The Usefulness of Diffusion MRI in Detection of Lymph Node Metastases of Colorectal Cancer

The aim of this study was to assess the sensitivity and specificity of preoperative diagnosis by diffusion magnetic resonance imaging (D-MRI) for lymph node metastasis of colorectal cancer. The b-value represents the diffusion factor (measured in s/mm(2)) and the strength of the diffusion gradients. The b-value used in this study was 1,000 s/mm(2). A total of 119 patients underwent D-MRI before resection of primary colorectal cancer (52 of the rectum, 67 of the colon) at our hospital between February 2005 and April 2006. Lymph node metastases judged by D-MRI were compared with postoperative pathological results. The form of lymph node metastasis was classified either as abundant or scarce type. The predictive values for lymph-node metastasis (sensitivity and specificity) by D-MRI were calculated from the result of this classification and lymph-node size. The study was divided into two periods: before the consensus meeting in January 2006, (n= 79) (P-I), and after the adjustment of the criteria to improve the sensitivity and specificity based on the results of P-I (n= 40) (P-II). Detection of lymph node metastasis using D-MRI in P-I had sensitivity of 61%, specificity of 73%, positive predictive value (PPV) of 55%, and negative predictive value (NPV) of 77%, while in P-II, these values improved to 79%, 95%, 94%, and 83%, respectively. Specificity and PPV for P-II were significantly higher than those for P-I (p< 0.05). The diameter of lymph nodes judged to be metastatic on D-MRI (P-I vs. P-II: n= 32 vs. 16) was 10.3 +/- 5.4 (3-28) vs. 9.1 +/- 3.0 (4-14) mm; 11.5 +/- 6.2 (4-28) vs. 9.2 +/- 3.1 (4-14) mm for truly positive nodes (n= 18 vs. 15), and 6 +/- 3.8 (3-14) vs. 8 mm for false-positive nodes (n= 14 vs. 1). On the other hand, lymph nodes judged negative by D-MRI (n= 47 vs. 24) was 5.9 +/- 2.4 (3-16) vs. 5.7 +/- 2.8 (2-15) mm; 5.9 +/- 2.1 (3-16) vs. 5.3 +/- 2.1 (2-8) mm for truly negative (n= 36 vs. 20), and 5.7 +/- 2.7 3-12) vs. 7.8 +/- 4.9 (4-15) mm for false negative (n= 11 vs. 4). As to the form of metastasis, all truly positive nodes were of the abundant type, and 6/11 (55%) in P-I and 1/4 (25%) in PII false-negatives were of the scarce type. In conclusion, D-MRI seems useful for preoperative detection of metastatic lymph nodes in colorectal cancer, especially if the node is hyperintense and more than 9 mm in diameter.