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

Objectives: 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.

Materials and methods: 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.

Results: 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.

Conclusion: 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.