A total of 96 patients were enrolled in this study. Twelve patients were lost during follow-up or withdrew from the study before completion; accordingly, 84 patients were included. The median age of the participants was 14.27 years. By comparing the basic information of the two groups (BT and UT), no statistically significant difference was observed between them in terms of sex, age, parental marital status, only-child status, tumor size, and number of central lymph node metastases (Table 1).

The THYCA-Qol results (Additional file 1: Online Resource 1) were compared between the two groups. The THYCA-Qol assessment consists of seven symptom domains (neuromuscular, voice, concentration, sympathetic, throat/mouth, psychological, and sensory) and five single items (scar, chilly, tingling, weight gain, headache, and decreased libido), with lower scores associated with better quality of life [12]. The entry for decreased libido was deleted because the participants were children and adolescents. In terms of neuromuscular symptoms (Fig. 1a), the UT group had significantly lower scores than the BT group at 1 (P = 0.02) and 3 months (P = 0.03) postoperatively, whereas there were no statistically significant differences at 6 and 12 months postoperatively. In terms of throat/mouth symptoms (Fig. 1b), the UT group had significantly lower scores than those of the BT group at 1 (P = 0.02), 3 (P = 0.01), and 6 months (P = 0.04) postoperatively, whereas there was no statistically significant difference at 12 months postoperatively. In terms of psychological symptoms (Fig. 1c), the UT group had significantly lower scores than those of the BT group at 1 (P = 0.01), 3 (P = 0.04), 6 (P < 0.00), and 12 months (P = 0.02) postoperatively. No statistically significant differences were observed between the scores of the two groups on each entry.

THYCA-Qol results in the UT and BT groups. a Score results for neuromuscular symptoms in both groups. b Score results for throat/mouth symptoms in both groups. c Score results for psychological symptoms in both groups. THYCA-Qol: Thyroid Cancer-Specific Quality of Life Questionnaire, BT bilateral thyroidectomy, UT unilateral thyroidectomy. *P < 0.05, **P < 0.01, ***P < 0.001

The results of the PedsQL (Online Resource 2) were compared between the two groups. The scale was categorized based on four dimensions: physiological function, emotional function, social function, and academic performance; the higher the score, the better the quality of survival [13]. Regarding physiological function (Fig. 2a), the UT group scored significantly higher than the BT group 1 month after surgery (P = 0.04), while there were no statistically significant differences in the scores at 3, 6, and 12 months after surgery. Regarding emotional function (Fig. 2b), the UT group had significantly higher scores than the BT group at 1 (P < 0.00), 3 (P < 0.00), and 6 months (P = 0.01) postoperatively, while the difference was not statistically significant at 12 months postoperatively. In terms of the total scale scores (Fig. 2c), the UT group had significantly higher scores than the BT group at 1 (P < 0.00) and 3 months (P = 0.01) postoperatively, but there were no statistically significant differences at 6 and 12 months postoperatively. No statistically significant differences were seen between the two groups regarding social function scores at any time point.

PedsQL results in the UT and BT groups. a Score results for physiological function in the two groups. b Score results for emotional function in the two groups. c Scale total score for the two groups. PedsQL Pediatric Quality of Life Inventory, BT bilateral thyroidectomy, UT unilateral thyroidectomy. *P < 0.05, **P < 0.01, ***P < 0.001

The results of the EORTC QLQ-C30 (Online Resource 3) were compared between the two groups of patients. The EORTC QLQ-C30 was used to measure the quality of life in patients with all cancers and consisted of five functional scales (physical, role, cognitive, emotional, and social), one global quality of life, and nine single-item scales (fatigue, nausea and vomiting, pain, dyspnea, sleep disturbance, appetite loss, constipation, diarrhea, and financial difficulties). Higher scores on the five domains of functioning and global quality of life are associated with a better functional status; additionally, in the nine individual scales, higher scores implied more severe symptoms [14]. In terms of emotional function (Fig. 3a), the UT group had significantly higher scores than the BT group at 3 (P < 0.00), 6 (P < 0.00), and 12 months (P < 0.00) postoperatively, whereas the difference was not statistically significant at the first postoperative month. Regarding the global quality of life (Fig. 3b), the UT group had significantly higher scores than the BT group at 3 (P = 0.01), 6 (P < 0.00), and 12 months (P = 0.01) postoperatively, while there was no statistically significant difference between groups at the first postoperative month. Regarding the single item of fatigue (Fig. 3c), the UT group had significantly lower scores than the BT group at 3 (P < 0.00), 6 (P < 0.00), and 12 months (P < 0.00) postoperatively, but there were no statistically significant differences at the first postoperative month. No statistically significant difference existed between the scores of the two groups for the remaining functional scales and single items.

EORTC QLQ-C30 results in the UT and BT groups. a Score results for emotional function in both groups. b Score results for global quality of life in both groups. c Score results for fatigue in both groups. EORTC QLQ-C30 European Organization for Research and Treatment of Cancer Quality of Life Questionnaire, BT bilateral thyroidectomy, UT unilateral thyroidectomy. *P < 0.05, **P < 0.01, ***P < 0.001