DWI for Assessment of Rectal Cancer Nodes After Chemoradiotherapy: Is the Absence of Nodes at DWI Proof of a Negative Nodal Status?

OBJECTIVE. When considering organ preservation in patients with rectal cancer with good tumor response, assessment of a node-negative status after chemoradiation therapy (CRT) is important. DWI is a very sensitive technique to detect nodes. The study aim was to test the hypothesis that the absence of nodes at DWI after CRT is concordant with a ypN0 status. MATERIALS AND METHODS. A retrospective study was performed of 90 patients with rectal cancer treated with CRT followed by restaging MRI at 1.5 T, including DWI (highest b value, 1000 s/mm(2)). Two independent readers counted the number of nodes visible in the mesorectal compartment on DW images obtained after CRT. The number of nodes on DWI (0 vs >= 1) was compared with the number of metastatic nodes at histopathology or long-term clinical follow-up (yN0 vs yN-positive status). RESULTS. Seventy-one patients had a yN0 status, and 19 had a yN-positive status. For 10 patients, no nodes were observed at DWI, which was concordant with a yN0 status in 100% of cases. In the other 61 patients with a yN0 status, the median number of nodes detected at DWI was three (range, 1-17 nodes). To differentiate between yN0 and yN-positive status, sensitivity was 100%, specificity was 14%, the positive predictive value was 24%, and the negative predictive value was 100%. CONCLUSION. Although the absence of nodes at DWI is not a frequent finding, it appears to be a reliable predictor of yN0 status after CRT in patients with rectal cancer. DWI may thus be a helpful adjunct in assessing response after CRT and may help select patients for organ-saving treatment.