Agreement of axial T2-MRI versus Contrast-Enhanced CT for solid renal mass active surveillance

Active surveillance (AS) of small renal masses (SRMs) typically relies on contrast-enhanced CT for serial size measurement. Non-contrast (NC) MRI protocols may provide an alternative. To assess the agreement of maximum axial tumor diameter and tumor nearness between NC MRI and contrast-enhanced CT for SRM surveillance, and to compare diagnostic confidence in tumor delineation across modalities.

We retrospectively identified 50 patients (mean age, 62.9 years; 44% women) who underwent both contrast-enhanced CT and axial T2-weighted MRI within 3 months as part of AS protocol. Nine radiologists from five hospitals independently assessed maximum tumor diameter (axial plane) and tumor nearness to the collecting system (TN, three-tier scale) and subjectively graded their diagnostic confidence in delineating the tumor contour (DC, 5-point scale) in 50 CT and MRI scans across four randomized reading sessions. Observer agreement for diameter assessment was quantified using the limits of agreement with the mean (LOAM), whereas TN and DC were analyzed using Gwet's AC2.

Mean tumor diameters were 19.9 mm for CT and 19.5 mm for MRI (mean difference, 0.4 mm; p = 0.051). Reproducibility LOAMs were ± 2.9 [2.7-3.2] mm (CT) and ± 3.1 [2.9-3.4] mm (MRI), with overlapping confidence intervals. TN ratings and agreement were similar for CT and MRI (p = 0.61; p = 0.86, respectively), whereas DC ratings were higher and interobserver agreement was better for CT (p < 0.001 and p = 0.009, respectively)..

NC axial T2-weighted MRI demonstrated tumor diameter agreement comparable to contrast-enhanced CT, along with comparable TN ratings and agreement, whereas CT yielded higher DC and better interobserver agreement for DC.