**5.1. Improved techniques for biopsy**

RTBs are performed percutaneously under local anesthesia. It can be with needle core biopsy or fine needle aspiration (FNA) with US or CT guidance.

Core needle biopsies yield a higher diagnostic rate and a more accurate histological examination over FNA. This was exemplified by a systematic review performed by Marconi et al. [17] (57 studies recruiting 5228 patients)—showing superior sensitivities and specificities over diagnostic FNAs. A coaxial technique allows multiple biopsies to be taken through a coaxial canula, avoiding potential tumor seeding. Comparing needle sizes used, 18-gauge needles are preferred over 14- and 20-gauge needles—showing safer and more accurate histological results [18, 19].

With regard to imaging modalities, US and CT possess their own merits. CT has the advantage of a better resolution that is ideal to locate lesions that are in proximity to critical structures. US has the advantage of lower radiation and lower cost. More importantly it allows real-time needle placement that is suited for nonfocal renal lesions [20].

In spite of acknowledging preferred techniques of RTBs, there are other technical factors that affect their success: amount of adipose tissue in the patient, echogenicity and location of lesion. The challenge of performing a successful biopsy can thus vary from lesion to lesion. Effective communication between the interventional radiologist and urologist is necessary to ensure that a RTB would be reliable in managing a specific SRM.

#### **5.2. Improvements in accuracy**

Recent literature lends support to the diagnostic accuracies of RTBs, challenging the notions some urologists believe. The meta-analysis performed by Marconi et al. [17] showed that initial RTBs yielded a diagnosis in >90% of cases. Core biopsies showed a high sensitivity and specificity of 99.1 and 99.7%, respectively. In cases where both a RTB and surgical pathology were available, good concordance (k = 0.683) for tumor histotype and fair concordance (k = 0.34) for tumor grade were shown.

A systematic review by Patel et al. [21] (including 20 studies with 2979 patients) showed a high diagnostic accuracy of RTB with a sensitivity of 97.5% and a specificity of 96.2%. There was also a high histological concordance observed. Patel's study highlighted the concern of a reasonable non-diagnostic rate (14.1%).

However, repeat biopsy led to diagnosis in 80% of previously undiagnostic biopsies. It is reported that following a non-diagnostic biopsy, a repeat biopsy has a high rate of rendering a diagnosis—ranging from 67 to 85% [22]. Therefore, in the case of a non-diagnostic biopsy, there is merit in performing a repeat biopsy.

With overall improved diagnostic accuracies of RTBs, urologists should be more reassured about their successes.
