Differences between 99mTc-sestamibi and 99mTc-tetrofosmin uptake in thyroid and salivary glands: comparison with 99mTc-pertechnetate in 86 subjects

Quantitative assessment of thyroid-to-background ratio improves the interobserver reliability of technetium-99m sestamibi thyroid scintigraphy for investigation of amiodarone-induced thyrotoxicosis

BACKGROUND

Amiodarone-induced thyrotoxicosis (AIT) is caused by excessive hormone synthesis and release (AIT I), a destructive thyroiditis (AIT II), or a combination of both (AIT Ind). Although no gold-standard diagnostic test is available, technetium-99m sestamibi thyroid scintigraphy (99mTc-STS) has been previously reported to be an accurate tool for differentiating subtypes with important therapeutic implications. However, the information to guide reporting of 99mTc-STS is qualitative and highly subjective. This study aims to compare the interobserver reliability of 99mTc-STS before and after the use of quantitative thyroid-to-background ratios (TBRs) displayed on a time-activity curve for differentiation of AIT subtypes.

METHODS

A retrospective audit of Nuclear Medicine Departments at Royal Melbourne Hospital (Parkville, Victoria, Australia) and Cabrini Hospital (Malvern, Victoria, Australia) identified 15 consecutive 99mTc-STS studies performed for AIT. Four nuclear medicine physicians reported the studies according to previously established criteria (series 1). Quantitative TBR and estimated 'normal' range TBR were subsequently provided before the studies were reordered and reported again (series 2). Interobserver reliability was calculated using Fleiss' κ statistic for each assessment.

RESULTS

The overall percentage of agreement (PoA) and κ statistics for use of conventional 99mTc-STS for diagnosis of AIT improved from 47 to 80% and from 0.30 to 0.67 following the use of quantitative TBR displayed on a time-activity curve with reference to a normal population. Interobserver reliability improved substantially under all diagnostic comparisons, particularly for differentiation of either AIT I (PoA 80% to 94%, κ: 0.48 to 0.84) or AIT Ind (PoA 47% to 82%, κ: -0.05 to 0.51) from other types of AIT.

CONCLUSION

Use of quantitative TBR improves the interobserver reliability of reporting 99mTc-STS for investigation of different types of AIT. There is 'almost perfect' agreement upon differentiation of AIT I from AIT II and AIT Ind, with important implications for rationalizing the use of corticosteroid therapy. Prospective identification of AIT Ind is improved from 'poor' to a 'moderate' level of agreement to facilitate rational use of combination therapy at diagnosis.

Primary hyperparathyroidism: imaging to pathology

The aim of this review is to describe the multimodal imaging (ultrasound, magnetic resonance, computed tomography, and nuclear medicine) of primary hyperparathyroidism and its correlation to the pathological findings. In the last decades, imaging science has progressed a great deal. Accurate preoperative localization of the involved glands is essential for surgical success.

Imaging of parathyroid glands

Preoperative imaging studies have an important role in facilitating successful localization of adenomas for surgeons. Their use has increased and parallels the recent growth of minimally invasive parathyroidectomy. Based on findings that scintigraphy is reported to have the highest accuracy for localization of adenomas when compared with anatomic imaging techniques, this article discusses the current role and limitations of imaging, with a focus on scintigraphy, in the evaluation of patients before surgery for hyperparathyroidism.

Discordant results in Tc-99m tetrofosmin and Tc-99m sestamibi parathyroid scintigraphies

Parathyroid scintigraphies have been used to detect pathological parathyroid glands either before as well as after the parathyroid resection surgery in patients with hyperparathyroidism. One of the most utilized techniques to perform the studies is the double-phase images with Tc-99m sestamibi, which has been shown to be very accurate in the localization of enlarged parathyroid glands. Similar to Tc-99m sestamibi, Tc-99m tetrofosmin is a radiopharmaceutical initially developed to perform myocardial perfusion study that has been used to perform parathyroid scintigraphies. Although most of the papers suggest that the overall sensitivities of both radiopharmaceuticals are similar, there are some papers questioning the accuracy of Tc-99m tetrofosmin to detect abnormal parathyroid glands. In the present article, we report a case with discordant results by both methods.

Nonequivalent Results of Tetrofosmin and Sestamibi Imaging of Parathyroid Tumors

OBJECTIVE

To report the case of a patient with a large parathyroid carcinoma missed by dual-phase technetium Tc 99m tetrofosmin (TETRO) parathyroid scanning.

METHODS

We present the clinical findings, laboratory results, imaging studies, and surgical pathology report in a man with parathyroid carcinoma and review the literature regarding the use of TETRO scintigraphy in patients with hyperparathyroidism.

RESULTS

In an 83-year-old man with hyperparathyroidism, severe hypercalcemia developed in the context of nephrolithiasis. An in-office ultrasonographic evaluation of the neck revealed a partially calcified mass (2.3 by 1.3 by 1.6 cm) at the inferoposterior border of the left thyroid lobe. Technetium Tc 99m sestamibi (MIBI) scanning was requested and reported as "negative." In fact, TETRO scanning had been substituted for MIBI scanning by the management of the nuclear medicine facility. Before neck exploration, performance of dual-phase MIBI parathyroid scintigraphy revealed radionuclide retention in the left lower neck area at 120 minutes, in the same site as the ultrasonographically visualized mass. A limited left inferior parathyroidectomy was performed, and intraoperative parathyroid hormone levels declined from 254 pg/mL to 28 pg/mL 10 minutes after near-complete resection of the mass. Pathology evaluation of the surgical specimen revealed a 2,000-mg parathyroid carcinoma.

CONCLUSION

Although both agents incorporate the same technetium Tc 99m radionuclide, TETRO and MIBI parathyroid scanning are not equivalent in the detection of parathyroid tumors with use of the dual-phase technique. We do not recommend substitution of TETRO for MIBI as a cost-control measure in the evaluation of hyperparathyroidism.