Novel Findings on SPECT-CT Tc-99 Sestamibi Imaging for Primary Hyperparathyroidism.

BACKGROUND: The addition of SPECT-CT to Tc-99 sestamibi has become a valuable tool for parathyroid localization in primary hyperparathyroidism (PHP). However, the enhanced sensitivity of this test can lead to unexpected and significant findings. We sought to identify the frequency and types of nonparathyroid detections by SPECT-CT. MATERIALS AND METHODS: With institutional approval, we reviewed all SPECT-CT studies performed for PHP between October 2012 and August 2018 for incidental nonparathyroid abnormalities. The electronic medical record was referenced to determine the type of lesion confirmed by additional evaluation. RESULTS: Among 2413 studies, 652 patients (27%) had 677 (28%) nonparathyroid findings. The most common were thyroid nodules (331/677, 49%), including 47 (6.9%) malignancies to date: 40 papillary thyroid cancers (11 microcarcinomas), five follicular thyroid cancers, one medullary carcinoma, and one noninvasive follicular thyroid neoplasm with papillary-like features. One hundred and seventy-seven patients had pulmonary nodules (26%), of whom nine were diagnosed with primary lung lesions (6 non-small-cell cancers, one small-cell cancer, one carcinoid, and one pulmonary sequestration). SPECT-CT revealed 14 patients (2.1%) with breast abnormalities, including three cancers. Nine patients (1.3%) demonstrated metastatic diseases within the lungs (4), bones (3), and mediastinum (2). One patient was diagnosed with follicular lymphoma. Two intracranial tumors were also identified, as well as dysplastic Barrett's esophagitis (1), hiatal hernia (20, 3%), and aortic aneurysm (13, 1.8%). In all, 72/677 (10.6%) PHP patients exhibited premalignant or malignant nonparathyroid SPECT-CT findings. CONCLUSIONS: In patients undergoing localization for PHP with Tc-99 sestamibi SPECT-CT, nonparathyroid findings are frequent (27%) and can lead to newly diagnosed malignant or premalignant lesions in at least 3% of patients to date.