Long-term follow-up results of the thymic cysts diagnosed by chest magnetic resonance imaging: single center retrospective study.

BACKGROUND

Thymic cysts are the most common benign lesions of the anterior mediastinum and are often misdiagnosed as solid tumors, such as thymomas, on chest computed tomography (CT), leading to unnecessary surgeries. Chest magnetic resonance imaging (MRI) has emerged as a superior modality for distinguishing thymic cysts from solid lesions. This study aimed to investigate the long-term natural course of thymic cysts diagnosed using MRI and assess the need for surgical intervention based on follow-up CT imaging.

METHODS

We conducted a retrospective single-center study of 194 patients diagnosed with thymic cysts using chest MRI between January 2017 and April 2024. Patients were followed up with serial chest CT scans for a minimum of 3 months. Changes in cyst size were classified as unchanged, decreased, increased, or disappeared. Clinical and imaging findings were analyzed.

RESULTS

Of the 194 patients (mean age, 64.0 years; 54.1% male), the mean initial cyst size was 22.1 mm [standard deviation (SD): 14.4 mm], and the mean size at last follow-up was 21.2 mm (SD: 14.5 mm), with a mean size change of -0.7 mm (SD: 7.1 mm). Over a mean follow-up period of 1.84 years (range, 0.25-6.42 years), 83.5% of patients showed no significant change in cyst size. A decrease in size occurred in 6.7% of patients (mean reduction: -15.4 mm), while 2.6% experienced complete disappearance. An increase in size occurred in 7.2% of patients (mean increase: 8.9 mm); however, no cases exhibited radiological features suggestive of malignancy.

CONCLUSIONS

Thymic cysts diagnosed using chest MRI demonstrated a stable clinical course in most cases and were safely monitored using serial chest CT without immediate surgical intervention. Our findings support the use of MRI to reduce unnecessary surgeries, and suggest the need for further large-scale prospective studies to establish standardized follow-up protocols.