Unusual sites of metastasis of papillary thyroid cancer: Case series and review of the literature.

Papillary thyroid cancer (PTC) is the most common malignancy of the thyroid gland. It typically spreads via lymphatic extension. The rate of regional PTC metastasis to the neck is relatively high, while metastases outside the deep cervical chain are rare. Distant metastases are found in only 1% of patients with PTC at the time of surgery; the two most common sites are the lung and bone. We report 4 cases of PTC metastasis to unusual sites: (1) the occipital skull and internal jugular vein, (2) the parapharyngeal space, (3) the sternocleidomastoid muscle, and (4) the right atrium of the heart. It has been well documented that aggressive distant metastasis is a characteristic of PTC, and it is known to be an indicator of a poor prognosis. Some of our patients' sites of metastatic disease have not been previously reported. Patients in this series exhibited aggressive histologic findings, including columnar cell and follicular variants of papillary disease. In addition, all 4 patients demonstrated "PET-avid" disease with decreased iodine avidity.