Determination of remnant thyroid volume:: comparison of ultrasonography, radioactive iodine uptake and serum thyroid-stimulating hormone level

Purpose: We aimed to evaluate the accuracy of ultrasonography, radioactive iodine uptake and serum thyroid-stimulating hormone level in predicting the volume of remnant thyroid gland. Methods: Sixty-six thyroidectomy patients were divided into two groups according to their functional status, i.e. those operated upon for nontoxic multinodular goitre (group one) and those operated upon for hyperthyroidism (group two). Ultrasonography, radioactive iodine uptake and thyroid-stimulating hormone assay were performed in all patients during the first post-operative month. The two groups were subdivided according to the amount of remnant thyroid volume detected on ultrasonography: < 2 ml, 2-5 ml and > 5 ml. Results: The remnant thyroid volume was positively correlated with the radioactive iodine uptake (r(s) = 0.684, p = 0.0001). The increase in remnant thyroid tissue radioactive iodine uptake was significantly greater in the patients operated upon for hyperthyroidism compared with those operated upon for nontoxic multinodular goitre (p = 0.0001). There was a negative correlation between remnant thyroid volume and post-operative serum thyroid-stimulating hormone level (r(s) = -0.865, p = 0.0001) and between remnant thyroid tissue radioactive iodine uptake and post-operative serum thyroid-stimulating hormone level (r(s) = -0.682, p = 0.0001). Conclusion: Ultrasonography is a more accurate measure of remnant thyroid volume than radioactive iodine uptake in patients operated upon for hyperthyroidism, compared with those operated upon for nontoxic multinodular goitre.