MRI as a tool to assess surgical margins and pseudocapsule features directly following partial nephrectomy for small renal masses

Purpose: To evaluate the feasibility of ex vivo 7T MRI to assess surgical margins (SMs) and pseudocapsule (PC) features after partial nephrectomy (PN).

Materials and methods: In this prospective, IRB-approved study, seven patients undergoing a PN for nine tumours between November 2014 and July 2015 were included for analysis after obtaining informed consent. MRI of the specimen was acquired using a 7T small bore scanner. The imaging protocol consisted of anatomical T1-, T2- and diffusion-weighted imaging. After formalin fixation, specimens were cut for pathology work-up in the same orientation as the MR images were obtained. The entire specimen was processed into H&E slides that were digitally scanned, annotated and correlated with radiological findings for negative SMs, PC presence, PC continuity and extra-PC-extension (EPCE). Sensitivity and specificity of MRI for assessment of these endpoints were calculated.

Results: The sensitivity and specificity for assessment of the SM were 100% and 75%, respectively. Two false-positive outcomes were reported, both in case of EPCE and a SM ≤0.5 mm. For the presence of a PC, sensitivity and specificity were 100% and 33%, respectively. Two false-positive scans with anatomical structures mimicking the presence of a PC occurred. If a PC was present, continuity and EPCE were assessed with a sensitivity and specificity of 75% and 100% and 67% and 100%, respectively.

Conclusion: Ex vivo 7T MRI is a feasible tool for perioperative evaluation of SMs, and if present, PC features after PN. This may facilitate maximal sparing of renal parenchyma without compromising oncological outcomes.

Key points: • Ex vivo MRI may contribute to improvement of negative surgical margins during partial nephrectomy. • Due to the assessment of surgical margins within a limited time span from obtaining the partial nephrectomy specimen, surgery for more complex tumours is possible with maximum sparing of healthy renal parenchyma without compromising oncological outcomes. • The intra operative assessment of pseudocapsule continuity along the resection margin enables maximal sparing of healthy renal parenchyma without delayed diagnosis of incomplete resection.