MUSCULOSKELETAL PERCUTANEOUS BIOPSY: Techniques and Tips

Chapter 3 MUSCULOSKELETAL PERCUTANEOUS BIOPSY: Techniques and Tips

Image-guided percutaneous biopsy of bone and soft tissue lesions has become integral to modern medical care and is an essential part of the practice of musculoskeletal radiology. This technique has a number of advantages. For example, imaging guidance increases the likelihood of the biopsy being acquired from the lesion if it is small or from viable regions of the lesion if it is large. Imaging also facilitates avoidance of vessels, nerves, organs, and other sensitive structures. Conscious sedation (or in some cases just local anesthetic) may be used rather than the general anesthesia that is associated with surgery. Therefore, percutaneous biopsy can also reduce risk of complications. Percutaneous biopsy has been shown in numerous studies to be safe and effective. However, biopsy must be performed by a radiologist with knowledge of equipment, use of the imaging modalities and relevant anatomy, approaches and potential complications, and limitations of the procedure. This chapter outlines these issues but cannot substitute for practical experience.

EVALUATION OF THE PRE-BIOPSY IMAGING STUDIES

A number of issues should be raised when a percutaneous biopsy is requested. The next step is strongly influenced by findings on recent imaging examinations on which the lesion was diagnosed. These exams should always be reviewed, without exception. The clinical service requesting a biopsy should provide all relevant imaging exams that were performed, and the institutional radiology information system should be searched for prior studies. The following questions should be considered:

1. Should the lesion be biopsied at all? Since there is a risk of morbidity and even mortality with biopsy and sedation, the onus is on the radiologist to make sure that the biopsy is indicated. The fact that the clinician demands it or wants peace of mind should not enter into the decision-making process. If the lesion is clearly benign, a biopsy may cause more harm, and the radiologist is the one who will be held accountable if a complication results.

Conversely, the radiologist interpreting an exam should keep in mind that a report suggesting the presence of infection or tumor may obligate the surgeon to request biopsy, either surgical or percutaneous. If the lesion is clearly benign or noninfectious on imaging, an ambiguous report may be detrimental to the patient and could leave the radiologist at risk for litigation if a complication arises from the resultant invasive procedure. The two main situations in which this occurs are a bone lesion clearly demonstrating nonaggressive features and degenerative disk disease, which is often related to segmental instability. Ways to be more specific about these diagnoses are reviewed in Chapters 5 and 6.

2. Is the lesion too dangerous to biopsy (Box 3-1)? Of course, danger is in the eye of the beholder. Some radiologists are comfortable acquiring biopsies from lesions that others wouldn’t touch (the body of C2 can be accessed through the oral cavity—would you try it?). For each lesion, the radiologist must weigh the benefits and risks based on the level of suspicion and experience in performing the particular approach required. This should be discussed with the referring clinician and the patient. In some cases, although the percutaneous biopsy approach is technically challenging, open surgery may carry even greater risk. This brings up the next principle.

3. Is there a better lesion to biopsy? The clinician often requests biopsy of the lesion that was found on prior exams, but this is not necessarily the best or safest lesion to sample. In suspected metastases, for example, there may indeed be a lesion at C5, but if a pelvic lesion or a lesion at L4 exists, the risk of complication from biopsy of one of these other lesions is clearly reduced. The clinician is often adamant that a particular lesion be biopsied. This may stem from the inexperience of the clinician, and some education is in order. However, sometimes there is good reason to sample the more challenging lesion. For example, for a spine lesion that is to be irradiated or surgically stabilized, one may need to document beforehand the histology of that particular lesion. Reports of patients receiving radiation therapy for spine infection, or for lesions subsequently proven to be benign, support this. If an alternate site is chosen, care must be taken to document that the “safe” lesion being targeted is the same as the other lesion(s) that generated the clinical concern.

4. Does the patient have a bleeding problem? Is the platelet count adequate to initiate clot formation? Are the prothrombin time (PT) and activated partial thromboplastin time (PTT) adequate? The PT and PTT values are usually expressed as a combined value—the international normalized ratio (INR). It is difficult to provide definite cutoff values for biopsy since tolerance of abnormal values depends on a variety of factors, including whether the lesion appears highly vascular on imaging, whether there are adjacent blood vessels, and whether the lesion is deep or in a noncompressible location. If there is a concern, fresh frozen plasma (FFP) can be infused 1 to 2 hours before the procedure to temporarily normalize the values.

5. Is it infection or tumor? Could it be amyloid? These questions rarely influence the decision to biopsy once the lesion has been identified by the radiologist as being of concern. However, after the sample is acquired, decisions must be made regarding whether to send the sample to microbiology, pathology, or both. In general, it is prudent to also consider infection when tumor is the working diagnosis and to consider tumor when the lesion is suspected to be infection. Of course, if there is articular or disk involvement, tumor is much less likely; this rule of thumb applies mostly to atypical infections such as fungal and mycobacterial infections, which can appear masslike and simulate tumor. If the patient has renal failure and amyloid is suspected, the pathologist needs to be alerted to this because Congo red stain may be needed to test for amyloid.

6. In the case of tumor, could the course of the biopsy needle result in contamination of a potential myocutaneous flap? This is especially important when biopsy of a primary bone or soft tissue tumor is performed. Metastasis and myeloma are mainly treated systemically. In a primary lesion, the approach must always be discussed with the physician who will perform the definitive surgery because he or she will be the one deciding (assuming the worst-case scenario such as sarcoma) what flap to use during resection. Often this necessitates a more complicated and technically difficult biopsy approach. The surgeon may request that the tract be marked with methylene blue as the needle is removed. Also, based on the suspected tumor type, the pathologist may need a larger quantity of tissue (e.g., a larger core) to study the lesion architecture.

7. In the case of infection, could the needle course spread infection to bone, joint, or tendon sheath? In a common clinical scenario, a patient may have cellulitis, and a bone biopsy or joint aspiration is requested. If the needle passes through the infected tissue into uninvolved bone or synovium, these tissues can become infected as well. Therefore, the approach should always avoid overlying infected tissue. Again, this may complicate the procedure and requires more planning. The exception to this is when the bone or joint is clearly infected on imaging and when biopsy/aspiration is being performed to document the infecting organism.

8. Can the patient tolerate the biopsy? The patient should be asked beforehand whether he or she can tolerate the position required for biopsy. Occasionally, a biopsy is planned only to find out that the patient cannot lie on the stomach for more than a few minutes (e.g., because of recent surgery). A moving target makes for a dangerous biopsy, and whether voluntary or involuntary, motion should be minimized. Altering patient position to accommodate comfort can complicate the procedure (e.g., taking a biopsy of the spine with the patient on his/her side). Respiratory problems can not only cause problems with positioning but may also prevent use of conscious sedation. Patients who are uncooperative may need to be sedated more deeply to avoid excess movement.

EQUIPMENT

Guidance Modalities

An essential aspect to keep in mind when planning a biopsy is that the lesion should be visible on the guidance modality. Alternatively, if the lesion is extensive or infiltrative, the lesion itself need not be visible, just the region involved. Fluoroscopy has definite advantages over other modalities. For example, imaging is easily performed in real time. The limitation of projectional radiographic imaging is not a major one considering how easy it is to alter the angle craniocaudally or transversely to acquire a different viewpoint. Biopsies using fluoroscopy are often easier to schedule as well. However, the room and configuration of the fluoroscopy equipment (C-arm, fixed-image intensifier, angiography room) can create problems with access to the biopsy area and must be considered in advance. Many angiography units have a narrow work area, which can cause problems when a long biopsy needle is used. Also, some C-arms and angiography units cannot achieve the angulations needed for the desired approach.

For most lesions, CT is the preferred guidance method. Simultaneous visualization of the lesion and soft tissue structures such as blood vessels is extremely helpful for planning the approach, especially for small or deep lesions. The angle of approach can be planned to avoid vital structures, and assessment of the depth to the lesion assists in needle selection. Repeat scans can be acquired in the plane of the needle when changes in needle position are made. CT fluoroscopy assists in speeding this process: Instead of leaving the suite for each scan, the operator remains in protective lead and steps on a foot pedal to almost instantly acquire a small series of images through the needle. Disadvantages of CT include relatively high radiation dose and limitation regarding craniocaudal angulation.

Ultrasonography is very versatile and can also be used for localization of soft tissue lesions (Fig. 3-1). Obviously, because ultrasound does not visualize within bone, it generally cannot be used for bone biopsy localization except for superficial lesions or those with cortical breakthrough. Ultrasound with Doppler easily visualizes blood vessels and can improve the safety of the desired approach. Solid and vascular regions of soft tissue masses can also be accurately targeted. The needle passage can be directly visualized in real time rather than periodically after repositioning.

Figure 3-1 Ultrasound-guided biopsy.

MRI is used in some centers for localization but requires special preparation (Fig. 3-2). If equipment is needed (e.g., to provide sedation and monitoring) it must be MRI-compatible (e.g., all components must be nonferromagnetic). In addition, needles must be MRI-compatible and made of a material that creates relatively little artifact so that the needle tract is well visualized with reference to surrounding anatomy. MRI can be useful for ablation because the destroyed tissue can be visualized (e.g., ice ball formation in cryoablation).

Figure 3-2 MRI-guided biopsy. MRI-compatible needles are available. Using T1 spin echo or STIR, lesions are visible and artifact is kept to a minimum, facilitating biopsy. This technique is useful for cryoablation as well as biopsy, the latter especially when the lesion is only visualized on MRI.

(Courtesy of John Carrino, MD, MPH, Baltimore. (Carrino JA, Blanco R: Magnetic resonance-guided musculoskeletal interventional radiology. Semin Musculoskelet Radiol 2006;10[2]:159–174.)

Needles

Fine-Needle Aspiration

Fine-needle aspiration needles are used for collection of cytology samples; needles are small gauge and collect groups of cells rather than core samples. The needle is placed within the lesion with stylet in place. The stylet is removed while using an “in-and-out” motion within the lesion; changing direction with each pass while pulling the stylet out collects the sample. Alternatively, a syringe can be attached to the needle hub and aspiration performed while the needle is manipulated. The sample is placed into cytology fluid; in the lab the sample is spun down into a block and evaluated.

Fine-needle aspiration is especially useful because low-profile needles may reduce the risk of damage to adjacent tissues. However, unless real-time imaging is performed during needle manipulation (i.e., ultrasound) the in-and-out motion is performed blindly and may not be advised for lesions near vital structures. Another disadvantage is that the architecture of the lesion is altered and the sample volume is small, making it more difficult to make the diagnosis, especially for primary lesions. Nevertheless, some authors have recommended that a cytology sample be acquired in addition to the core biopsy sent to the histology department for increased diagnostic yield overall.

Diagnostic yield is highly dependent on the experience of the interpreting cytologist or pathologist. Close communication between the radiologist and the pathologist is important to give feedback in both directions. The radiologist should discuss radiologic findings with the pathologist, especially for atypical cases, and the pathologist should provide feedback to the radiologist regarding the quality of the samples acquired that may require a change in needle type or methodology.

Needles have a variety of configurations and tips designed to offer different advantages. Since there are many needles and vendors are continually modifying them, it is difficult to discuss the specific features of each. However, some general features can be outlined with reference to their intended purpose.

Coaxial Systems

Coaxial systems are needles that have an outer sheath and an inner cutting needle and are intended for either soft tissue or bone (Figs. 3-3 and 3-4). The cutting needle extends a certain distance beyond the sheath. This is almost universally used in musculoskeletal biopsies because it requires only one localization/placement procedure to position the sheath/stylet at the margin of the lesion, after which multiple passes can be obtained. The only situation in which a non–coaxial system may be used is a very superficial lesion that is easy to localize and that is not near any vital structures (Figs. 3-5 and 3-6).

Figure 3-3 Coaxial bone biopsy needles. Cook Elson/Ackermann 14 G pictured. Available with solid or hollow stylet. Hollow version is especially useful for accessing difficult lesions; after a 22-G vanSonnenberg needle is passed safely to the site, the entire hub can be removed and the Ackermann needle passed over the needle down to the lesion. Multiple biopsies can be acquired coaxially through the sheath.

(Courtesy of Catherine Roberts, MD, Scottsdale, AZ.)

Figure 3-4 Bone biopsy needles. RADI Bonopty 15 G with eccentric drill. This is a coaxial system that is very advantageous for penetrating thick cortex.

(Courtesy of Catherine Roberts, MD, Scottsdale, AZ.)

Figure 3-5 Noncoaxial bone biopsy needles. MD Tech 11 G with TrapLok pictured. This is not a coaxial system, therefore it is disadvantageous for most image-guided biopsies. After advancing the biopsy needle into bone, inserting the TrapLok device is intended to hold the sample in place.

(Courtesy of Catherine Roberts, MD, Scottsdale, AZ.)

Figure 3-6 Noncoaxial bone biopsy needles. Bard Ostycut 15 G pictured. This system has been limited by lack of a coaxial design. However, the short version is useful for biopsy of superficial bones.

(Courtesy of Catherine Roberts, MD, Scottsdale, AZ.)

Soft Tissue Guns

Soft tissue guns collect a core of tissue unlike with fine aspiration needles (Fig. 3-7). They are larger gauge—typically 14 to 18 G. Rather than having a hollow cutting needle design, they incorporate a solid inner core with a recess near the tip. This portion of the needle is advanced into the lesion, after which an inner sheath “shoots” over it, cutting the tissue filling the recess. The system is then withdrawn from the outer sheath and the sample is collected. Therefore, two components are advanced in succession: the solid inner needle and the inner sheath. In some needles this is automated, triggered by a button that is pressed when the needle is in position. However, it is not always desirable to shoot the inner needle without feel or control. For example, if the lesion is near a vital structure or not as large as the “throw” of the needle, it is better to retain control of the first step. Some needles have a setting or alternate triggering mechanism that allows the radiologist to slowly advance the inner needle as far as desired; when in position, the sheath is triggered to advance.