AB008. Analysis of natural development and changes of thymic cysts on imaging

Email: yuanchen@tmu.edu.cn.

Background: Currently, the understanding of thymic cysts among thoracic surgeons remains inconsistent. This study aimed to conduct a comprehensive follow-up on patients with thymic cysts to analyze their natural progression and imaging changes, as well as identify factors influencing the advancement or regression of these cysts.

Methods: Retrospective analysis was performed on patients with unoperated thymic cysts or those who had been operated in our department from 2014 to 2023. The follow-up time of patients was required to be at least 6 months and the patients were confirmed as thymic cysts by computed tomography (CT) + magnetic resonance imaging (MRI). Baseline patient data were collected for analysis. Univariate and multivariate Cox regression analyses were performed to assess factors affecting changes in thymic cyst size. Patients were categorized into progressive and regressive groups based on doubling time to determine optimal follow-up intervals.

Results: Compared to the stable group, most individuals in the progressive group exhibited long T1 and T2 MRI signals, initial volumes exceeding 1 cm³, and initial locations adjacent to the midline or left side of the thymus gland (Figure 1). The results from univariate Cox regression analysis indicated that middle-aged [hazard ratio (HR) =0.30, 95% confidence interval (CI): 0.12–0.73, P=0.008; median =54.00 years, range, 45.00–59.00 years] and elderly (HR =0.33, 95% CI: 0.13–0.85, P=0.02; median =65.00 years, range, 60.00–79.00 years) cohorts had more favorable prognoses than younger individuals; additionally, symptomatic patients demonstrated better outcomes compared to asymptomatic ones (HR =0.44, 95% CI: 0.22–0.88, P=0.02; median =26.00, range 0.00–52.00). In multivariate Cox regression analysis, those with initial volumes greater than 1 cm³ showed improved prognosis relative to those with volumes ≤1 cm³ (HR =3.96, 95% CI: 1.34–11.66, P=0.01; median =1.40 cm³, range, 0.13–37.70 cm³), while symptomatic individuals also fared better than their asymptomatic counterparts (HR =0.28, 95% CI: 0.11–0.69, P=0.006; median =26.00, range 0.00–52.00). The median doubling time for the progressive cohort was recorded at 35.41 (10.13–120.05) months, whereas it was noted at 19.49 (1.76–59.05) months for those experiencing regression.

Conclusions: The prognosis of young patients and patients with initial volume ≤1 was worse. Patients with symptoms have a better prognosis than those without symptoms. The best follow-up time for patients with unoperated thymic cysts was 13.72 months (about 1 year).

Keywords: Thymic cyst; developmental changes; progression-free rate; doubling time case report