Image-Guided Breast Intervention

Indications

Minimally invasive image-guided breast biopsy is now the standard of care for the diagnosis of palpable breast lumps and for nonpalpable radiologically detected abnormalities. The diagnostic accuracy of needle biopsy is comparable to open surgical excision, and compared to surgical excision, imaged-guided biopsy has many advantages ( Box 23-1 ). In patients with a benign diagnosis, image-guided biopsy negates the need for surgery, and in patients with malignancy, preoperative diagnosis allows the patient to have one definitive surgery.

Before biopsy, the lesion should be fully worked up (which may include mammographic additional views and ultrasound), and all relevant imaging should be interpreted by a breast radiologist. Correlation should also be made with clinical examination to ensure the lesion being targeted corresponds to any palpable abnormality. The lesion should be assigned a BI-RADS category (or RCR category in the United Kingdom and Ireland) to determine the level of suspicion for malignancy ( Box 23-2 ). In general, BI-RADS lesions 4 and 5 warrant a biopsy (RCR lesions 3-5 are biopsied). For suspicious lesions, the radiologist should look for multifocal, multicentric, and contralateral disease. If the imaging appearances are suggestive of multifocal or multicentric disease, a second site of disease should be biopsied.

Contraindications

Before biopsy, patients are asked if they are taking anticoagulant or antiplatelet therapy. If taking warfarin, the latest international normalized ratio (INR) should be obtained (preferably within 5 days). All patients are then informed of the potential risk for bleeding, bruising, and hematoma formation and that this risk is greater for patients on antiplatelet or anticoagulant medication. However, due to the easy compressibility of the breast, most radiologists now perform biopsies in patients on aspirin and warfarin if the INR is less than 2.5 (some institutions use an INR of 4.0 as a cutoff for core biopsies and 2.5 for vacuum-assisted biopsies). Studies have shown that there are no significant complications in patients undergoing core needle biopsy on aspirin or warfarin. For patients on Plavix, the risk of discontinuing the drug must be balanced against the risk of hematoma formation, which is greater than in patients on aspirin.

Contraindications specific to each imaging modality are discussed in subsequent sections.

Complications

Significant complications (hematomas requiring drainage or infection requiring drainage or antibiotic therapy) have been reported in fewer than 1% of breast biopsies. The most significant risk related to bleeding during needle biopsy is related to obscuring the lesion, thus leading to possible sampling error.

For ultrasound-guided biopsies, there is a theoretical risk of pneumothorax if too vertical an approach is used. However, this should never occur if an appropriate technique is adopted and the needle is kept parallel to the chest wall at all times.

The postbiopsy care and instructions are the same for all biopsies, although the risk of bruising is increased with larger gauge vacuum-assisted biopsies and in patients on anticoagulants. Manual pressure is applied to the biopsy site and skin incision for 5-10 minutes or until hemostasis is achieved. A compression dressing and ice pack may be applied in patients with large hematomas or those on anticoagulants.

General Principles

Clip Placement

Metallic biopsy marker clips are increasingly being placed at the time of image-guided biopsy to mark the biopsy site ( Box 23-3 ). In general a clip is placed if the biopsied lesion may be difficult to visualize on repeat imaging due to small size or subtle appearance, or when the target is completely excised at biopsy. A clip may also be placed for correlation across imaging modalities, that is, to confirm that a lesion biopsied at ultrasound corresponds to a mammographic abnormality ( Fig. 23-1 ). Clips should also be placed in patients undergoing neoadjuvant chemotherapy in case the tumor shrinks and cannot be subsequently visualized for needle localization ( Fig. 23-2 ). In these patients, clip placement is also helpful to identify the tumor bed at histopathology. Finally, clips should be placed at magnetic resonance imaging (MRI)-guided biopsy to allow for wire-guided localization and excision in case of an abnormal result.

Box 23-3

Indications for Clip Placement

• Small lesions

• Lesions with subtle appearance

• Complete excision of the target at biopsy

• Correlation across imaging modalities

• Patients undergoing neoadjuvant chemotherapy

• Magnetic resonance imaging–guided biopsies

Most clips are made of titanium or stainless steel and are preloaded in a sterile disposable introducer, which is inserted under image guidance to the target location. When the needle is in satisfactory position, the marker clip is deployed by depressing a plunger; most introducers have a safety switch to prevent inadvertent deployment. For ultrasound-guided clip placement, the introducer needle is introduced under direct sonographic guidance using the same technique as for core biopsy so that the tip of the introducer lies centrally within the targeted lesion. Most vacuum-assisted biopsy devices have compatible preloaded clip introducers that are inserted through the biopsy device or coaxial sheath.

Many clips now available are embedded in cylindrical plugs of polymer material or collagen to inhibit clip migration and can be easily visualized under ultrasound, thus facilitating ultrasound localization. Clips are available in a variety of shapes and if multiple lesions are present, placement of markers of different shapes should be performed to distinguish between biopsy sites. MRI compatible clips are also available.

Automated Spring Loaded Core Biopsy Devices

Automated spring loaded core biopsy devices are the needle of choice for ultrasound-guided procedures. In general, the larger the gauge, the greater the diagnostic accuracy and needles smaller than 14 gauge should not be used. These needles consist of an inner stylet with a trough that collects the sample and an outer cutting cannula ( Fig. 23-3 ). They ideally produce a core of tissue 1-2 cm in length and 1-2 mm in width. When deployed the inner stylet moves forward at high velocity, the tissue falls into the trough, and the cutting cannula then moves forward at high speed to cover the trough ( Fig. 23-4 ). The needle can then be withdrawn. The tissue sample is retrieved by retracting the outer cutting cannula and exposing the trough containing the tissue sample.

Vacuum-Assisted Biopsy Devices

Vacuum-assisted biopsy needles use vacuum suction to pull the target tissue into the central aperture, which collects the samples. They remove larger volumes of tissue, leading to improved diagnostic accuracy and lower rates of underestimation of atypical ductal hyperplasia (ADH) and ductal carcinoma in situ (DCIS), and are the needle of choice for stereotactic-guided and MRI-guided biopsies ( Tables 23-1 and 23-2 ). Handheld vacuum-assisted devices may also be used under sonographic guidance but do not confer any diagnostic benefit. However, these devices do generate larger core samples and some operators use these devices to excise small benign lesions under sonographic guidance (see Breast Lesion Excision Systems).

A number of high-quality vacuum-assisted devices are approved for clinical use, many of which are MRI compatible. These include Mammotome (Johnson and Johnson Ethicon Endo-Surgery Inc, Cincinnati, Ohio), Encor (C.R. Bard, New York, N.Y.), and Suros ATEC and Eviva (Suros Surgical Systems Inc, Indianapolis, Ind.). Vacuum-assisted biopsy devices are available in 8-14 gauge, and while diagnostic accuracy improves when changing from an automated spring-loaded core biopsy needle to a vacuum-assisted device, there is no significant decrease in underestimation rates with increasing needle gauge.

Selection of which needle to use depends on operator and institution preference. Some of these needles adopt a coaxial approach whereby an introducer sheath and stylet are first inserted and the biopsy needle is subsequently placed through the introducer. Other biopsy devices allow for a single direct insertion of the biopsy probe. Most devices are available with a variety of probe lengths and in both standard and petite (shorter biopsy chamber) sizes to allow for biopsy of lesions in smaller breasts. The needle is positioned in the breast so that the aperture is at the center of the target lesion. When vacuum suction is applied, the tissue is aspirated into the aperture and a rotating cutter is then advanced forward and the sample captured. Most vacuum-assisted devices have a built-in sample collection chamber that allows for capture of multiple samples without withdrawing the needle. Different parts of the same lesion are sampled by rotating the direction of the aperture through 360 degrees. If the biopsy device lies to one side of the lesion, sampling can be concentrated in the direction of the lesion. When sampling is complete, saline lavage can be performed to irrigate the biopsy cavity to minimize hematoma formation. Most devices also allow for direct instillation of local anesthesia through the device during tissue sampling to minimize pain during the procedure. Vacuum-assisted devices allow for direct clip placement through the biopsy device or coaxial introducer sheath for accurate clip positioning in the biopsy bed.

See Box 23-4 for advantages of vacuum-assisted devices.

Breast Biopsy Reports

Box 23-5 highlights the pertinent information to include in breast biopsy reports.

Selection of Imaging Modality

Biopsy may be performed under sonographic, stereotactic, or MRI guidance. Recently systems to biopsy lesions under positron emission mammography (PEM) and breast-specific gamma imaging (BSGI) guidance has become commercially available.

In general, breast lesions should be biopsied using the modality with which they are best visualized. Before biopsy, the radiologist should review all of the relevant imaging to ensure that the most appropriate modality is used. However, selection of imaging modality also depends on patient factors such as comfort and mobility, on operator preference and experience, and on cost and equipment availability.

Ultrasound-Guided Biopsy

Technique

A high-frequency linear array transducer of at least 10 MHz should be used for the procedure. The patient is positioned supine in a slightly oblique position with the side to be biopsied slightly elevated and the ipsilateral arm over her head. A wedge cushion can be placed behind the patient’s shoulder to support her in this position. If possible the patient and ultrasound machine should be positioned so that the patient lies between the operator and the ultrasound screen so the breast lesion, needle, transducer, and screen are all in the operator’s direct line of vision. This ensures that the lesion and needle are visualized at all times and avoids the need for the operator to perform uncomfortable twisting movements.

The biopsy needle should be inserted into the breast, keeping the needle parallel to the chest wall and transducer at all times to avoid the potential for pneumothorax. Firm pressure should be maintained on the lesion with the transducer to stop it from moving. This is especially important in the case of fibroadenomas, which can be very mobile. The long axis of the needle and especially its tip should be visible along the long axis of the transducer during the entire procedure. Before firing the automated needle, the operator should be satisfied with the position. After firing, an image of the needle within the lesion should be recorded to document accurate sampling. If necessary, an orthogonal view can be obtained by rotating the transducer 90 degrees to confirm needle placement in the lesion by visualizing the echogenic dot of the needle ( Figs. 23-5 and 23-6 ). The number of cores obtained depends on the adequacy of the samples but in general two or three good samples should suffice. If the targeted lesion contains calcifications, then a specimen radiograph may be obtained. See Figure 23-3 .

Postbiopsy care is as standard for all breast biopsies.