AUA 2017: Utility of preoperative MRI in characterizing the parenchymal-tumor interface of renal masses prior to surgical intervention

Boston, MA ( As primary RCC is increasingly identified on radiographic imaging, and as imaging modalities continue to improve, we continue to learn more about how these modalities can help guide our management and help predict outcomes.

In this single-institution, retrospective study of 43 patients with small renal masses undergoing robotic partial nephrectomy following an abdominal MRI, the authors correlate radiographic findings with surgical outcomes, specifically the risk of positive surgical margins. As this is an important clinical outcome during partial nephrectomy, and as MRI becomes more common, this study provides some basic initial knowledge regarding its utility.

In this study, the MRI was reviewed by a Urologic Oncologist in all cases. The urologic oncologist then graded the psuedocapsule according to a scale they developed called the i-Cap score. Of note, 26 underwent enucleation and 17 underwent partial nephrectomy. 88.4% were RCC on final pathology.

Of the 43 patients, 14 were cystic masses and 29 were solid renal masses. For both categories, they identified the MRI phase that best exposed the parenchymal-tumor interface (PTI). A traditional hypointense band on T2 Haste/SSFSE was characteristic in most of the cystic masses (13/14), while patients with solid masses exhibited a pseudocapsule best seen on either T2 post-contrast scans (15/29) or T2 Haste/SSFSE (14/29). A capsule was seen in all the patients, but it was circumferential in 76.7% of cases. A smooth PTI was seen in 36 cases, but 3 patients had evidence of infiltration on MRI. In terms of outcomes, 2 of those 3 with pre-operative infiltration on MRI had positive surgical margins (PPV 66%). Two of three patients had had standard partianl nephrectomy, while one had enucleation.

Limitations / Discussion Points:
1. Nature of partial nephrectomy – the majority of the patients had enucleation, which makes it a little more different to comment on positive surgical margin status. Ideally, standard partial nephrectomy or partial nephrectomy would be ideal.
2. Width of the PTI not indicated – this would be useful information for planning for surgical margins needed at the time of the partial nephrectomy.
3. How does it change management? – the authors do not specifically comment on this, but it is likely to early to make any conclusion.
4. As 12% were not RCC at the time of final resection, how could surgical margin status be assessed? This was not made clear.

While the authors conclude that an MRI is useful in delineating the PTI, this is very clearly an early experience, retrospective study. Of 200 eligible robotic partial nephrectomies, only 40 had pre-operative MRI – likely contributing to a selection bias.

Presented by: Arpeet Shah

Co-Authors: Shalin Desai, Connor Snarskis, Mara Hehemann, Kristin Baldea, Gopal N. Gupta

Written By: Thenappan Chandrasekar, MD, Clinical Fellow, University of Toronto
Twitter: @tchandra_uromd

at the 2017 AUA Annual Meeting - May 12 - 16, 2017 – Boston, Massachusetts, USA