Thyroid morphology and function after surgical treatment of thyroid diseases.

In 1992 we performed a prospective study with 300 patients after thyroid resection. Indication for the operation was a benign nodular goiter in 280 cases, Graves' disease in 11 cases and a differentiated thyroid carcinoma in 9 cases. 269 patients (89.6%) returned for a follow-up visit which contained an ultrasound of the thyroid region and a determination of the serum thyrotropin concentration. Patients with less than 10 ml had a thyroxine replacement of 100 yg daily for six months. This therapy was discontinued for the next three months and they received their follow-up nine months after the operation. All other patients with benign diseases had their follow-up without thyroxine replacement eight weeks after the operation. The mean remnant volume was 2.4 ml for selective resected lobes, 0.8 ml after near total resection and 0.2 ml after lobectomy. We found residual or recurrent nodular tissue in 7.2% of the partially resected lobes. Visualization of the recurrent nerve and ligation of the inferior thyroid artery reduced the risk of nodular tissue in the remnant thyroid tissue significantly. Only 153 patients (62%) were treated according to our postoperative treatment schedule. Thyroxine replacement therapy was given to 96 patients at the time of their follow-up. 34% of the patients without replacement therapy had signs of insufficient hormone production of the remnant thyroid tissue. However, 22% of the patients under thyroxine replacement therapy showed signs of iatrogenic subclinical hyperthyroidism. We found a significant correlation between the volume of the remnant tissue and the serum thyrotropin concentration in patients without continuous thyroxine replacement. The corresponding calculated volume for a functionally potent remnant thyroid volume was 7.3 ml. This value was significantly higher in patients with both inferior thyroid arteries ligated at 9.8 ml. An individual postoperative therapy with iodine and/or thyroxine, which results in neither a high rate of thyrotropin elevation nor an unnescessary and undesirable part of the patients with suppressed serum thyrotropin concentrations is an indispensable component of the surgical treatment of benign nodular thyroid disease in areas of endemic iodine deficiency. As a result of this study we changed our postoperative treatment schedule. Patients with less than 10 ml remnant thyroid volume will have a continuous replacement therapy with a reduced dose of 75 yg thyroxine daily.