Morphological characteristics of lateral pelvic lymph nodes in rectal carcinoma

Aim Macroscopic and imaging indicators for lymph node metastasis have been documented not in lateral pelvic lymph nodes but in mesorectal lymph nodes in patients with rectal carcinoma. We conducted this study to uncover morphological characteristics of lateral pelvic lymph nodes in patients with rectal carcinoma. Materials and methods Fifty-eight patients with locally advanced rectal carcinoma who had total mesorectal excision and lateral pelvic lymph node dissection were studied. Total number of lateral pelvic lymph nodes evaluated was 462, with 538 mesorectal lymph nodes being used for comparison. Factors of lymph nodes evaluated were size (long- and short-axes diameters), shape (ovoid and irregular), and heterogeneity of internal structure. Receiver operating characteristic (ROC) curve analysis was used to compare the diagnostic accuracy of each factor. Results Lateral pelvic lymph node at non-metastatic status appeared to be longer (4.5 vs 3.5 mm) and thinner (2.2 vs 2.6 mm) than mesorectal lymph nodes. ROC curve analysis, for discriminating non-metastatic and metastatic lateral pelvic lymph nodes, revealed that a short-axis diameter appeared to be the most prominent factor with highest area under curve (0.907) and was more reliable than either long-axis diameter (0.811) or shape (0.527) other than internal structure (1.00). A short-axis diameter was an independent risk factor for metastasis by multivariate analysis with an odds ratio of 1.29 (p < 0.0001, 95% confident interval, 1.22–1.36). The most reliable cut-off value was 4 mm with 96% of sensitivity, 68% of specificity, and 82% of overall accuracy. Conclusion Lateral pelvic lymph nodes tended to be longer and thinner than mesorectal lymph nodes at non-metastatic status. A short-axis diameter of 4 mm or larger was the prominent indicator of metastasis in lateral pelvic lymph nodes.