[Occult papillary carcinoma of the thyroid presenting as a solitary pulmonary metastasis].

This is a report of a quite rare case of occult papillary carcinoma of the thyroid in which the initial clinical manifestation was a solitary lung metastasis. A 58-year-old woman was referred to the Fukuoka University Hospital because a coin lesion approximately 5 cm in diameter was detected in the right lower lobe of the lung by routine roentgenographic examination. This abnormal finding by chest X-ray had been pointed out about fifteen years before. Although she did not remember the exact size of the lung tumor, it had grown minimally since that time. Otherwise, she had been in good health all her life. No abnormalities in clinical and laboratory tests were found on admission. The tumor was clinically suspected to be of benign nature (probably sclerosing hemangioma), and pulmonary lobectomy was performed. Microscopic examination of the tumor revealed a papillary carcinoma with focal areas of follicle formation and colloid production, consistent with metastatic thyroid carcinoma. Immunoperoxidase stain for thyroglobulin was strongly positive in the tumor, and this finding confirmed the thyroid origin. Repeated physical examination of the thyroid gland, thyroid scan, and thyroid function tests were all unremarkable, however, she was closely followed up for two years. Then, a thyroid nodule with cystic change was detected on the ultrasonogram. The patient underwent a right hemithyroidectomy, disclosing papillary adenocarcinoma histologically. This case suggests that thyroid cancer should be considered as possible primary site in cases of long-standing coin lesion on chest X-rays in patients without remarkable complaints and in whom the primary site is unknown. A search of the literature has revealed only five cases with occult thyroid carcinoma associated with solitary pulmonary metastasis.