title: Effect of Thyroid Remnant Volume on the Risk of Hypothyroidism After Hemithyroidectomy: A Prospective Study.
abstract: BACKGROUND
  Hypothyroidism is a common sequel after a hemithyroidectomy. Although various risk factors leading to hypothyroidism have been reported, the effect of the contralateral lobe's volume has been understudied. This study aimed to examine the association between the preoperative contralateral lobe's volume and the risk of postoperative hypothyroidism.
  
  
  METHODS
  During a 2-year period, 150 eligible patients undergoing a hemithyroidectomy were evaluated. The volume of the contralateral nonexcised lobe was estimated preoperatively by independent assessors on ultrasonography using the following formula: width (in cm) × depth (in cm) × length (in cm) × (π/6), adjusted for the body surface area (BSA). Postoperative hypothyroidism was defined as serum thyroid-stimulating hormone (TSH) exceeding 4.78 mIU/L. Any significant characteristics in the univariate analysis were entered into the multivariate analysis to determine independent factors.
  
  
  RESULTS
  After a mean follow-up period of 53.5 ± 9.4 months, 44 patients (29.3 %) experienced postoperative hypothyroidism, and 10 of these patients required thyroxine replacement. Hypothyroidism was associated with a higher preoperative TSH level (p < 0.001), a smaller BSA-adjusted volume (p < 0.001), fewer ipsilateral nodules (p = 0.037), and the presence of thyroiditis (p = 0.050). After adjustment for thyroiditis, preoperative TSH (p < 0.001), number of ipsilateral nodules (p = 0.048), and BSA-adjusted volume (p < 0.001) were independent factors for hypothyroidism. Patients with a BSA-adjusted volume smaller than 3.2 ml had a threefold greater hypothyroidism risk than those with a BSA-adjusted volume of 3.2 ml or more (p < 0.001).
  
  
  CONCLUSIONS
  A significant inverse association between the preoperative contralateral lobe's volume and hypothyroidism risk was observed after hemithyroidectomy. Together with a higher preoperative TSH level and fewer ipsilateral nodules, a smaller BSA-adjusted volume measured by preoperative ultrasonography independently predicted hypothyroidism.
authors.affiliation: Department of Surgery, The University of Hong Kong, Hong Kong, China. blang@hku.hk.|Division of Endocrine Surgery, Department of Surgery, Queen Mary Hospital, 102 Pokfulam Road, Hong Kong SAR, China. blang@hku.hk.
authors.forename: Brian Hung-Hin
authors.identifier: http://orcid.org/0000-0002-9362-0086
authors.initials: BH
authors.lastname: Lang
authors.affiliation: Department of Family Medicine and Primary Care, The University of Hong Kong, Hong Kong, China.
authors.forename: Carlos K H
authors.identifier: http://orcid.org/0000-0002-6895-6071
authors.initials: CKH
authors.lastname: Wong
authors.affiliation: Department of Surgery, The University of Hong Kong, Hong Kong, China.
authors.forename: Kai Pun
authors.initials: KP
authors.lastname: Wong
authors.affiliation: Department of Surgery, The University of Hong Kong, Hong Kong, China.
authors.forename: Kelvin Ka-Wan
authors.initials: KK
authors.lastname: Chu
authors.affiliation: Department of Anatomical Pathology, The University of Hong Kong, Hong Kong, China.
authors.forename: Tony W H
authors.initials: TWH
authors.lastname: Shek
mesh_terms: D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007037:Hypothyroidism / Q000209:etiology*; D008297:Male; D008875:Middle Aged; D011183:Postoperative Complications; D011379:Prognosis; D011446:Prospective Studies; D012307:Risk Factors; D015996:Survival Rate; D013964:Thyroid Neoplasms / Q000473:pathology* / Q000601:surgery*; D013965:Thyroidectomy / Q000009:adverse effects*