Parathyroid scintigraphy with the new myocardial perfusion radiopharmaceutical 99mTc-tetrofosmin was compared with 99mTc-sestamibi scintigraphy using early and delayed imaging.
Methods: The two preparations were administered on different days to the same 16 patients suffering from primary hyperparathyroidism. Anterior view gamma camera planar imaging (10-min acquisition) was performed in the period between 5 min and 3 hr after administration of the radiopharmaceutical. For most of the patients, a pertechnetate image of the thyroid was available for eyeball comparison when reading the tetrofosmin and sestamibi images. Imaging results were compared with those from histopathological examination after surgery.
Results: On early images, all the adenomas visualized with sestamibi were equally well seen with tetrofosmin and vice versa. In 6 of 11 scintigraphically detected neck adenomas, delayed imaging improved the adenoma visualization with sestamibi. In contrast, this differential washout was never seen with tetrofosmin. Histopathological examination of excised tissue specimens after neck exploration (15 patients) or thoracotomy (one patient) revealed a parathyroid adenoma in all 16 patients. Our 12 scintigraphic findings were true-positives, while the remaining four scintigraphies were false-negatives, giving a diagnostic sensitivity of 75% with both preparations. The mediastinal adenoma was detected in a patient with a history of two unsuccessful neck explorations and one unsuccessful thoracotomy.
Conclusion: Tetrofosmin has the same success rate as sestamibi for detection of parathyroid adenomas on scintigrams acquired immediately after injection. In contrast to sestamibi, delayed imaging has no diagnostic impact. Moreover, the thyroid/ parathyroid differential washout of sestamibi failed in 5 of 11 neck adenomas here detected, indicating that delayed sestamibi washout is an unreliable diagnostic criterion. Therefore, whether sestamibi or tetrofosmin is preferred for parathyroid scintigraphy, thyroid scintigraphy seems mandatory.