Primary hyperparathyroidism (HPT) ranks as the third most common endocrine disorder, characterized by excessive secretion of parathormone (PTH), a hormone crucial for regulating calcium and phosphorus metabolism within the body. The only cure for HPT is surgically removing the hyperfunctioning parathyroid tissue, both in symptomatic and asymptomatic settings. With the advance of preoperative medical imaging techniques, a paradigm shift has taken place in the surgical approach of this condition, evolving from an inpatient bilateral cervical exploration to an outpatient minimally invasive procedure, which has proved to be superior in outcome. Due to the small size of the glands, preoperative visualisation and localisation are mandatory for the surgeon. Several imaging methods have been researched for identifying hyperfunctioning parathyroid glands, including morphological, functional and hybrid techniques, with no clear agreement on the optimal imaging approach.The preoperative localization modalities available are ultrasonography; parathyroid scintigraphy using technetium [99mTc]Tc sestamibi (MIBI), multiphase multidetector 4D computed tomography (4DCT); magnetic resonance imaging; and recently, positron-emission tomography/computed tomography (PET/CT) using 11C- and 18F-labelled radiotracers. While ultrasound and [99mTc]Tc-MIBI scintigraphy have been long used to diagnose and monitor patients with HPT, they can lead to numerous false negative results and therefore require additional examinations.Choline PET/CT is steadily replacing conventional imaging in many centres, allowing for the localization of adenomas in three quarter of patients with negative previous imaging examinations, but is still considered a relatively new method. [11C]C-Choline ([11C]CH) PET/CT is gradually gaining ground as a reliable method of localising HPT preoperatively, due to its fast uptake in hyperfunctioning parathyroid tissue, shorter acquisition time and lower radiation exposure compared to other nuclear medicine investigations and conventional methods. [11C]CH PET/CT has been suggested to be superior in diagnostic performances, compared to other imaging methods, reaching sensitivities up to 98.9%.The aim of our retrospective, single centre study is to evaluate the diagnostic performances and the inter-observer agreement of [11C]CH PET/CT for the preoperative detection of parathyroid adenomas in patients with suspected primary HPT.

Inclusion Criteria:

• Patients with biochemically proven HPT, either through elevated serum levels of PTH or normal PTH despite hypercalcemia;
• Age ≥ 18 years old;
• [11C]CH PET/CT for HPT before eventual surgery.

Exclusion Criteria:

• Pregnancy or breast-feeding.

Retrospectively select patients who performed PET in our institution from 2022 until 2024.

Patients who meet the following criteria will be included in the study.