Endometriosis cyst of the ovary with iodine 131 uptake: first case report of false positive radioiodine uptake for differentiated thyroid carcinoma

A whole body scan is performed after a radioiodine treatment in patients wi th differentiated thyroid carcinoma. This scan is useful coupled with thyro globulin 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 car cinoma. Two years and a half after, ultrasonography of the neck showed a sm all lymph node in homolateral side of carcinoma. It was decided to begin tr eatment with iodine 131. The post-therapeutic scan showed an abnormal pelvi c uptake. IRM found no osseous abnormality but an ovarian lesion. After sur gery, histological diagnosis was an endometriosis cyst without thyroid or t umoral cells. Abdominal ou pelvic iodine false positive are rare. Ovarian c ysts may be the cause of false positive radioiodine uptake. Endometriosis c yst was not previously described and the mecanism of iodine uptake is not c lear.