Solitary lung metastasis found nine years after surgery for a thyroid tumor

Thyroid follicular carcinoma and follicular adenoma are indistinguishable cytologically, thus they are grouped togeter as follicular neoplasms. The diagnosis of follicular carcinoma depends on either vascular or capsular invasion histologically. Follicular carcinoma often invades blood vessels, and hematological spreading is the usual metastatic route. We presented a 66-year-old man receiving subtotal thyroidectomy for nodular goiter, which was diagnosed as follicular adenoma pathologically. One tumor over right lower posterior lung field was noted incidentally 9 years after the operation. Computerized tomography guided lung biopsy for the tumor revealed thyroid tissue. We reviewed the previous pathological specimen of thyroid nodule and found vascular invasion, The previous diagnosis should be modified as thyroid follicular carcinoma, and the new pulmonary lesion was a distant metastasis. The patient received radioactive iodine and long-term thyroxine treatment. In this case, both the lung metastasis found 9 years after surgery for a thyroid nodule and the lung metastasis presenting as a solitary tumor are rare presentations of follicular carcinoma. For a follicular neoplasm, detailed pathological examination to detect the possible vascular or capsular invasion is important to avoid the possibility of follicular carcinoma misdiagnosed as follicular adenoma. Follicular carcinoma often recurs with distant metastasis. Metastasis of follicular carcinoma should be the first impression when a tumor is found in a patient with history of follicular carcinoma or follicular adenoma.