[Three cases of occult thyroid cancer with mediastinal lymph node metastasis manifesting as a mediastinal cyst].

We experienced three cases (one 38-year-old male, 58-year-old and 67-year-old females) whose resected mediastinal cysts proved to be metastatic lymph nodes from occult thyroid cancer. Primary lesions in thyroid gland were detected by echography in all three cases though they were detected in one case out of two by CT, in one out of three by 201T1 scintigraphy, in two out of three by 123I scintigraphy. After these examinations on thyroid gland, operations (one lobectomy, one hemithyroidectomy, one total thyroidectomy) were performed. Primary lesions in thyroid gland were all papillary carcinomas, and ranged 4 x 3 mm to 12 x 10 mm in size. Multiple foci were found in two cases, many intrathyroidal metastases in one case, cervical lymph node metastases in two cases. In cases of mediastinal cyst, thyroid gland should be examined by echography paying attention to the mediastinal lymph node metastasis from occult thyroid cancer. When occult thyroid cancer with mediastinal lymph node metastasis is diagnosed, total thyroidectomy followed by 131I radiation therapy is recommended as the treatment for a primary lesion, because of multiple foci in thyroid gland and intrathyroidal metastases.