Measurement of Iodolipids in the Thyroid Gland and Other Biological Samples

Inclusion Criteria: Patients fulfilling all of the following inclusion criteria are eligible for the study: 1. Patients with the capacity for discernment and who agree to participate in the study and sign the consent. 2. Age ≥18 years. 3. Indication for thyroid surgery due to either nontoxic single thyroid nodule (WHO disease classification 5A01.1) or nontoxic multinodular goitre (WHO disease classification 5A01.2). 4. Normal thyroid function without anti-thyroid medication. This is ascertained by at least one serum TSH value within the reference range in the three months before surgery (if multiple values are available, the latest value should be normal). If no TSH values are available, a blood draw will be performed to measure TSH. Exclusion Criteria: The presence of any one of the following exclusion criteria will lead to exclusion of the patient: 1. Women who are pregnant or breastfeeding (a urine pregnancy test will be done at Visit 2 before randomization if applicable). 2. Intention to become pregnant during the course of the study. 3. Alcohol or drug abuse within the past 6 months. 4. Inability to follow the procedures of the study, e.g. due to language problems, psychological disorders, dementia, etc. of the patient. 5. Participation in another study with investigational drug within the 30 days preceding and during the present study. 6. Use, within the last month before the scheduled surgery, of iodine-containing medications, i.e., iodine-containing anti-cough syrups or iodine-containing disinfectants. Non-iodine-containing anti-cough syrups and non-iodine-containing disinfectants are authorized. 7. Use, within the last month before the scheduled surgery, of iodine-containing radiological contrast media. Non-iodine-containing radiological contrast media are authorized. 8. Susceptibility to iodine-induced hyperthyroidism (i.e., toxic adenoma or toxic multinodular goiter, or previous episode of iodine-induced hyperthyroidism according to the medical history). 9. Serum TSH (thyroid-stimulating hormone) level below the lower limit of the reference range. 10. Graves' disease. 11. Susceptibility to iodine-induced hypothyroidism (history of thyroid surgery, Hashimoto's thyroiditis, history of subacute or destructive thyroiditis). 12. Titer of serum thyroid autoantibodies (anti-TSH receptor, anti-thyroperoxydase or antithyroglobulin) above the reference range. 13. History of sialadenitis, regardless of etiology. 14. History of allergic reactions (any grade) to radiological contrast media, iodine-containing disinfectants, anti-cough medications, or seafood; and known hypersensitivity to iodine. 15. History of allergic reactions (any grade) to the excipients of the ""IODURE DE POTASSIUM 65 AApot cpr 65 mg" drug: lactosum anhydricum, cellulosum microcristallinum, magnesii stearas. 16. Severe intolerance to lactose or galactose (patients having been recommended by their physician to adhere to a strict regime free of the offending agent). 17. Concurrent treatment with lithium. 18. Concurrent treatment with potassium-sparing diuretics. 19. Nodule diagnosed as thyroid carcinoma or suspicious for thyroid carcinoma based on the results of a fine-needle aspiration biopsy or a tru-cut biopsy (if performed during the routine patient work-up as per standard indications). 20. Patients with hyperkalemia. 21. Dermatitis herpetiformis. 22. Congenital myotonia. 23. Hypocomplementemic urticaria/vasculitis. 24. Chronic obstructive pulmonary disease 25. Asthma 26. Heart failure stage B, C or D 27. Impaired renal function (eGFR \<60 ml/min/1.73 m2) 28. Normal urinary iodine concentration on the day of surgery (determined retrospectively).