The use of positron emission tomography with 11C-methionine in patients with primary hyperparathyroidism

Abstract

Primary hyperparathyroidism (PHPT) is a common endocrine disorder, which is nowadays often discovered incidentally by the finding of increased serum calcium and PTH in routine blood tests [1]. PHPT is due to a single adenoma in the majority of cases (85–90 %), whereas hyperplasia of all parathyroid glands occurs in 10–15 % and carcinoma is found in less than 1 %. PHPT may occur sporadically or as a part of hereditary forms [2]. Pathological parathyroid glands are mainly located close to the thyroid gland, but ectopic localization in the mediastinum, or lateral to the carotid sheath, in the carotid bifurcation and very rarely within the thyroid or the thymus may occur in up to 20 % of cases [3]. Parathyroidectomy (PTx) is the only definitive cure of PHPT and, if performed by an experienced endocrine surgeon, is successful in up to 95 % of cases. In recent years, the minimally invasive PTx (MIP) has almost replaced the traditional full neck exploration [4]. A preoperative identification of the enlarged parathyroid lesion(s) is required to perform MIP [5]. Many imaging techniques are available for locating enlarged parathyroid glands, but Tc sestamibi scan and cervical ultrasound are the most commonly used [5]. Sestamibi is taken up both by thyroid and parathyroid tissues, but it persists longer in the latter; thus a late scan can show an uptake which is rather specific for the parathyroid gland. Planar parathyroid scintigraphy may miss small or ectopic lesions. The single photon emission computed tomography (SPECT) may be helpful for giving a more precise localization of enlarged parathyroid gland(s). The sensitivity varies in different series and may reach 90–95 % using SPECT, but may be lower using planar scintigraphy [6]. The sensitivity for small adenomas, double adenomas or hyperplasia is much lower, and in the latter case computed tomography (CT)-sestamibi SPECT image fusion is superior to CT or sestamibi SPECT alone [7]. Neck ultrasound is a widely available, safe and low-cost technique and may identify a coexisting thyroid disease. The accuracy of neck ultrasound is operator-dependent. Its sensitivity can range from 42 to 82 % with a specificity of approximately 90 % [8]. CT of the neck and mediastinum and magnetic resonance imaging (MRI) are generally used in patients with persistent or recurrent PHPT, or when ultrasound and sestamibi imaging studies are negative or contradictory [5]. The TC sensitivity ranges from 50 to 88 % [5]. MRI is time-consuming and less sensitive than TC. Invasive localization techniques such as arteriography and selective venous sampling for PTH assay in the draining thyroid veins are nowadays rarely used and could be reserved to patients with prior PTx and negative imaging studies [5]. Positron emission tomography (PET) has a spatial resolution higher than that of sestamibi scintigraphy and, alone or with simultaneous CT scan (PET/CT), could be an useful tool for the identification of enlarged parathyroid glands in patient with persistent or recurrent PHPT when the results of other imaging techniques are negative or conflicting. In patients with PHPT, the PET with F-fluorodeoxyglucose (FDG-PET) showed a diagnostic accuracy lower than that of sestamibi SPECT. On the other hand, PET with C-methionine (C-Met-PET) has a sensitivity higher than that of FDG-PET [9]. C-methionine is considered to be more specific, since C-methionine seems to concentrate specifically in the enlarged parathyroid F. Cetani (&) C. Marcocci Department of Clinical and Experimental Medicine, University of Pisa, Pisa, Italy e-mail: cetani@endoc.med.unipi.it