Usefulness of semi-automatic volumetry compared to established linear measurements in predicting lymph node metastases in MSCT

Abstract

Background Volumetry of lymph nodes potentially better reflect asymmetric size alterations independently of lymph node orientation in comparison to metric parameters (e.g. long-axis diameter). Purpose To distinguish between benign and malignant lymph nodes by comparing 2D and semi-automatic 3D measurements in MSCT. Material and Methods FDG-18 PET-CT was performed in 33 patients prior to therapy for malignant melanoma at stage III/IV. One hundred and eighty-six cervico-axillary, abdominal and inguinal lymph nodes were evaluated independently by two radiologists, both manually and with the use of semi-automatic segmentation software. Long axis (LAD), short axis (SAD), maximal 3D diameter, volume and elongation were obtained. PET-CT, PET-CT follow-up and/or histology served as a combined reference standard. Statistics encompassed intra-class correlation coefficients and ROC curves. Results Compared to manual assessment, semi-automatic inter-observer variability was found to be lower, e.g. at 2.4% (95% CI 0.05–4.8) for LAD. The standard of reference revealed metastases in 90 (48%) of 186 lymph nodes. Semi-automatic prediction of lymph node metastases revealed highest areas under the ROC curves for volume (reader 1 0.77, 95%CI 0.64–0.90; reader 2 0.76, 95%CI 0.59–0.86) and SAD (reader 1 0.76, 95%CI 0.64–0.88; reader 2 0.75, 95%CI 0.62–0.89). The findings for LAD (reader 1 0.73, 95%CI 0.60–0.86; reader 2 0.71, 95%CI 0.71, 95%CI 0.57–0.85) and maximal 3D diameter (reader 1 0.70, 95%CI 0.53-0.86; reader 2 0.76, 95%CI 0.50–0.80) were found substantially lower and for elongation (reader 1 0.65, 95%CI 0.50–0.79; reader 2 0.66, 95%CI 0.52–0.81) significantly lower (p < 0.05). Conclusion Semi-automatic analysis of lymph nodes in malignant melanoma is supported by high segmentation quality and reproducibility. As compared to established SAD, semi-automatic lymph node volumetry does not have an additive role for categorizing lymph nodes as normal or metastatic in malignant melanoma.