Radiation-associated thyroid tumors: extent of operation and pathology technique influence the apparent incidence of carcinoma.

Abstract

A prospective study and follow-up program of 2,118 patients with prior low-dose head and neck irradiation, entered into a thyroid screening project, allowed us to examine how the extent of operation and pathology technique influenced the incidence of thyroid carcinoma. Patients with palpable nodular thyroid disease were referred to their physicians with a recommendation for surgery: 107 patients had thyroid surgery in community hospitals (CHs) where enucleation of the nodule or lobectomy was the usual operation, and 29 patients had surgery at Milwaukee County Medical Complex (MCMC) where near-total thyroidectomy was routine. Lymph nodes were sampled in 69% of MCMC operations but in only 16% of CH operations. The pathologist's usual method at MCMC was to submit the total surgical specimen and to do serial sections. Less than total specimen examination and random sections typically were done in community hospitals. The mean age and sex ratio of the patients and size of thyroid lesions in the two groups were not different. Cancer was found in 59% (17/29) of patients who underwent operation at MCMC, while only 21% (22/107) of patients who underwent operation in CHs were found to have carcinoma (P less than 0.001). Surprisingly, there was nearly uniform agreement (99%) in the diagnoses made by MCMC and CH pathologists, and the incidence of microscopic foci of carcinoma was similar in both groups. We conclude that the incidence of thyroid carcinoma found in patients with prior head and neck irradiation who have had operation for thyroid nodules is related to the extent of thyroidectomy, routine lymph node sampling, the amount of resected thyroid tissue processed for histologic examination, and the absolute number of sections examined by the pathologist.