Solitary pulmonary metastasis from occult papillary thyroid carcinoma

Pulmonary metastases from thyroid carcinoma typically cause a micronodular or miliary pattern throughout both lungs. Metastasis consisting of a solitary pulmonary nodule measuring 20 mm in diameter is rare. Here we report a case of a 66-year-old woman without a history of papillary thyroid carcinoma who presented with a pulmonary nodule measuring 20 mm in diameter, found on chest computed tomography during a health checkup. The patient underwent a right lobectomy. Microscopic examination showed well-differentiated papillary adenocarcinoma. Immunohistochemical findings were consistent with a diagnosis of pulmonary metastasis from papillary thyroid carcinoma. Solitary metastasis to the lung from occult thyroid carcinoma is quite rare, but if a pulmonary nodule is encountered in a patient without a history of thyroid carcinoma, the possibility must be considered.