Biopsies can be performed under ultrasound, CT, or MRI guidance. The choice of the imaging guidance depends on the operator’s experience and habits, on tumor size and location, and on patient’s habitus. MRI is rarely used for the high costs and the need of ferromagnetic needles. Ultrasound guidance is used in most cases, since it allows a real-time puncture, avoids radiation exposure, and is associated with lower costs (Fig. 13.2). However, in some obese patients, CT guidance should be preferred, since the presence of significant subcutaneous and perivisceral fat can hinder a clear ultrasound visualization of the renal mass, which is essential to perform an accurate biopsy. Renal masses located at the upper pole or on the anterior face of the kidney and smaller than 15 mm in size are also more likely to be sampled under CT guidance (Fig. 13.3). A major limitation of CT guidance is that it does not allow biopsies in real time. This can be overcome with the use of modern techniques such as CT fluoroscopy.

At present there is no solid evidence of the superiority of the ultrasound or CT guidance. In a large series of biopsies of SRMs performed at the University of Toronto, no significant difference was observed between the detection rates of biopsies performed with the two approaches [19, 20].

Biopsies are usually performed with a Tru-Cut 18-gauge needle loaded on an automatic biopsy gun, which achieves the best compromise between safety and detection rate (Fig. 13.4a). The biopsy is generally performed coaxially to a 17-gauge cannula which is previously placed near or just inside the renal mass (Fig. 13.4b). The use of full-core needles seems to allow better results both in terms of diagnostic rate and accuracy.

Fine-needle aspiration (FNA) for cytology is performed instead with smaller (≤21 G) needles.

The patient is generally placed in a lateral decubitus, but a prone or semiprone position can be also used based on the characteristics of the renal lesion and on the selected imaging guidance. After performing local anesthesia, the most appropriate biopsy track is chosen, and a guided cannula is inserted percutaneously to approach the lesion (Fig. 13.5).

The puncture can be performed “freehand” or with the use of an ultrasound guide that directs the needle in a predetermined angle within the plane of view of the transducer (Fig. 13.6). The freehand technique requires more experience, but has the advantage of greater flexibility by allowing subtle adjustments that can compensate for improper needle trajectory and patient movement.

Once the lesion is reached, the stylet is removed, and the needle core biopsy or FNA is performed through the guiding cannula (Fig. 13.7). The biopsy can be performed after removal of the ultrasound guide or under real-time ultrasound guidance based on operator’s preference. Multiple biopsies can be obtained through the guiding cannula which is finely repositioned within the lesion to allow sampling of different areas of the tumor. This technique is called “coaxial” and is useful to reduce the risk of tumor seeding along the needle track, since it minimizes the potential risk of contact of the needle with the healthy tissues interposed between the skin surface and the renal mass.

When a FNA is planned together with a core biopsy, it should be performed first to limit the risk of hemorrhagic contamination of the sample, which makes the cytological diagnosis more challenging. The quality of the FNA sample should be checked by a cytologist during the procedure (Fig. 13.8). This increases the diagnostic yield and confirms the proper placement of the cannula through which the core biopsies will be then performed.

At present, the ideal biopsy pattern to sample renal masses of different sizes is not standardized. However, at least two good quality samples should be always obtained from different areas of the tumor, avoiding areas of necrosis. A good quality core is at least 1 cm long and not fragmented. Wunderlich et al. observed a poorer diagnostic accuracy for central biopsies in tumors >4 cm, likely due to the higher likelihood of necrosis in the central portion of larger tumors [21]. Based on these results, it is currently generally recommended to obtain at least a central and a peripheral core in <4 cm tumors and two peripheral cores in larger tumors.

To favor an optimal histological assessment, every biopsy should be placed between two sponges in a single histological cassette (Fig. 13.9).

Patients should be monitored for at least 4 h after the biopsy. The vital parameters and a cell blood count should be assessed. Post-procedural ultrasound and CT scans are generally not required in the absence of clinical or laboratory signs of active bleeding.

Complications after renal tumor biopsy are infrequent with the use of proper biopsy techniques and are mainly represented by immediate or delayed bleeding, since renal tumors are generally hypervascularized. However, significant bleedings requiring hospitalization and/or blood transfusion are rare in experienced centers (<1 %) [1].

The risk of tumor seeding along the needle track is anecdotal. Only seven cases of seeding of renal parenchymal tumors have been reported to date in the literature. Most of these cases were observed before 2001 when the biopsy was performed with different instruments and techniques [22]. The use of the coaxial technique is particularly important to avoid tumor seeding. In fact, the only case of seeding that has been recently described was not carried out with a coaxial technique [23].

Other possible rare complications of biopsy are pneumothorax in case of biopsies of upper polar lesions with a posterior approach and infections [24].

Renal tumor biopsy has been shown to have a good diagnostic rate (78–97 %) and a high specificity (98–100 %) and sensitivity (86–100 %) for the diagnosis of histological malignancy in several large series from experienced centers [1].

A recent systematic review and meta-analysis of the literature observed that the overall median diagnostic rate of renal tumor biopsy is 92 %. The sensitivity and specificity of diagnostic core biopsies and FNAs were 99.1 % and 99.7 % and 93.2 % and 89.8 %, respectively [25].