Diffusion-weighted magnetic resonance imaging for detecting lymph node metastasis of rectal cancer.

Background: Preoperative diagnosis of lymph node metastasis is important in determining the optimal therapy for rectal cancer. It has been shown that diffusion-weighted magnetic resonance imaging (DWI) is a useful tool for detecting malignant tumors.

Methods: One hundred twenty-nine consecutive patients with rectal cancer were examined with DWI + conventional (T1-weighted and T2-weighted) MRI and computed tomography (CT). All 129 patients underwent rectal resection with total mesorectal excision. Findings on DWI + conventional MRI and CT were compared with those from histopathologic examinations.

Results: Fifty-nine (46%) patients had metastatic lymph nodes on histopathologic examinations. Two hundred twenty (18%) of 1,250 lymph nodes were pathologically positive for tumor metastasis. The overall patient-based sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of DWI + conventional MRI were 93, 81, 81, 93, and 87%, respectively. Corresponding values of CT were 73, 79, 74, 77, and 76%, respectively. The overall node-based sensitivity, specificity, PPV, NPV, and accuracy of DWI + conventional MRI were 97, 81, 52, 99, and 84%, respectively. Corresponding values of CT were 86, 80, 48, 96, and 81%, respectively.

Conclusion: DWI + conventional MRI is effective for the detection of lymph node metastasis and useful for selection of the optimal therapy for rectal cancer.