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

ABSTRACT 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 (). Euthyroidism maintenance was higher in the IS group (62.2% vs. 38.9%, ). The IS group showed lower subclinical hypothyroidism (33.8% vs. 54.9%, ) and hormone replacement rates (8.5% vs. 25.3%, ). Overt hypothyroidism was lower in the IS group without statistical significance (6.1% vs. 12.3%, ). Conclusion Isthmus‐sparing lobectomy better preserves thyroid function and reduces postoperative subclinical hypothyroidism and hormone replacement needs compared to isthmus‐removing lobectomy.