ASCO GU 2018: Optimal Imaging for the Indeterminate Renal Mass on CT: How to Determine What is Indeterminate

San Francisco, CA ( The incidence of small renal masses (SRM) has increased significantly over the last 30 years due to the increased use of cross-sectional imaging. Although, we have experienced a staged migration towards lower stages, a significant decrease in kidney cancer mortality has not followed. The reason for this phenomenon is that most of the masses that have been increasingly diagnosed and treated are either being or indolent renal cell carcinomas (RCC). While advances imaging and risk stratification algorithms have helped reduce the over-treatment of benign masses such as mildly complex cysts and AMLs, there is a significant set of indeterminate masses that still undergo unnecessary treatment. 

Dr. Silverman, a professor of Radiology at the Brigham and Women’s Hospital, discusses current and emerging techniques that can be used to further characterize indeterminate renal masses in the hope to avoid over-treatment of benign renal masses or indolent tumors. The most important factor in the characterization of a renal mass is the performance of an adequate imaging study. A renal mass protocol CT consists of at least 30-42 grams of iodine bolus, thin sections (3mm), before and after IV contrast scanning which includes a nephrogenic phase at minimum, with a corticomedullary and excretory phase optimally.  In those in whom a contrasted CT scan is not possible, a renal mass protocol MRI should be considered which consists of a T1 and T2 sequence, with selective fat suppression, chemical shift and diffusion sequences, subtraction images and ideally with contrast administration. 

Dr. Silverman, warns about the over-treatment of AMLs (20%) which in most cases is related to the lack of non-contrast imaging or scans lacking thin sections were small foci of fat can be missed. AMLs that are lipid-poor can also be characterized with imaging as these masses tend to be homogenous and hyper-enhancing and can be easily characterized with a percutaneous biopsy. There is also value on short follow-up imaging especially for small irregular masses with heterogeneous enhancement, as some of these masses may represent focal pyelonephritis which resolves with time. Lastly, Dr. Silverman introduces several emerging nuclear medicine tracers which can better distinguish the different renal mass histologies. 99mTc-Sestamibi PET-CT, a test clinically used for detection of parathyroid adenomas was recently introduced as a potential tool for detecting mitochondria-rich tumors (chromophobe RCC and oncocytoma) with a sensitivity and specificity of 83.3% and 95.2%, respectively. Immuno-PET with G-250 using an iodine-labeled antibody against carbonic anhydrase IX (CA-IX), which is known to be over-expressed in ccRCC, exhibits near 90% sensitivity and specificity for this RCC subtype.

In summary, benign and indolent small renal masses remain over-treated in the US. Optimization of currently available imaging along with judicious use of percutaneous biopsy can help us minimize the over-treatment epidemic. Emerging nuclear medicine tracers have the potential for imaging histology identification avoiding the need for an invasive percutaneous biopsy. 

Presented by: Stuart G. Silverman, MD. Brigham and Women’s Hospital, Boston MA

Written by: Andres F. Correa, MD, Fox Chase Cancer Center, Philadelphia, PA at the 2018 American Society of Clinical Oncology Genitourinary (ASCO GU) Cancers Symposium, February 8-10, 2018 - San Francisco, CA