MRI Diagnosis of Mesorectal Lymph Node Metastasis in Patients with Rectal Carcinoma. What is the Optimal Criterion

Background: Preoperative diagnosis of lymph node metastasis is often difficult. A number of different criteria have been advocated in the literature, however, an optimal criterion has not yet been determined in patients with rectal carcinoma. Patients and Methods: Fifty-one patients, undergoing radical surgery with total mesorectal excision, were examined with reference to regional lymph node status. MRI and pathological findings were compared, and an optimal preoperative criterion was clarified by receiver operating characteristic (ROC) analysis. Results: Among size, shape and internal structure criteria, size was a significant factor for diagnosing metastatic lymph node on MRI. ROC analysis showed that a criterion of 6-mm or larger in the longitudinal axis was the most reliable in differentiating metastatic and non-metastatic lymph nodes, with overall accuracy of 78%. Conclusion: A 6-mm longitudinal diameter criterion is thought to be most optimal in the evaluation of mesorectal lymph node status in patients with rectal carcinoma. Rectal carcinoma is one of the major malignancies in the gastrointestinal tract. Significant determinants of patients' survival are positive involvement of the circumferential margin and lymph node metastasis (1-4). Recently, magnetic resonance imaging (MRI) has become one of the promising diagnostic tools in rectal carcinoma patients. In the evaluation of depth of tumor invasion, the diagnostic accuracy of MRI is superior to that of CT scan and almost equal to that of endorectal ultrasound (5,6). On the other hand, preoperative diagnosis of lymph node metastasis is often difficult in spite of the recent refinements of these imaging studies. There have been a number of different criteria advocated in the literature (7-18), however, an optimal criterion has not yet been determined in patients with rectal carcinoma. Therefore, we conducted this study to explore an optimal criterion for preoperative diagnosis of lymph node metastasis in patients with rectal carcinoma by high resolution MRI.