Radiologic evaluation of the subcarinal lymph nodes: a comparative study

Department of Radiology, University of Michigan Medical Center, Ann Arbor 48109.

Subcarinal lymph nodes are commonly involved by metastases from cancers of both the right and left lungs. No data exist on the relative accuracy of radiologic methods for evaluating subcarinal nodes. We prospectively studied lung cancer patients who were surgical candidates with CT, MR imaging (0.35 T), esophagography, and anteroposterior tomography. Forty-six patients who subsequently underwent thoracotomy had excision or sampling of subcarinal nodes at mediastinoscopy. All 46 had CT scans, 27 had MR imaging, 23 had esophagography, and 21 had anteroposterior tomography. Receiver-operating characteristic curves were constructed for each technique, and the area under each curve was calculated. MR and CT were nearly identical in subcarinal evaluation, with areas under the receiver-operating characteristic curves of 0.90 and 0.86, respectively; both were superior to esophagography (0.55) and anteroposterior tomography (0.61). The size threshold at which subcarinal nodes were considered abnormally enlarged in this lung cancer population was 11 mm in short axis for CT, agreeing with the size threshold previously reported for a normal population. The size threshold for abnormal nodal enlargement with MR imaging was 18 mm in short axis. We conclude that CT and MR imaging are comparable in the detection of subcarinal lymphadenopathy and are superior to both tomography and esophagography. Different size thresholds for metastatic subcarinal nodes are needed for CT and MR imaging to be comparable in overall performance.
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