[Ovarian endometriosis cyst with iodine 131 uptake : first case of false positive in the follow up for differentiated thyroid carcinoma].

A whole body scan is performed after a radioiodine treatment in patients with differentiated thyroid carcinoma. This scan is useful coupled with thyroglobulin level for the patient's management. When unusual uptake is found, investigations have to be done to eliminate thyroid metastasis. A 28-year old woman underwent a total thyroidectomy for micro papillary carcinoma. Two years and a half after, ultrasonography of the neck showed a small lymph node in homolateral side of carcinoma. It was decided to begin treatment with iodine 131. The post-therapeutic scan showed an abnormal pelvic uptake. IRM found no osseous abnormality but an ovarian lesion. After surgery, histological diagnosis was an endometriosis cyst without thyroid or tumoral cells. Abdominal ou pelvic iodine false positive are rare. Ovarian cysts may be the cause of false positive radioiodine uptake. Endometriosis cyst was not previously described and the mecanism of iodine uptake is not clear.