FCH-PET/CT in Primary Hyperparathyroidism With Discordant/Negative MIBI Scintigraphy and Ultrasonography

How has the diagnostic approach to parathyroid localization techniques evolved in the past decade? Insights from a single-center experience

The standardization of preoperative imaging in primary hyperparathyroidism is one of the current challenges of endocrine surgery. A correct localization of the hypersecretory gland by neck ultrasound and 99mTc-sestamibi (MIBI) scintigraphy are not sufficiently sensitive in some cases. In recent years, CT-4D, 18F-Fluorocholine PET/CT, and radio-guided parathyroidectomy have come into common use. The aim of this study is to evaluate the performance of 18F-Fluorocholine PET/CT after prior negative or discordant first-line imaging in patients with primary hyperparathyroidism undergoing parathyroid surgery. Monocentric observational study on patients affected by pHPT undergoing surgery from July 2009 to April 2024 at the Division of General Surgery, Cattinara Teaching Hospital of Trieste. Preoperative, intra-operative, and follow-up data were collected. The imaging methods used were neck ultrasound, 99mTc-sestamibi (MIBI) scintigraphy, and 18F-Fluorocholine PET/CT (since 2018). 172 patients were included. As first radiologic examination, neck ultrasound (US) was performed in 140 cases and 99mTc-sestamibi (MIBI) scintigraphy in 162. Ultrasound and/or scintigraphy imaging were sufficient for the identification of the gland in 127 patients (73.8%), while in 45 patients (26.2%), the localization was defined with other techniques. Particularly, three patients with negative or discordant first-line imaging underwent neck 4D-CT scan who was useful for parathyroid localization all cases (100%). Only one patient received a neck magnetic resonance (MRI) and resulted positive for preoperative localization. Starting in 2018, 29 out of 45 patients underwent 18F-FCH PET/CT yielding a positive result in 29 patients (100%). In other 16 cases (before the introduction of PET/CT in our preoperative imaging study), the preoperative localization was inconclusive and bilateral neck exploration (BNE) was necessary. The sample was homogeneous in terms of age, anthropometric characteristics, and preoperative biochemical parameters. Male/female ratio was 1:5.1. In the intra-operative site, in the cases of exclusive PET/CT positivity, in 28 cases (96.5%), a diagnostic agreement was confirmed, and the gland was macroscopically smaller or normal in size. The combination of ultrasound and MIBI scintigraphy remains the preferred imaging approach for preoperative studies of pHPT. If secondary imaging is required, 18F -FCH PET/CT stands out as the most advantageous option due to its ability to provide anatomical and functional specificity. FCH PET/CT resulted an effective imaging modality with the highest sensitivity of the available imaging techniques for localizing the hyperfunctioning parathyroid gland. Therefore, this method can be recommended in patients showing negative or inconclusive results in the conventional diagnostic imaging.

Chapter 10: What parathyroid imaging is required for hyprepratahyroidism?

In over 80% of cases, primary hyperparathyroidism results from hypersecretion of PTH by a single parathyroid adenoma. Multi-glandular involvement, combining adenoma and/or hyperplasia in varying proportions, is also possible, although less frequent. When the diagnosis of hyperparathyroidism is certain and surgery is envisaged, imaging is useful for locating the hyperfunctioning gland or glands. First-line exploration is based on a parathyroid ultrasound and a nuclear medicine examination, which may be parathyroid scintigraphy, preferably double isotope I/12399m Tc-sestamibi, with planar and tomoscintigraphic acquisitions, or a PET-CT scan with 18F-choline. In the event of negative results, it is advisable to perform a choline PET scan if the initial examination was scintigraphy. In difficult situations, additional investigations using 4D parathyroid CT or parathyroid MRI, fine-needle aspiration cytology and determination of PTH in the flushing fluid are possible after multidisciplinary discussion in an expert center.

Diagnostic Performances of 18F-Fluorocholine PET/CT as First-Line Functional Imaging Method for Localization of Hyperfunctioning Parathyroid Tissue in Primary Hyperparathyroidism

RATIONALE AND OBJECTIVES

This study evaluated the diagnostic performance of 18F-fluorocholine (FCH) PET/CT as the first-line functional imaging method for preoperative localization of hyperfunctioning parathyroid glands (HPGs) in patients with primary hyperparathyroidism (PHPT).

MATERIALS AND METHODS

This retrospective single-center study included 80 consecutive patients with PHPT, referred for FCH PET/CT between January 2018 and July 2022, and who subsequently underwent surgery. The diagnostic performance of FCH PET/CT was compared to histological results for per-lesion analysis, and to postoperative resolution of biochemical PHPT for per-patient analysis.

RESULTS

18F-FCH-PET/CT revealed 95 positive foci in 77/80 patients and was negative in 3/80 patients. Postoperative resolution of HPT was obtained in 67/80 patients (84%). Per-lesion analysis showed 80 true positives, five true negatives, 11 false negatives, and eight false positives. Seven PET-positive foci could not be compared to histology. In a first per-lesion analysis, excluding these seven anomalies, sensitivity and positive predictive value (PPV) of FCH PET/CT were 88% (95% CI: 79-94) and 91% (95% CI: 87-94), respectively. In a second per-lesion analysis considering the seven anomalies as false positives (maximum bias analysis), PPV was 84% (95% CI: 80%-87%). By per-patient analysis, FCH PET/CT correctly identified and located all pathological glands in 56/80 (70%, 95% CI: 59-80) patients.

CONCLUSION

18F-Fluorocholine PET/CT appears to be an effective pre-surgical imaging method for localization of hyperfunctioning parathyroid tissue in patients with PHPT.

Osteoporosis and Normocalcemic Primary Hyperparathyroidism (Conservatively or Surgically Managed)

Asymptomatic primary hyperparathyroidism (PHPT) involves 80-90% of the parathyroid tumor-associated cases of PHPT in the modern medical era, while normocalcemic PHPT (NPHPT) has a prevalence of 0.1-11%. We aimed to analyze the bone status and mineral metabolism in NPHPT amid conservative or surgical management. In this narrative review, we searched PubMed (between January 2020 and July 2024) via different keywords. Fourteen studies from the final analysis (388 patients with NPHPT; 1188 with PHPT; and 803 controls) showed that mean serum calcium levels varied between 2.57 and 2.26 mmol/L in NPHPT. Ten studies identified a similar 24 h urinary calcium in NPHPT versus hypercalcemic PHPT (HPHPT). Except for one study, a mandatory vitamin D analysis was performed, but the 25-hydroxyvitamin D cut-offs varied. Osteoporosis (n = 6 studies; N = 172 with NPHPT) was confirmed in 41.7-100% of NPHPT subjects. In surgery candidates, this rate might be overestimated. A DXA analysis was performed in eight studies (235 subjects with NPHPT, and 455 patients with HPHPT); two studies identified a lower BMD in HPHPT < NPHPT, but the results were not homogenous. A single study analyzed the TBS and found similar results in NPHPT. The prevalence of fractures (n = 9) varied between 7.4% and 42.8% in NPHPT. Bone turnover markers (N = 262 patients, n = 8 studies) showed lower bone formation markers in NPHPT versus PHPT (n = 3). Two studies analyzed the BMD and bone turnover markers following parathyroidectomy (161 patients, including 30 patients with NPHPT; mean ages over 60 years). To conclude, given the wide spectrum of complications associated with PHPT, an early diagnosis and proper management is essential. A more extensive screening in patients with osteoporosis and kidney stones might lead to the discovery of NPHPT, a more recently described form of PHPT. While it is still unclear whether NPHPT is an early stage of HPHPT or a separate entity, recent findings show similar osteoporosis and fracture occurrence, and an improvement in bone metabolism, following parathyroidectomy. More extensive prospective studies are crucial to understand the natural course of the disease, to reach a consensus regarding parathyroidectomy indications and surgery candidates' selection, and to ensure proper personalized management for these patients. With the evolving diagnosis methods, PHPT has become a condition with a changing clinical presentation, which now requires modern evaluation and treatment approaches.

Pitfalls of DualTracer 99m-Technetium (Tc) Pertechnetate and Sestamibi Scintigraphy before Parathyroidectomy: Between Primary-Hyperparathyroidism-Associated Parathyroid Tumour and Ectopic Thyroid Tissue

Diagnosis of primary hyperparathyroidism (PHP) is based on blood assessments in terms of synchronous high calcium and PTH (parathormone), but further management, particularly parathyroid surgery that provides the disease cure in 95-99% of cases, requires an adequate localisation of the parathyroid tumour/tumours as the originating source, with ultrasound and 99m-Technetium (99m-Tc) sestamibi scintigraphy being the most widely used. We aimed to introduce an adult female case diagnosed with PHP displaying unexpected intra-operatory findings (ectopic thyroid tissue) in relation to concordant pre-operatory imaging modalities (ultrasound + dual-phase 99m-Tc pertechnetate and sestamibi scintigraphy + computed tomography) that indicated bilateral inferior parathyroid tumours. A sudden drop in PTH following the removal of the first tumour was the clue for performing an extemporaneous exam for the second mass that turned out to be non-malignant ectopic thyroid tissue. We overviewed some major aspects starting from this case in point: the potential pitfalls of pre-operatory imaging in PHP; the concordance/discordance of pre-parathyroidectomy localisation modalities; the need of using an additional intra-operatory procedure; and the clues of providing a distinction between pathological parathyroids and thyroid tissue. This was a case of adult PHP, whereas triple localisation methods were used before parathyroidectomy, showing concordant results; however, the second parathyroid adenoma was a false positive image and an ectopic thyroid tissue was confirmed. The pre-operatory index of suspicion was non-existent in this patient. Hybrid imaging modalities are most probably required if both thyroid and parathyroid anomalies are suspected, but, essentially, awareness of the potential pitfalls is mandatory from the endocrine and surgical perspectives. Current gaps in imaging knowledge to guide us in this area are expected to be solved by the significant progress in functional imaging modalities. However, the act of surgery, including the decision of a PTH assay or extemporaneous exam (as seen in our case), represents the key to a successful removal procedure. Moreover, many parathyroid surgeons may currently perform 4-gland exploration routinely, precisely to avoid the shortcomings of preoperative localisation.