How frequently is the thymus seen on whole-body iodine-131 diagnostic and post-treatment scans?

The purpose of the study was to determine how often the thymus is visualized on whole-body radioiodine scans. One hundred and seventy-five patients had 325 diagnostic scans and 200 post-treatment scans. Activity in the mediastinum possibly consistent with the thymus was seen on seven scans in six patients. Four of these were diagnostic scans (three were second followup scans, and the fourth, a third follow-up scan). Three post-treatment scans demonstrated mediastinal uptake. Only one patient had persistent mediastinal uptake on both a post-treatment scan and a subsequent follow-up diagnostic scan. None of these six patients were treated as a result of this finding and none has clinical or biochemical evidence of metastatic disease.