Changes in serum calcium and PTH of different surgical extent (A,B) and number of parathyroid preserved in situ and autotransplantation (C,D). (A) TT + anterior laryngeal and trachea LND only; (B) TT + unilateral tracheoesophageal groove LND; (C) TT + bilateral tracheoesophageal groove LND; (D) 1–2 parathyroid preservation in situ without parathyroid autotransplantation; (E) 1–2 parathyroid preservation in situ + at least 1 parathyroid autotransplantation; (F) 3–4 parathyroid preservation in situ + at least 1 parathyroid autotransplantation. PTH, parathyroid hormone; POD, postoperative day; TT, total thyroidectomy; LND, lymph node dissection.