Usefulness of attenuation value on computed tomography plain scan for diagnosing enlarged mediastinal lymph nodes metastases.

Background: To evaluate the diagnostic value of computed tomography (CT) attenuation in mediastinal lymph node metastases of malignant tumors. Methods: A retrospective review was conducted of a Chinese institutional database of consecutive patients with a history of malignant tumors. Those who had enlarged, necrotic, or hypermetabolic lymph nodes detected in the mediastinum during routine CT examination or positron emission tomography (PET)/CT imaging from January 2019 to December 2021 were collected for investigation. All patients underwent endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) and were followed up for at least 6 months to diagnose lymph node metastases. One-to-one correlation was attempted between the CT images of the lymph nodes and EBUS-TBNA area of the same lymph node groups and similar size. Radiologists measured size, as well as plain CT and contrast-enhanced CT (CECT) attenuation values of mediastinal lymph nodes, and evaluated the effectiveness of these variables in diagnosing lymph node metastasis. Results: A total of 135 lymph nodes of 114 patients were included in the study. In the univariate analysis, the long-axis diameter, short-axis diameter, short-axis/long-axis ratio, and plain CT attenuation values of lymph nodes were found to be statistically significantly different between the metastatic and non-metastatic lymph nodes. The areas under receiver operator characteristic (ROC) curves (AUCs) of long-axis diameter, short-axis diameter, short-axis/long-axis ratio, and plain CT attenuation value for diagnosing metastases were 0.711, 0.788, 0.671, and 0.827, respectively. The best value of the AUC for diagnosing lymph node metastases was 0.827 [95% confidence interval (CI): 0.749-0.890] using plain CT attenuation value ≤45 Hounsfield units (HU). The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were 92.8%, 69.2%, 86.5%, and 81.8%, respectively. Similar results were obtained from the 68 cases of lung cancer. Plain CT attenuation values reached the best AUC (0.860) for diagnosing lymph node metastases. Conclusions: Plain CT attenuation of lymph nodes is an effective method for diagnosing enlarged mediastinal lymph nodes with a history of multiple malignancies or lung cancer. Plain CT could be used as an additional test where there is no PET/CT available in cases of diagnostic dilemma.