To minimize the risk of hemorrhagic complications from renal biopsy, patients are screened for hemorrhagic diathesis. Screening is warranted even in patients with no history of bleeding. In the United States, most radiologists (84 %) routinely obtain a screening history of potential hemostatic defects and have patients undergo relevant laboratory tests—81 % request prothrombin time, 78 % request partial thromboplastin time, and 59 % request platelet count [43]. At a minimum, a platelet count and international normalized ratio (INR) should be obtained. Patients are advised to stop taking aspirin and other antiplatelet agents 5–7 days prior to the procedure. Patients taking warfarin are asked to stop taking it 5 days prior to the procedure to allow the INR to return to an acceptable range. While anticoagulation agents are suspended, patients may be given heparin or low-molecular-weight heparin to bridge the gap until warfarin can be restarted. Continuous intravenous heparin infusion should be stopped at least 2 h prior to the procedure. Low-molecular-weight heparin (e.g., Lovenox) is suspended only on the day of the biopsy. Although a normal platelet count and normal INR are desirable, we have more liberal guidelines in our practice and perform renal mass biopsy in patients with platelet counts as low as 50,000 and INRs of 1.5.

Biopsy of a renal mass can be accomplished using ultrasonography [14, 44–46], CT [14, 29, 38, 44, 47], or MR [38, 48] imaging for guidance. Multiplanar imaging capability and real-time demonstration of the needle tip are major advantages of ultrasound guidance (Fig. 17.17). Because the perinephric fat and the needle are both echogenic, visualization of the needle as it is advanced to the kidney may be difficult under ultrasound guidance, and the utility of ultrasound is limited in obese patients. Also, tumors in the upper pole or medial aspect of the kidney are more difficult to image with ultrasound due to adjacent bowel and intervening lung. Although a nonsedated patient can cooperate with breathing exercises to provide a better window for imaging of the kidney and renal tumors, performing a renal biopsy with breath-hold in deep inspiration is challenging for both the patient and the operator. If patients are sedated during the procedure, it is less likely that they will be able to cooperate with breathing and long breath-hold instructions.

Alternatively, renal biopsies can be performed under CT guidance. Exophytic renal masses change the contour of the kidney and are easily detected with non-contrast CT (Fig. 17.18). Intraparenchymal tumors without an exophytic component may be more difficult to localize on non-contrast CT images if they are isodense with the kidney. In these cases, administration of iodinated contrast medium immediately prior to the biopsy helps delineate the margins of the tumor (Fig. 17.19). Hypervascular tumors such as RCC show intense arterial enhancement, but nearly all tumors become more hypodense than the normal kidney in the excretory phase of the examination. As the normal kidney continues to accumulate and excrete iodinated contrast medium, the difference in density remains perceptible for the duration of the biopsy, allowing targeting of the tumor. Anatomic structures such as intervening bowel and pleural space that may be hard to visualize on ultrasonography are readily visible on CT. A major drawback of CT guidance for renal mass biopsy is the intermittent nature of imaging in a single axial plane. It may be difficult to image the needle and the tumor in the same plane, particularly in cases of small tumors. Real-time CT fluoroscopy can alleviate some of these challenges but can also increase radiation dose to the patient and the operator. Ultrasonography and CT guidance can be combined to optimize targeting of renal tumors in difficult cases.

Renal tumors are particularly well suited for biopsy under MRI guidance if an interventional MRI suite is available. Renal tumors often demonstrate high signal intensity on T2-weighted images, allowing easy detection. Any number of imaging planes—such as axial, oblique axial, sagittal, or sagittal oblique—can be used to target the tumor using intermittent or real-time imaging (Fig. 17.20). MRI-compatible needles, constructed of nonferromagnetic alloys, are available for use within the magnetic field. There are no published reports directly comparing the diagnostic success rates of the different imaging modalities used in image-guided renal mass biopsy. Anecdotal reports indicate that diagnostic yield, sensitivity, or negative predictive value for image-guided renal mass biopsy is independent of the imaging modality [14, 49]. Most important, the imaging features of an individual mass along with the experience and personal preference of the operator help determine the most useful method of tumor localization and targeting.

Renal masses can be sampled both by fine-needle aspiration (FNA) and by tissue-cutting tip needles. FNA samples are obtained using 21-gauge or smaller needles, which are believed to minimize blood contamination of the sample and to yield a larger number of cells. Larger core biopsy samples are obtained using automated “biopsy guns” that are equipped with tissue-cutting tip needles. Both FNA and core biopsies can be performed through a coaxial guide or cannula [50]. Once the guiding cannula is advanced to the surface of the tumor, multiple samples can be obtained without reinserting the sampling needle through a new tract (Fig. 17.21). This technique decreases patient discomfort and shortens the procedure time. The coaxial technique helps avoid repeated contact of a needle that may be contaminated with tumor cells with the overlying abdominal or retroperitoneal tissues, thus reducing the potential risk of tract seeding. In addition, procoagulants or an absorbable gelatin sponge (Gelfoam) can be injected into the tract to promote hemostasis at the end of the procedure [49]. For most renal biopsies, an 18- to 16-gauge guide needle is used. With this approach, 22-gauge needles can be used in FNA biopsy, and 20- to 18-gauge cutting needles can be used in core biopsy.

Most renal mass biopsies are performed with the patient in a prone (Fig. 17.22), semiprone, or decubitus position. During ultrasound-guided biopsies, the patient can be rotated to an arbitrary oblique position to allow a better window to visualize the tumor or a safer tract for advancing the needle. For CT-guided procedures, an ipsilateral decubitus position helps decrease the volume of the dependent thoracic cavity, thus reducing the lung excursion in the caudal direction (Fig. 17.23). This position provides a safer approach to upper pole tumors and has a lower risk of pneumothorax (Fig. 17.24). Otherwise, the CT gantry may be tilted to allow an oblique axial plane of imaging to avoid traversing the lung base (Fig. 17.25). Occasionally, a large renal mass in a very thin patient can be approached laterally (Fig. 17.26) or anteriorly (Fig. 17.27) with the patient in the supine position. Small tumors in the anterior aspect of the kidney may warrant a lateral approach with the patient in the supine or prone position (Fig. 17.28). If an intercostal approach is needed, care must be taken to avoid injury to the neurovascular bundle that is often located along the inferior margin of the ribs. Transhepatic and transsplenic biopsy of renal masses may be considered if no other needle paths are available, but these approaches are rarely used (Fig. 17.29). Ideally, different areas of the tumor should be targeted to obtain a representative sample. Necrotic areas, usually encountered in the center of large tumors, should be avoided [51]. For tumors smaller than 4 cm, one central and one peripheral core biopsy is recommended, whereas for tumors larger than 4 cm with a potentially necrotic center, two peripheral core biopsies are recommended [51]. Core biopsy samples should be visually inspected to estimate their size and quality. Fragmented or small samples (<1 cm) warrant additional sampling of the tumor [32].

Some of the largest recent series of renal mass biopsy have reported very few or no major complications [14, 32, 44, 45, 52–54]. In a total of 362 biopsies, there were 17 minor complications (4.7 %) and 1 major complication (0.3 %). Potential complications for renal mass biopsy include perinephric hemorrhage, hematuria, arteriovenous fistula, infection, pneumothorax, and needle tract seeding.

Most renal tumors, particularly RCCs, are hypervascular and such are prone to bleeding after percutaneous biopsy. Small perinephric or subcapsular hematomas accompany these procedures in 44–91 % of cases but are often self-limited, do not cause any symptoms, and do not require additional intervention (Fig. 17.30) [47, 55]. Renal hemorrhage that necessitates hospital admission or blood transfusion occurs in 1–2 % of cases [33, 56]. Subcapsular hematomas are often asymptomatic (Fig. 17.31), but they can be large and may cause significant pain and severe hypertension [57]. Hematuria as a result of renal mass biopsy is also uncommon, but it may lead to ureteral obstruction and pain [58]. An arteriovenous fistula should be considered in cases of persistent bleeding [56, 59]. If careful attention is given to aseptic technique, the risk of infection is minimal. With the patient in the prone position, the posterior sulcus extends over the upper pole of the kidney in most patients. During CT-guided renal mass biopsy, transgression of the pleural space and/or lung may cause a pneumothorax [60, 61]. Placing the patient in an ipsilateral decubitus position or using a triangulation technique with subcostal needle insertion helps reduce the risk of pneumothorax [62].

For many years, percutaneous renal mass biopsy was considered inappropriate because of fear of needle tract seeding. Although occasional cases of tract seeding have been reported after percutaneous biopsy of renal tumors, the actual incidence is low. The overall estimated risk of needle tract seeding in urologic malignancies is less than 0.01 % [63], which is comparable to risk of this complication in other abdominal biopsies. In recent series of renal tumor biopsy, no case of needle tract seeding was reported [32, 33, 47, 52, 59, 64–69]. The lack of tract seeding in recent series may be related to the widespread use of the guiding cannula and coaxial technique during image-guided biopsy of renal tumors. It has been reported that urothelial carcinomas are at higher risk of seeding than are RCCs [63, 70], and some researchers have recommended that an infiltrative renal mass should not be biopsied unless lymphoma is a primary consideration [53]. However, we have found very little scientific evidence for this recommendation [70].

Large or persistent perinephric hemorrhage may cause a drop in hemoglobin levels and may cause symptoms related to blood loss. These symptoms often include one or more of the following: pain, hypotension, tachycardia, diaphoresis, weakness, and drowsiness. Transfusion of packed red blood cells may be warranted if the patient is symptomatic. If the bleeding persists, an angiogram and possible selective embolization may be warranted (Fig. 17.32) [71]. Gross hematuria, if self-limited and asymptomatic, does not require intervention. However, ureteral obstruction may require placement of a stent, preferably retrograde via cystoscopy rather than antegrade via percutaneous nephrostomy. Persistent hematuria should be evaluated by angiography to rule out a pseudoaneurysm or arteriovenous fistula. If the course of the needle is close to the base of the lung, observation and chest radiography are warranted after the biopsy. A small pneumothorax may be observed, but an enlarging pneumothorax may require chest tube placement.