Whole-lesion diffusion metrics for assessment of bladder cancer aggressiveness

To explore associations of whole-lesion histogram diffusion metrics with pathologic findings and subsequent metastatic disease in bladder cancer patients undergoing radical cystectomy.

Twenty-three bladder cancer patients (21M, 2F; mean 70 ± 11 years) underwent MRI before cystectomy. A volume-of-interest was placed on all slices on the ADC map encompassing each lesion. Whole-lesion mean, kurtosis, and skewness of ADC were calculated and compared with T stage and pelvic nodal status at cystectomy and with subsequent metastasis in 20/25 patients with available follow-up.

At cystectomy, 39 % (9/23) were stage T2, 61 % (14/23) ≥T3, and 28 % (5/23) exhibited positive nodes; 35 % (7/20) developed later metastases. Mean ADC was significantly lower in stage ≥T3 than in lower stage tumors (1.20 ± 0.36 × 10(-3) vs. 1.55 ± 0.36 × 10(-3) mm(2)/s; p = 0.044), but showed no association with nodal or metastatic disease (p = 0.362-0.709). Kurtosis was significantly lower in tumors with, compared to without, nodal disease (-0.05 ± 0.29 vs. 0.91 ± 1.16; p = 0.037), and showed a non-significant decrease in tumors with, compared to without, later metastases (0.23 ± 0.63 vs. 0.83 ± 0.89; p = 0.088). Kurtosis was not associated with T stage (p = 0.811), and skew was not associated with any outcome (p = 0.516-0.643). Mean ADC achieved highest AUC for identification of stage ≥T3 (AUC = 0.754 vs. 0.516-0.643 for other metrics). Kurtosis achieved highest AUC for nodal disease (AUC = 0.811 vs. 0.522-0.556 for other metrics) and metastases (AUC = 0.736 vs. 0.516-0.626 for other metrics). Only difference in AUC between skewness and kurtosis for nodal disease was significant (p = 0.031).

While requiring larger studies, kurtosis has potential to complement mean ADC in bladder cancer prognosis using whole-lesion histogram analysis.