Aspiration cytology of 131I-induced thyroiditis. A case report

Fine needle aspiration (FNA) has become an indispensable diagnostic tool for the investigation of thyroid nodules. Although 131I may induce morphologic changes similar to those associated with external radiation, a known diagnostic pitfall, the cytology literature on the subject is very sparse. This case exemplifies the thyroid cytologic changes associated with 131I exposure.

A 50-year-old male with a remote history of 131I exposure had an indurated thyroid on routine physical examination. FNA was interpreted as positive for malignant cells, and subsequently a total thyroidectomy was performed. Review of the cytologic sample revealed follicular cells with focal, marked cytologic atypia, abundant colloid, stromal fragments, and lymphocytes. The thyroidectomy specimen consisted of an indurated and nodular gland showing architecture distortion by micronodule formation, lymphocytic infiltrates, interstitial fibrosis and follicular atrophy. Marked nuclear atypia was seen in the follicular cells.

FNA of thyroid glands exposed to 131I may show significantly large, atypical follicular cells in addition to classical changes of nodular goiter and/or chronic lymphocytic thyroiditis. Although the clinical history and the diffuse nature of the process may favor a benign process in most cases, the presence of marked atypia could lead to a malignant diagnosis. Pathologists, therefore, should exercise extreme caution in interpreting cases with 131I exposure.