Primary leiomyoma of the thyroid gland.

Primary thyroid leiomyomas are rare, and only four cases have been reported to date. This is a report of an additional case of primary thyroid leiomyoma in a 40-year-old male who was admitted with a painless swelling in the right thyroid lobe and underwent subtotal thyroidectomy. The surgical specimen showed a well-circumscribed, greyish-white solid nodule. Histologically, the tumour was composed of spindle cells with blunt-ended nuclei that were arranged with short intersecting bundles. Immunohistochemical staining revealed reactivity with smooth muscle actin, vimentin and desmin. Histopathologic and immunohistochemical assessments produced the diagnosis of thyroid leiomyoma. Although primary thyroid leiomyoma is rare, it should be considered in the differential diagnosis of a cold thyroid nodule.