Optimal diagnostic criteria for lateral lymph node dissection using magnetic resonance imaging: a multicenter prospective study.

BACKGROUND: LLND in cases with suspected lateral lymph node (LLN) metastasis has been focused on as a novel treatment strategy in recent years. However, the optimal indication for LLND in rectal cancer patients has not been determined. This study aimed to establish the optimal indication for lateral lymph node dissection (LLND) in patients with rectal cancer using magnetic resonance imaging (MRI). METHODS: A total of 209 patients with rectal adenocarcinoma who underwent total mesorectal excision and LLND in 13 hospitals were prospectively registered. By matching the sizes of the harvested LNs and those in magnetic resonance imaging (MRI), the pathological outcome of each LN was confirmed one-by-one. Using parameters of the LLNs in MRI, the optimal diagnostic criteria for LLND were established. RESULTS: Of 3241 harvested LLNs, including 83 metastatic nodes, 1010 (31.1%) were visualized on MRI. Although all parameters assessed showed strong correlations with the presence of metastasis, none of these parameters could discriminate metastatic LLNs from non-metastatic nodes with sufficient sensitivity. However, by using the combination of long axis and short/long ratio in pretreatment MRI, we could establish optimal criteria for LLND. The sensitivity and specificity of the criteria for LLN metastasis were 94.3% and 40.2%, respectively. CONCLUSIONS: In conclusion, we established novel criteria for LLND in rectal cancer patients using MRI. Our criteria will be of great clinical use in determining indications for LLND.