[Dermoid cyst of the ovary. False positive diagnosis in iodine 131 scintigraphy of differentiated thyroid cancers].

BACKGROUND

Total body 131-iodine labeled scintiscan is used to screen for residual tumoral tissue after ablation of differentiated thyroid carcinoma. At therapeutic doses, radioactive iodine can also be used for treatment. Thyroglobulin level, usually undetectable a few months after total thyroidectomy and metabolic irradiation with 131-iodine in patients without initial metastases, is absolutely necessary for interpreting the scintiscans. Iodine uptake occur in dermoid cysts which usually contain thyroid tissue.

CASE REPORT

A 44-year old woman underwent total thyroidectomy with node dissection for papillary carcinoma of the thyroid with a vesicular architecture. Four months later, the total body 131-iodine scintiscan demonstrated a round zone of uptake in the pelvic area. The lesion was found to be a typical dermoid cyst. No thyroid or tumoral tissue could be demonstrated.

DISCUSSION

Dermoid cysts can be the cause of false positive 131-scintiscans in patients followed after resection of differentiated thyroid carcinoma. Unlike previously reported cases, the dermoid cyst in this patient was totally devoid of thyroid tissue.