F-18-Ethylcholine-PET/Ultrasound Fusion Imaging for Detection of Occult Parathyroid Adenomas in Primary Hyperparathyroidism

Purpose: Primary hyperparathyroidism is one of the most common endocrine disorders and it is only curable by surgery. This study aimed to accurately localize parathyroid adenomas (PTAs) in patients with negative results from conventional diagnostics, consisting of MIBI SPECT/CT and ultrasound, by utilizing F-18-ethylcholine-PET/ultrasound real-time fusion imaging. Fusion ultrasound is a well-established diagnostic tool that enables precise identification and localization of target structures by superimposing MRI, CT, or PET/CT with real-time B-mode ultrasound. The goal was to detect occult PTAs and enable curative targeted parathyroidectomy. Methods: A total of 49 patients with primary hyperparathyroidism were consecutively recruited from routine clinical workflows. Given negative standard diagnostics, patients were referred for FEC-PET/CT followed by FEC-PET/ultrasound. PTAs were categorized as positive, ambiguous, or negative based on FEC-PET/ultrasound findings. A retrospective data analysis was performed, examining PTA volume (ml) based on ultrasound results, SUVmax of PTAs and locoregional lymph nodes, as well as parathyroid hormone, calcium, and phosphate levels. Maximal, minimal, median, mean values, and SDs were reported. Results: Forty-nine PTAs were identified, of which 45 were solitary, whereas 2 patients had double adenomas each. The study showed relatively high rates of ectopic PTAs (28%). No significant differences were observed in FUS-based detection rates between ectopic and orthotopic lesions. PTAs, exhibited significantly higher ( P <0.05) tracer uptake [SUVmax 4.5±2.7 (4, 1.4–11.9)] compared with lymph nodes [SUVmax 2.7±1.7 (2.5, 1.2–11.8)]. SUVmax was significantly higher in positive lesions compared with ambiguous cases ( P <0.05). No significant SUVmax difference was found for lymph nodes in ambiguous cases. FUS-based PTA volume ranged from 0.2 to 2.6 ml (mean 0.5±0.5 ml). Twenty-seven patients underwent surgery, and the diagnosis was confirmed in 90% of cases. Conclusions: This study shows that FEC-PET/ultrasound offers valuable support for preoperative localization and thus can be considered as an effective and precise method for detecting parathyroid adenomas in primary hyperparathyroidism. Because of its high time and technical demands, it is reserved for challenging cases unresolved by standard diagnostics. Future technical advances may increase its accessibility.