The Fukushima prefectural government is implementing the Thyroid Ultrasound Examination (TUE) program for residents aged 18 years or younger living in Fukushima Prefecture at the time of the nuclear accident. The results of the first-round survey showed that the prevalence of thyroid cysts was approximately half the total number of participants. Therefore, we analyzed the detection rate and maximum diameter of thyroid cysts in more detail, based on the results of second- and third-round surveys, to determine their characteristics. We analyzed 284,074 participants who completed Full-scale Surveys (FSSs). The second and third-round surveys were considered the 1st and 2nd FSSs, respectively. The detection rate of thyroid cysts was 57.4% in males and 61.0% in females, with the highest prevalence observed at 11 and 13 years of age, respectively. The median maximum diameter of thyroid cysts was 2.7 mm (interquartile range [IQR]: 2.1-3.3) in males and 2.8 mm (IQR: 2.2-3.6) in females, with a tendency to increase with age. Both the detection rate and maximum diameter were associated with BSA. Among participants who underwent both the 1st and 2nd FSSs, cysts appeared in 10.9% and disappeared in 6.1% at the 2nd FSS. The appearance of cysts was associated with younger age, female sex, and the presence of nodules. Disappearance of cysts was associated with older age, female sex, larger BSA, and smaller maximum cyst diameter. This study is expected to help advance the TUE program and elucidate the mechanisms underlying the formation and disappearance of thyroid cysts.
Keywords: Appearance; Children; Disappearance; Fukushima; Thyroid cyst.