studies such as MRI or nuclear medicine tagged-RBC scanning can be helpful in diagnosis of a cavernous hemangioma without the risk of a biopsy. Because of the variable presentations of these reasonably common liver lesions, it is advisable to traverse a band of normal liver parenchyma en route to a lesion to allow tamponade following removal of the needle.17
Other reported complications of PNB include pancreatitis, particularly when normal pancreas has presented as a pseudolesion or is inadvertently biopsied; bile leak; abscess formation; release of vasoactive substances during biopsy of neuroendocrine tumors; and needle tract seeding.18,19,22 Although microscopic evidence of needle tract seeding is not rare, reports of clinically apparent tumor spread are exceedingly uncommon following fine-needle biopsy14 and occur almost exclusively with disseminated malignancy.
Needle biopsy of intrapulmonary lesions carries an additional risk of pneumothorax with varied frequency ranging from 15% to 60%.6,20 A pneumothorax may require treatment if it is large or associated with symptoms. Radiologists who perform lung biopsies must be prepared to insert a small chest-drainage catheter in this situation. A chest tube is required after 5% to 15% of lung biopsies.6,21 When a significant pneumothorax occurs in the early stages of a biopsy and a sample has not yet been obtained, it is recommended that a chest tube be inserted to reinflate the lung and allow the biopsy to be completed successfully at that time (Figure 4).
There is a substantially lower complication rate in biopsies performed with needles ranging from 20 to 25-gauge versus larger needles of 14 to 19-gauge.4 The diagnostic potential of a larger specimen, however, has led to renewed interest in routine biopsy of abdominal, chest, and superficial lesions with 18- and even 16-gauge needles.
Automated core biopsy devices that consist of a "gun" with a disposable needle or disposable spring-loaded biopsy device are typically used. There is no clear evidence that use of 18-gauge core biopsy devices is associated with a higher complication rate than use of fine needles.16,24 Conversely, it has not been established that routine use of these large needles justifies their increased cost. Larger core biopsy needles can be indispensable in centers without an experienced cytopathologist, when histologic architecture is required, for biopsy of benign lesions, and when a large sample volume is necessary. Initial biopsy of lymphoma, low-grade neoplasms, benign tumors of the liver and lung, and possible metastases from breast cancer for estrogen receptors all may benefit from submission of tissue cores.
Several studies have suggested that maximal diagnostic yield results from examination of both fine-needle and core specimens.23,24 If multiple passes are contraindicated, the use of a touch preparation yields limited cytologic and histologic specimens from a single tissue core.25 Evaluation for parenchymal liver disease and renal disease requires the use of 16- or 18-gauge core biopsy devices.
PNB can be performed safely as an outpatient procedure. Local anesthesia often suffices, although particularly anxious or restless patients may benefit from administration of intravenous, short-acting sedatives and/or narcotics. Patients undergoing lung biopsy are given oxygen by nasal prongs. Patients are routinely monitored for two hours following biopsy and if stable, they are discharged in the care of a responsible adult. A card listing the department telephone number and a pager number for the interventional radiologist on call is given to the patient, as are post-biopsy instructions when appropriate. It is important to maintain a biopsy log to identify patients who may require repeat biopsy in the event of a nondiagnostic final result.
Tumor ablation is being investigated in various forms. Heating, cooling, and chemical methods have been used to achieve tissue destruction, both in laboratory and clinical trials. No clear-cut method has been developed as a universal panacea; rather, a tailored approach to individual tumors appears to be developing. Hence, cryotherapy appears effective for prostate carcinoma,26-28 alcohol injection therapy for hepatocellular carcinoma,29-31 and radio-frequency ablation for hepatic metastases.32
Each method has advantages and disadvantages. For example, radio-frequency and laser ablation can be done through fibers that are placed through fine needles. These techniques, however, are limited by the size of tumor they can treat, due to, among other factors, charring effects from heating. Cryotherapy creates rapid and wide tissue destruction, but requires larger tracts than fine needles for probe entry. Alcohol is the cheapest method, but can backleak along the needle tract and the margins of tissue destruction are difficult to control.
These methods are similar to needle biopsy techniques in many respects. First, they are all image-guided--predominantly by ultrasound--as are many percutaneous biopsies. Second, a percutaneous biopsy is obtained from the tissue that is to be ablated in virtually all cases. Third, needle guidance is used to gain access into the lesion to initiate these forms of therapy.
While treatment of selected tumors appears to have promising results, long-term follow-up has not yet been ascertained. Hence, the procedures are still considered investigational for the most part.
Biopsy is now well established and clearly provides cost reduction, compared with typically more invasive surgical procedures. On occasion, another "minimally invasive" procedure may serve as an alternative to biopsy to establish a diagnosis; this might include bronchoscopy for lung biopsy or endoscopy for a biliary biopsy.
Other diagnostic imaging standards with which biopsy must be compared include modalities such as MRI, radionuclide scanning, and PET. When a simple and cheaper serologic test can be obtained and is diagnostic, this should be preferred over biopsy; a prototypical example would be alpha-fetoprotein for hepatocellular carcinoma. Both direct and indirect costs for biopsy and its alternatives will likely weigh more heavily in choosing the appropriate test in the managed-care era.
Dr. Goodacre is an assistant professor of radiology, Dr. Wittich is a professor of radiology and director of interventional radiology, and Dr. Vansonnenberg is chairman of radiology at the University of Texas Medical Branch in Galveston.
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