Quantitative sodium-MRI detects differential sodium content in benign vs. malignant oncocytic renal tumours

Abstract

AbstractBackgroundAccurate non-invasive subtyping of localised kidney tumours is an unmet clinical question in uro-oncology. Differentiation of benign renal oncocytomas (RO) from malignant chromophobe renal cell carcinomas (chRCC) is not possible using conventional imaging. Despite the importance of renal function for sodium regulation, little is known about sodium handling in kidney tumours.PurposeHere we used non-invasive sodium MRI (23Na-MRI) to quantify sodium concentration and relaxation dynamics across a range of different kidney tumour subtypes and have correlated these findings with imaging surrogates for perfusion, hypoxia, and cellularity.Materials and MethodsBetween January and April 2023, patients with localised renal masses were prospectively recruited and underwent23Na and proton (1H) MRI at 3T to acquire 3D maps of B1, total sodium concentration (TSC), proton and sodium relaxation rates (R2*), and diffusion weighted imaging (DWI). Statistical analysis included comparison and correlation of quantified imaging parameters across kidney tumour subtypes.ResultsTen patients were included in the final analysis (mean age±S.D. = 64±8 years; 7:3 male:female ratio) encompassing seven ROs, two chRCCs, two clear cell RCCs (ccRCC), and one papillary RCC (pRCC). The TSC was significantly higher in the ROs compared to the chRCCs: 162±58 mM vs. 71±2 mM (P< 0.05). The mean TSC in ccRCC was 135±59 mM, and 81 mM in pRCC. The23Na-derived and1H-derivedR2* values showed a weak correlation (Spearman r = 0.17;P= 0.50). There was a significant inverse correlation between TSC and1H-R2* (Spearman r = -0.39,P< 0.05), but TSC was independent of the DWI-derived imaging parameters.Conclusion23Na-MRI detected markedly different sodium concentrations within benign ROs and malignant chRCCs. In addition, the sodium signal inversely correlated with1H-R2* as a surrogate for hypoxia. Therefore we have shown the feasibility and potential of23Na-MRI for future research in renal tumours.Key results23Na-MRI was used to non-invasively assess kidney tumour subtypes for the first time.A significantly higher total sodium concentration was detected in benign renal oncocytoma (162±58 mM), compared to chromophobe renal cell carcinoma (71±2 mM), as the malignant counterpart:P< 0.05.Total sodium concentration showed a significant inverse correlation with1H-R2* (Spearman r = -0.39,P< 0.05), but it was independent of the diffusion-weighted imaging-derived parameters.Summary statement23Na-MRI showed potential for differentiating benign and malignant masses, to characterise kidney tumours, which may be linked to the underlying differences in deoxygenation as measured with1H-MRI.