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BIOPSY OVERVIEW

Image-guided needle biopsy is the mainstay for diagnosis of nonpalpable masses almost anywhere in the body. The indica-tions for biopsy continue to evolve, and although percutaneous biopsy of a given mass is possible, it may not be indicated (Thompson et al, 1985). As with any invasive procedure, percu-taneous biopsy has associated risks that should be weighed prior to the procedure. Needle biopsy is warranted when the result of the biopsy would potentially affect patient management. These indications include confirmation of preoperative diagnosis, doc-umentation of primary or metastatic disease in patients who are not surgical candidates, evaluation of organ dysfunction, and sampling for special studies such as receptor or gene mutation status.

Several methods are available to obtain tissue, including biopsy by percutaneous needle or by endoluminal and transve-nous techniques. Needles ranging in size from 25- to 14-gauge are typically used, and outside the central nervous system, a biopsy can be obtained from almost any abnormality that can be imaged. Most needles contain an inner stylet, which is removed when the needle is appropriately positioned, immedi-ately before obtaining the specimen; the stylet prevents the needle from coring interposed structures and accumulating nontarget material before optimal placement. Smaller “fine” needles (25 to 20 gauge) are used to obtain cytologic specimens or to obtain samples for culture or flow cytometry. Larger needles (19 to 14 gauge) are used to obtain tissue cores when histologic material is required for pathologic diagnosis or when special studies, such as immunohistochemical staining, are to be performed.

Common malignancies in which core specimens may be necessary for diagnosis include lymphoma, sarcoma, thymoma, and mesothelioma. Core material may also be required to diag-nose well-differentiated hepatocellular carcinoma (HCC) or benign hepatic tumors. Tissue cores also may be required for mutational analysis in patients for whom targeted therapies are being considered. In most cases, fine needle aspirates are suffi-cient, and multiple immunohistochemical stains can be used on a single sample, allowing for accurate cell typing.

To increase the likelihood of a diagnostic biopsy and to mini-mize complications, a high-quality imaging study should be available for review both when the biopsy is being planned and when it is performed. In some cases, careful review of imaging studies may provide a definitive diagnosis, obviating the need for biopsy. Review of preprocedure imaging also influences selection of the most appropriate modality for guidance and patient positioning during the procedure, so that potential problems such as interposed lung, bowel, or blood vessels may

be anticipated and avoided. In addition, knowledge of imaging findings allows for appropriate discussion of relevant risks in the informed consent. With proper preprocedure imaging, the biopsy can be planned to avoid unusual or unsustainable posi-tions, complex needle angulation, and challenging breathing instructions.

Review of imaging studies before biopsy also facilitates tar-geting of the most viable area of a mass. As large masses outgrow their blood supply, they become necrotic, and diagnostic mate-rial cannot be reliably obtained in a background of necrosis. Preprocedure contrast-enhanced computed tomography (CT), magnetic resonance imaging (MRI), and positron-emission tomography (PET) can allow for accurate targeting of areas most likely to yield a diagnostic specimen.

BIOPSY TECHNIQUE

Fine Needle AspirationA 25- to 20-gauge needle is advanced into the target lesion, and real-time (ultrasound, fluoroscopy, or CT fluoroscopy) or inter-rupted imaging (conventional CT or MRI) is performed to guide and assess needle position. Coaxial techniques are some-times useful but are generally unnecessary, but some operators are partial to this technique. Although coaxial biopsy requires the introduction of a larger needle than is used for biopsy, it has the advantage that multiple samples may be obtained without creating a new tract for each pass, and the tract can be emboli-zed or “plugged” to prevent hemorrhage in high-risk situtations (Billich et al, 2008).

Fine needles come in a variety of tip designs. Many physi-cians use a Chiba-style needle, in which the needle tip and inner stylet are beveled. Our preference is a Westcott-style needle: in addition to a beveled tip, it has a notch in the sidewall of the needle just proximal to the tip; this facilitates the operator’s ability to choose more precisely the location from which the cells will be aspirated.

When needle position has been confirmed, the needle is attached to a disposable syringe. The plunger of the syringe is retracted to apply suction as the needle is moved back and forth within the lesion to obtain a sample. The needle is with-drawn after suction is released, and the specimen is deposited on a glass slide. Smears are made from the biopsy specimen, and these may be used for immediate analysis (e.g., Diff-Quik) or fixed in ethanol for immunohistochemical stains. In some cases, molecular studies may need to be performed on fine needle specimens, and charged slides may be used that electrostatically attract tissue and bind it to the slide. The resid-ual material within the syringe and needle is rinsed in a

CHAPTER 20

Percutaneous biopsy

Anne M. Covey and Lynn A. Brody