Abstract:Objective To explore the impact of different surgical extents on the risk of contralateral occult carcinoma and lymph node metastasis in unilateral papillary thyroid carcinoma (PTC), particularly multifocal PTC. Methods Clinical and pathological data of 2 219 unilateral PTC patients admitted to Union Hospital, Tongji Medical College, HuaZhong University of Science and Technology between January 2013 and October 2023 were collected. Preoperative ultrasound did not detect contralateral nodules in any of the patients. The patients were divided into Group 1 [total thyroidectomy (TT), n=1 056]and Group 2 [partial thyroidectomy (PT), n=1 163] based on the surgical approach. According to the distribution of nodules, they were categorized into Group A (unifocal nodule, n=1 628), Group B [unilateral multifocal small nodules, i.e., sum of largest diameters (SLD) ≤ 1 cm, n=215], and Group C (unilateral multifocal large nodules, i.e., SLD > 1 cm, n=376). General data of patients in Groups A, B, and C were compared, intraoperative and postoperative outcomes of different surgical approaches were analyzed, and the incidence of contralateral occult carcinoma and lymph node metastasis in Group 1 patients with different nodule types were evaluated. Based on whether contralateral recurrence occurred, Group 2 patients were further divided into a non-recurrence group (n=1 143) and a recurrence group (n=20). Clinical and pathological factors between the two groups were compared, and independent risk factors for contralateral recurrence were identified using multivariate logistic regression analysis. Results There were significant differences among Groups A, B, and C in central lymph node metastasis rate, extrathyroidal extension rate, and coexistence of nodular goiter (P<0.05). Significant differences were also found between TT and PT in terms of operation time, intraoperative blood loss, hospital stay, and postoperative levothyroxine maintenance dose (P<0.05). Postoperative pathology revealed that patients with unilateral multifocal large nodules in Group 1 had the highest incidence of contralateral occult carcinoma (27.35%). The incidence of bilateral central lymph node metastasis with more than two metastatic nodes in patients with unilateral multifocal large nodules was 29.15% (65/223), significantly higher than that in patients with unifocal nodule (20.98%, 150/715) (χ²=6.421, P=0.011) and patients with unilateral multifocal small nodules (16.1%, 19/118) (χ²=7.075, P=0.008). Multivariate logistic regression analysis confirmed that unilateral multifocal large nodules (OR=7.434, 95%CI: 1.736-31.885, P=0.008) and extrathyroidal extension (OR= 34.880, 95%CI: 3.192-381.158, P=0.005) were independent risk factors for contralateral recurrence in unilateral PTC patients undergoing PT. Conclusion Unilateral multifocal PTC patients have a higher risk of contralateral occult carcinoma and lymph node metastasis. For patients with preoperative ultrasound indicating unilateral multifocal lesions and a larger SLD, initial TT can effectively reduce the risk of contralateral recurrence and reoperation.