Small pelvic lymph node metastases: evaluation with MR imaging

The purpose of this study was to determine if lymph node asymmetry in small (< 1.0 cm) pelvic lymph nodes was a significant prognostic feature in determining metastatic disease. Two hundred and sixteen patients who presented with pelvic carcinoma underwent magnetic resonance imaging (MRI). They were correlated with pathological findings obtained at surgery. We considered the maximum diameter (MAD) of both round- or oval-shaped suspicious masses seen in the axial plane. Two different cut-off values were determined: lymph node diameter greater than 1.0 cm (criterion 1) and lymph node diameter greater than 0.5 cm with asymmetry relative to the opposite side for lymph nodes ranging from 0.5 cm to 1.0 cm (criterion 2). With criterion 1, MRI had an accuracy of 88%, a sensitivity of 65%, a specificity of 96%, a positive predictive value (PPV) of 88% and a negative predictive value (NPV) of 88% in the detection of pelvic lymph node metastasis. By considering criterion 2, MRI had an accuracy of 85%, a sensitivity of 75%, a specificity of 91%, a PPV of 71% and a NPV of 91%. Normal small asymmetric lymph nodes were present in 5.6% of cases. Normal asymmetry of pelvic lymph nodes is not uncommon. It cannot be relied on to diagnose metastatic involvement in cases of small suspicious lymph nodes.