Radioiodine whole body scintigraphy is a sensitive method for detection of thyroid cancer but false-positive scan results had been reported due to ectopic thyroid tissue in the mediastinum or thyroid tissue containing teratoma. Here we report two cases of ectopic thyroid tissue mimicking metastatic thyroid cancer. Case A was a 57-year housewife complained a lump over the right neck during the annual physical check-up. A sonography of thyroid gland showed a 1 cm hypoechoic nodule in the right lobe. Robotic total thyroidectomy was performed and disclosed a 0.7 cm single papillary thyroid cancer and local lymph node invasion with T1aN1aMx, staging. The follow up serum thyroglobulin level was 0.5 ng/mL, anti-thyroglobulin antibody 1.2 IU/mL (normal < 4.1 IU/mL) and 120 millicurie radioiodine whole body scintigraphy showed a nodular lesion with high tracer accumulation in the anterior mediastinum consistent with ectopic thyroid tissue. Case B was a 42- year housewife complained a lump over the right neck for six months without tenderness or swallowing disturbance. Neck sonography showed a 4 cm hypoechoic nodule in the right thyroid lobe. A neck exploration with total thyroidectomy showed a 4-cm papillary thyroid cancer without loco-regional invasion. Postoperatively the serum thyroglobulin was still as high as 39 ng/mL and 100 millie radioiodine treatment showed increased uptake over the right pelvic area and two intense spots over the neck. The patient underwent an abdominal exploration with right ovary resection, which showed teratoma containing thyroid tissue.
In conclusion, these two cases demonstrate the occurrence of false positive radioactive scintigraphy in patients with a history of papillary carcinoma of thyroid, and highlight the need to consider ectopic thyroid tissue as well as metastatic disease.