Leiomyoma of the thyroid gland.

Primary smooth muscle tumors of the thyroid gland are very rare neoplasms, leiomyosarcomas comprising the majority of these. Only three cases of primary leiomyoma have been reported to date, all of which have occurred in females of varying ages. We present the morphological, immunohistochemical and ultrastructural features of a fourth case of leiomyoma of the thyroid gland, occurring in a post-menopausal woman with a history of uterine leiomyomas.