Endocrine Abstracts

Introduction: The gold standard for evaluating Occult Parathyroid Adenomas (OPa) in patients with biochemical pattern of primary hyperparathyroidism (PHPT) is the 99mTc-MIBI parathyroid scan. 18F-Fluorocholine (18F-FCH) PET/CT has been proposed as a potential technique for detection and localization of OPa when 99mTc-MIBI scan is negative or inconclusive.

Aims: To evaluate sensitivity and positive predictive value of 18F-Fluorocholine PET/CT in patients with biochemical PHPT with negative or inconclusive 99mTc-MIBI scan. To correlate 18F-FCH PET/CT findings with clinical and surgical characteristics.

Methods: We analyzed all subjects with biochemical PHPT attended in our department (January–December 2018) with a negative/inconclusive 99mTc-MIBI in which 18F-FCH PET/CT was performed. Patient characteristics, time of diagnosis of PHPT, serum calcium and parathyroid hormone (PTH) levels were recorded. In those patients who underwent parathyroidectomy, affected glands, type of surgery, postoperative serum calcium, PTH levels and pathological features were correlated with 18F-FCH PET/CT findings. Differences were considered significant for ap value <0.05. SPSS Statistics package was used for statistical analysis (Mann-Whitney, Chi-square and T student tests).

Results: A total of 23 subjects with biochemical PHPT with negative (n=19) or inconclusive (n=4) 99mTc-MIBI scan were included (74.47% female, 61.4±14.7 years, time since diagnosis 24.7±30 months, 17.4% with previous unsuccessful surgery, calcium 2.69±0.18 mmol/l, PTH 21.75±28 pmol/l, 3 subjects with MEN1 and 1 with familiar PHPT). 18F-FCH PET/CT was positive in 18 patients, negative in 4 and inconclusive in 1. No differences were found between subjects with positive and negative 18F-FCH PET/CT in the analyzed variables (a tendency to higher PTH was observed in subjects with positive 18F-FCH PET/CT (P=0.057)). Parathyroidectomy was performed in 12 patients (11 patients are pending of surgery), resulting in 10 cases a solitary OPa by pathology. OPa were located 6 in the left upper gland, 2 in the left lower gland and 2 in the right lower gland. 18F-FCH PET/CT localization was concordant with the excised OPa in all patients except for one case. In one case of failed surgery PET indicated an ectopic gland and in the other case a left low gland. Moreover, elevated preoperative PTH and serum calcium decreased 10 minutes after surgery.

Conclusions: In our series of patients with biochemical PHPT and negative/inconclusive 99mTc-MIBI parathyroid scan, 18F-FCH PET/CT offers greater sensitivity and precision during performance of parathyroidectomy (sensitivity 78.2%, positive predictive value 83.3%). No clinical or biochemical data was associated with PET positivity.