Image-Guided Percutaneous Biopsy

Needle Choice

Fine-needle biopsies are obtained with 20- to 25-gauge needles ( Table 17-1 and Fig. 17-1 ). There are a wide variety of needle types and needle tip designs on the market. Broadly, fine-gauge needles can be divided into those with a sharp beveled tip (e.g., Chiba or spinal needles for simple aspiration) or those with a modified, tissue cutting tip (see Table 17-1 ). The advantage of using a needle with a cutting tip is that a core of tissue may be obtainable with this needle type. The author’s personal preference is the Turner needle for all fine-needle biopsies. Advantages of fine-needle biopsy include the ability to traverse bowel without ill effect, and the likelihood of inducing hemorrhage when sampling vascular lesions is minimal. In the author’s practice, fine-needle biopsy is performed on virtually all lung biopsies, all neck biopsies, and in abdominal biopsies wherein the patient has a known primary with liver or other lesions that are thought to be metastases ( Box 17-1 ). Large-gauge needle biopsies (14- to 19-gauge) are almost universally performed with a spring-activated, modified Tru-Cut system ( Box 17-2 ). Many such systems of variable gauge, throw length, and design are available ( Fig. 17-2 ). Most are disposable needle systems, although some, such as the Bard biopsy gun, can be used repeatedly with disposable needles. This is the least expensive option, in that, once the biopsy gun is obtained, only the needles need be replaced. The author’s preference is for a nondisposable biopsy gun and disposable 18- and 20-gauge needles. Advantages are (1) ease of use, (2) ability to hold the biopsy gun with one hand, which is particularly important when using ultrasound guidance, and (3) uniform consistency in size and amount of tissue obtained. This is a major advantage over non-automated large-gauge biopsy systems, wherein the consistency of the tissue obtained is directly related to the operator’s skill. Using an automated system, the biopsy procedure is fast and the biopsy needle system does not remain in the patient for long. Anecdotally, patients appear to experience less pain than when conventional large-gauge biopsy systems are used. In general, large-gauge automated needle biopsies are performed in patients in whom there is no known primary tumor, when there is a possibility of lymphoma, or after fine-needle biopsy has failed (see Box 17-2 ).

In recent years, this distinction between large-gauge biopsy and fine-needle biopsy has become blurred because of the development of 20-gauge automated Tru-Cut needles. These 20-gauge needles are considered to be in the fine-needle category but obtain a core of tissue like any other Tru-Cut needle. These needles are now used more and more frequently, particularly when an experienced cytopathologist is not present for the biopsy procedure.

Image Guidance

CT and sonography are the two main image guidance modalities used for biopsy procedures. Although magnetic resonance interventional systems are used in clinical practice, their role in performing routine biopsies is limited by cost and lack of widespread availability. The choice between CT and sonography is largely guided by clinician preference and the nature, size, location, and site of the lesion. All neck and soft tissue lesions, most liver lesions, large abdominal masses, and some pancreatic lesions can be biopsied under sonographic guidance. Mediastinal lesions, most pancreatic, retroperitoneal, adrenal and pelvic lesions, and some liver lesions are biopsied under CT guidance. The relative advantages and disadvantages of CT and sonography are listed in Table 17-2 .

Sonography

Sonography should be used for image guidance because it provides continuous real-time needle visualization. There are many commercially available biopsy guides that can be fitted to existing ultrasound transducers that will direct the needle into the path of the ultrasound beam. The author prefers to use a freehand approach with the needle inserted through the skin into the plane of the ultrasound beam. The freehand technique offers more flexibility in that needle position and angle adjustments can be made as the biopsy is being performed to correct or realign the needle path if necessary.

The transducer can be covered with a sterile sheath using sterile K-Y Jelly as an acoustic coupling agent. Alternatively, the transducer can be sterilized by painting the surface with Betadine. The author’s unit tends to use a sterile cover. The skin is cleansed with Betadine and the lesion located in the center of the ultrasound beam. The shortest and safest path to the lesion is chosen. The needle is aligned with the ultrasound beam and inserted through the anesthetized skin and subcutaneous tissues toward the lesion to be biopsied. With proper alignment of the needle within the plane of the ultrasound beam, the entire length of the needle shaft should be visualized at all times ( Fig. 17-3 ). If the entire needle is not visible, some malalignment of the needle with the ultrasound beam exists ( Fig. 17-4 ). This can be corrected by rechecking the alignment of the needle with the central beam of the transducer. A slight jiggling or in-and-out motion of the needle helps visualize the needle ( Fig. 17-5 ). When experience is gained with sonographically guided freehand biopsy methods, this becomes a very rapid and reliable method of guiding biopsy needles to the target in question.

Sonographic guidance can be problematic in obese patients because the echogenic needle can be hard to visualize in the echogenic soft tissues. Lesions located within bones, or deep to bone or bowel, cannot be biopsied owing to lack of visualization of the lesion.

Computed Tomography

CT can be used to guide biopsy needles to virtually any area of the body. CT provides excellent visualization of the lesion to be biopsied and allows accurate identification of organs between the skin and the lesion. CT is particularly suited to guiding biopsy of deep lesions within the body such as retroperitoneal, pelvic, thoracic, and musculoskeletal lesions. The learning curve associated with CT-guided biopsies is generally shorter than that associated with sonographically guided biopsies, and it has therefore become a popular guidance modality. Scans through the region of interest are first performed with either a commercially available grid system (E-Z-EM, Westbury, N.Y.) or a homemade grid system placed on the patient’s skin. Commercially available grid systems contain multiple lead lines constructed in a grid pattern. Alternatively, a homemade phantom can be constructed by taping together approximately ten 15-cm lengths of 4- or 5-French catheters at 1-cm intervals. The homemade grid fulfills the same function as the commercially available systems.

On the CT image that gives the best view of the lesion, a safe access route is chosen and the distance to the lesion marked on the image. The patient is then brought to the table position where the biopsy is to be performed and the skin site marked using the grid on the patient’s skin and the centering laser light beam in the CT gantry. The needle is inserted to the predetermined depth and location. Scans are obtained at the level of the needle entry site to determine the location of the needle. The tip of the needle is readily recognized by a black streak artifact that occurs at the needle tip ( Fig. 17-6 ). If the needle is not in an appropriate position, further needles can be inserted and scanned (using the first needle as a guide for adjusting the trajectory of further needles) until an appropriate position within the lesion is obtained.

Compared to sonography, the lack of real-time visualization with CT guidance is a limiting factor. The recent introduction of CT fluoroscopy with multislice CT scanners has attempted to redress this balance. However, CT fluoroscopic units will undoubtedly make CT guidance a much more viable, albeit more expensive, option for biopsies.

Performing the Biopsy

Coaxial vs. Tandem Technique

Using the coaxial technique, a single needle is placed in the periphery of the lesion and a smaller, longer needle is placed through the initial needle to biopsy the lesion ( Fig. 17-7 ). Using the Turner biopsy needle system, a 23-gauge needle will pass through a 20-gauge needle and a 22-gauge through a 19-gauge. The coaxial technique has several advantages in that only one puncture is made into the organ, reducing the propensity for hemorrhage or other complications. Multiple tissue samples can be obtained through the first needle. Lastly, precise needle placement is required only for the first needle.

Using the tandem technique, a 22-gauge needle is placed into the lesion and used as a reference needle (see Fig. 17-7 ). This reference needle then stays within the lesion until the end of the procedure. Further needles are inserted in tandem to the reference needle and are placed to the same depth and follow the same trajectory as the reference needle. This technique is useful for CT-guided biopsies wherein multiple fine-needle samples can be obtained without precisely localizing each subsequent needle that is passed.

In the main, the coaxial and tandem techniques are primarily used with CT guidance. With real-time sonographic guidance, the author’s unit generally takes a sample with a single needle and guides subsequent needles into the lesion as required. Because of the flexibility of sonography and continuous real-time visualization, the tandem and coaxial techniques are rarely necessary. However, they are useful when using CT guidance so that further needle passes do not require precise CT monitoring, which is cumbersome and time consuming.