Incidentally detected liver metastasis of well-differentiated follicular carcinoma of the thyroid, mimicking ectopic thyroid

A case of incidentally detected liver metastasis of follicular carcinoma of the thyroid, histologically mimicking ectopic thyroid, is described. The p atient was a 48-year-old woman. A 2-cm mass was incidentally detected in th e left lobe of the liver by abdominal computed tomography (CT) scan. Partia l liver resection was performed for diagnosis and treatment. Histologically , the liver nodule was composed of small-to-large follicles containing coll oid material. The lining epithelium was flat or cuboidal and showed no cell ular or nuclear atypia. Immunohistochemical studies for thyroid-specific pr oteins, thyroglobulin (Tg), triiodothyronine (T3) and thyroxine (T4), sugge sted that the nodule was of thyroid origin. Therefore, a differential diagn osis of metastasis of well-differentiated thyroid cancer, ectopic thyroid t issue and teratoma was made. The patient had a history of subtotal thyroide ctomy performed 8 years ago due to a thyroid tumor. The original surgical s pecimens of the thyroid tumor were diagnosed as follicular adenoma. Additio nal sections of the specimen were reviewed and an area of convincing vascul ar invasion was found that was suggestive of follicular carcinoma. Subseque nt whole-body examination failed to find other metastases. It was determine d that the liver tumor was metastasized from well-differentiated follicular carcinoma of the thyroid.