Management of incidentally detected small anterior mediastinal nodules: Which way to go?

With increasing use of CT screening for lung cancers, there is a tendency toward increased detection of asymptomatic small anterior mediastinal nodules (SAMNs). In face of high rate of non-therapeutic surgery in these patients, workup and follow-up strategy for such lesions remains to be established.This is a real-world study in patients with SAMNs (baseline diameter ≤ 3 cm) during 2013-2018. Interval growth of the nodules was reviewed. Accuracy of preoperative diagnosis was evaluated, and tumor doubling time (TDT) was calculated in resected tumors.A total of 419 patients were entered into the study, among them 91 received surgery. Eighty-four patients (92.3%) turned out to have thymic tumors, with a non-therapeutic surgery rate of only 6.6%. For 73 patients receiving both CT and MRI examinations, the sensitivity for diagnosing thymic tumors by CT alone was merely 72.1%, which was significantly improved to 97.1% (p < 0.001) when MRI was incorporated. Among 38 thymic tumor patients who had previous CT scan before surgery, significant difference in median TDT was seen between low-grade tumors and intermediate-/high-grade tumors (23.8 vs. 10.1 months, p = 0.021). Of the 328 patients not receiving surgery, 269 (82.0%) were diagnosed of having benign cysts by CT + MRI, followed by 24 (7.3%) lymph nodes, 22 (6.7%) thymic hyperplasia, and 13 (4%) thymic tumors. During follow-up (median 33 months), 319 (97.3%) lesions remained unchanged.The majority of incidentally detected SAMNs remain stable during long-term follow-up. Incorporating MRI with CT scan is helpful in differentiating benign cysts from small thymic tumors, thus avoiding non-therapeutic intervention. Follow-up is safe and warranted upon first detection when high-grade malignancies could be ruled out by careful imaging studies.