False-positive 131I uptake by the temporomandibular joint effusion.

A 59-year-old man with papillary thyroid carcinoma underwent total thyroidectomy and received 2 separate 100-mCi doses of 131I about 5 months apart. A whole-body scan 4 days after the second dose revealed a focal uptake in the left temporomandibular joint (TMJ). The subsequent MRI examination demonstrated that the site of elevated iodine activity was caused by a TMJ effusion.