Optimal Interpretative Strategy for Preoperative Parathyroid Scintigraphy

Hyperparathyroidism Caused by Coexisting Parathyroid Hyperplasia and Unilateral Bifocal Parathyroid Carcinoma

ABSTRACT

The coexistence of parathyroid hyperplasia and carcinoma is uncommon. Here we report findings of 99mTc-sestamibi SPECT/CT study in a case of unilateral bifocal parathyroid carcinoma coexisting with parathyroid hyperplasia in a 49-year-old man. The images showed 4 foci of elevated activity around the thyroid. Histopathology confirmed the 2 lesions of the left side as parathyroid hyperplasia and the other 2 lesions of the right side as parathyroid carcinoma.

ACR Appropriateness Criteria® Parathyroid Adenoma

Hyperparathyroidism is defined as excessive parathyroid hormone production. The diagnosis is made through biochemical testing, in which imaging has no role. However, imaging is appropriate for preoperative parathyroid gland localization with the intent of surgical cure. Imaging is particularly useful in the setting of primary hyperparathyroidism whereby accurate localization of a single parathyroid adenoma can facilitate minimally invasive parathyroidectomy. Imaging can also be useful to localize ectopic or supernumerary parathyroid glands and detail anatomy, which may impact surgery. This document summarizes the literature and provides imaging recommendations for hyperparathyroidism including primary hyperparathyroidism, recurrent or persistent primary hyperparathyroidism after parathyroid surgery, secondary hyperparathyroidism, and tertiary hyperparathyroidism. Recommendations include ultrasound, CT neck without and with contrast, and nuclear medicine parathyroid scans. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Combined versus subtraction-only technique in parathyroid scintigraphy: effect on scan interpretation

INTRODUCTION

Parathyroidectomy is the choice of treatment for patients with primary and tertiary hyperparathyroidism. Scintigraphic, preoperative localization of hyperfunctioning parathyroid tissue depends on either a delayed washout technique, a subtraction technique, or a combination of the two. The rationale for adopting a combination approach is its presumed superior sensitivity, but there is limited evidence to support this strategy at the cost of patient inconvenience and impact on departmental workflows.

OBJECTIVE

To determine whether a combined technique detects any additional lesions during scan interpretation compared to using subtraction-only technique in patients undergoing parathyroid scintigraphy before surgery.

METHODS

A retrospective analysis was performed of parathyroid scans at Tygerberg Hospital between January 2012 and April 2018. Scans were reinterpreted by consensus by three readers, blinded to the original interpretation. A McNemar discordant pairs analysis was then performed.

RESULTS

A total of 97 participant scans were reviewed (female: 71; mean age: 50.8 years). The number of patients with primary, secondary, and tertiary hyperparathyroidism were 63, 21, and 13, respectively. A total of 192 lesions were identified in this study. While both combined and subtraction-only approaches identified hyperfunctioning parathyroid lesions, only four lesions were identified using the combined technique that were missed by the subtraction technique. This result was not statistically significant (P = 0.125).

CONCLUSION

Based on our findings, the combined parathyroid scintigraphic technique does not improve lesion detection and may be dispensed with. Doing so will enhance patient convenience and comfort and improve departmental workflows without compromising lesion detection.

Hyperparathyroidism Caused by Coexisting Parathyroid Hyperplasia and Ectopic Parathyroid Adenomas

Tc sestamibi parathyroid scan was performed in a 35-year-old man with chronic renal failure to evaluate the cause of increased serum parathyroid hormone. Both early and delayed images showed intense activity overlapping the left upper pole of the thyroid, which was proven to be nodular parathyroid hyperplasia after parathyroidectomy. However, the levels of serum parathyroid hormone remained elevated postsurgically. A repeat sestamibi study revealed abnormal activity in the left upper mediastinum, which could also be subtly seen on initial sestamibi study. A retrosternal lesion was resected, which was confirmed as an ectopic parathyroid adenoma by pathological examination.

99mTc-Sestamibi/123I Subtraction SPECT/CT in Parathyroid Scintigraphy: Is Additional Pinhole Imaging Useful?

Objectives

This retrospective study evaluated whether the use of additional anterior ^99mTc-sestamibi/¹²³I pinhole imaging improves the outcome of ^99mTc-sestamibi/¹²³I subtraction SPECT/CT in parathyroid scintigraphy (PS).

Materials and Methods

PS using simultaneous dual-isotope subtraction methods and an acquisition protocol combining SPECT/CT and planar pinhole imaging was performed for 175 patients with primary or secondary hyperparathyroidism. All patients who proceeded to surgery with complete postsurgery laboratory findings were included in this study (n = 94). SPECT/CT images alone and combined with pinhole images were evaluated.

Results

There were 111 enlarged parathyroid glands of which 104 and 108 glands were correctly visualized by SPECT/CT (seven false positives) or SPECT/CT with pinhole (three false positives), respectively. Both sensitivity and specificity were higher with combined SPECT/CT with pinhole than with SPECT/CT alone (97% versus 94% and 99% versus 98%, resp., not significant). The false-positive rate was 6% with SPECT/CT and decreased to 3% using combined SPECT/CT with pinhole.

Conclusion

^99mTc-sestamibi/¹²³I subtraction SPECT/CT is a highly sensitive and specific protocol for PS. The use of additional anterior pinhole imaging increases both sensitivity and specificity of PS, although this increase is not statistically significant.

Accuracy of Dual Phase Single-Photon Emission Computed Tomography/Computed Tomography in Primary Hyperparathyroidism: Correlation With Serum Parathyroid Hormone Levels

PURPOSE

The objectives of this study were: 1) to determine the accuracy of dual-phase (99m)Tc -methoxyisobutylisonitrile (MIBI) with single-photon emission computed tomography/computed tomography (SPECT/CT) for the preoperative localization of parathyroid adenomas in the setting of primary hyperparathyroidism; 2) to determine the accuracy of localization for ectopic glands; and 3) to assess the relationship between accuracy and serum parathyroid hormone (PTH) levels.

METHODS

Eighty-eight patients who underwent (99m)Tc-MIBI SPECT/CT imaging for primary hyperparathyroidism at our institution over a 27-month period were retrospectively assessed. The preoperative SPECT/CT results were compared to intraoperative findings (within 1 year of imaging). The relationship between serum PTH level (within 3 months) and SPECT/CT accuracy was then evaluated.

RESULTS

Accuracy indices for the retrothyroid subgroup were sensitivity 86.7%, specificity 96.4%, positive predictive value 98.1%, negative predictive value 77.1%, and accuracy 89.8%. Accuracy indices for ectopic parathyroid adenomas were sensitivity 81.5%, specificity 100%, positive predictive value 100%, negative predictive value 92.4%, and accuracy 94.3%. For the overall group, SPECT/CT demonstrated a sensitivity of 85.1% and a PPV of 98.7%. SPECT/CT correctly identified the abnormal parathyroid gland in 60% of patients with a normal serum PTH (<6.9 pmol/L), 73% between 6.9-9.9 pmol/L, 86% between 10.0-14.9 pmol/L, 100% between 15.0-19.9 pmol/L, 88% between 20.0-24.5 pmol/L, and 100% of patients with a PTH greater than 25.0 pmol/L.

CONCLUSIONS

Dual-phase (99m)Tc- MIBI with SPECT/CT is an accurate and reliable means to correctly localize both retrothyroid and ectopic parathyroid adenomas for the purpose of surgical planning. The accuracy of SPECT/CT increases with increasing serum PTH levels.