Effects of Isthmus-Sparing Lobectomy on Thyroid Function: A Prospective, Multicenter, Comparative Study

Background: This prospective study evaluated the impact of isthmus management (isthmus-sparing vs. isthmus-removing lobectomy) on postoperative hypothyroidism risk. Methods: Between January 2022 and March 2023, 326 euthyroid patients with benign or low-risk papillary thyroid cancer were randomized into the isthmus-sparing (IS, n = 164) or isthmus-removing (IR, n = 162) group. Administration of levothyroxine was limited to patients with overt hypothyroidism or symptomatic subclinical hypothyroidism. Results: TSH levels were significantly lower in the IS group at 3, 6, 12, and 18 months ((Formula presented.)). Euthyroidism maintenance was higher in the IS group (62.2% vs. 38.9%, (Formula presented.)). The IS group showed lower subclinical hypothyroidism (33.8% vs. 54.9%, (Formula presented.)) and hormone replacement rates (8.5% vs. 25.3%, (Formula presented.)). Overt hypothyroidism was lower in the IS group without statistical significance (6.1% vs. 12.3%, (Formula presented.)). Conclusion: Isthmus-sparing lobectomy better preserves thyroid function and reduces postoperative subclinical hypothyroidism and hormone replacement needs compared to isthmus-removing lobectomy.