Local recurrence of renal cell carcinoma after partial nephrectomy: applicability of the apparent diffusion coefficient of MRI as an imaging marker - a multicentre study.

Purpose: The goal of the study was an assessment of the diagnostic performance of diffusion-weighted images (DWI) and apparent diffusion coefficient (ADC) of magnetic resonance imaging (MRI) in distinguishing local recurrence (LR) of renal cell carcinoma (RCC) from benign conditions after partial nephrectomy.

Material and methods: Thirty-nine patients after partial nephrectomy for solid RCC were enrolled in the study. Patients were followed up using MRI, which included DWI sequence (b = 800 s/mm²). All patients with MRI features of LR were included in the main group (n = 14) and patients without such features - into the group of comparison (n = 25). Apparent diffusion coefficient (ADC) values of suspicious lesions were recorded. In all patients with signs of locally recurrent RCC, surgical treatment was performed followed by pathologic analysis.

Results: The mean ADC values of recurrent RCC demonstrated significantly higher numbers compared to benign fibrous tissues and were 1.64 ± 0.15 × 10^-3 mm²/s vs. 1.02 ± 0.26 × 10^-3 mm²/s (p < 0.001). The mean ADC values of RCCs' LR and benign post-op changes in renal scar substantially differed from mean ADC values of healthy kidneys' parenchyma; the latter was 2.58 ± 0.05 × 10^-3 mm²/s (p < 0.001). In ROC analysis, the use of ADC with a threshold value of 1.28 × 10^-3 mm²/s allowed us to differentiate local recurrence of RCC from benign postoperative changes with 100% sensitivity, 80% specificity, and accuracy: AUC = 0.980 (p < 0.001).

Conclusions: The apparent diffusion coefficient of DWI of MRI can be used as a potential imaging marker for the diagnosis of local recurrence of RCC.