Ectopic thyroid follicles in the submucosa of the duodenum.

Ectopic microscopic thyroid follicles were encountered fortuitously in the submucosa of the duodenum in a 63-year-old man undergoing pancreaticoduodenectomy for pancreatic carcinoma. The follicles, filled with a colloid-like substance, were intermingled with Brunner's glands of the duodenum. There were no signs or symptoms of a thyroid tumour. The epithelial cells and colloid-like substance were both immunoreactive for thyroglobulin but no cells stained for calcitonin. The possibility of a metastatic origin for the follicles from an occult thyroid carcinoma was excluded by the clinical and histopathological findings. These ectopic thyroid follicles cannot be explained by developmental inclusions or metastasis and may be metaplastic in nature.