Benefit of 18F-fluorocholine PET imaging in parathyroid surgery

Primary hyperparathyroidism (pHPT) is a common clinical problem for which the only definitive management is surgery. Surgical management has evolved considerably during the last several decades.

Abstract We compared 18F-fluorocholine hybrid positron emission tomography/X-ray computed tomography (FCH-PET/CT) with ultrasonography (US) and scintigraphy in patients with hyperparathyroidism and discordant, or equivocal results of US and 123I/99mTc-sesta-methoxyisobutylisonitrile (sestaMIBI) dual-phase parathyroid scintigraphy. FCH-PET/CT was performed in 17 patients with primary (n = 11) lithium induced (n = 1) or secondary hyperparathyroidism (1 dialyzed, 4 renal-transplanted). The reference standard was based on results of surgical exploration and histopathological examination. The results of imaging modalities were evaluated, on site and by masked reading, on per-patient and per-lesion bases. In a first approach, equivocal images/foci were considered as negative. On a per-patient level, the sensitivity was for US 38%, for scintigraphy 69% by open and 94% by masked reading, and for FCH-PET/CT 88% by open and 94% by masked reading. On a per-lesion level, sensitivity was for US 42%, for scintigraphy 58% by open and 83% by masked reading, and for FCH-PET/CT 88% by open and 96% by masked reading. One ectopic adenoma was missed by the 3 imaging modalities. Considering equivocal images/foci as positive increased the accuracy of the open reading of scintigraphy or of FCH-PET/CT, but not of US. FCH-PET/CT was significantly superior to US in all approaches, whereas it was more sensitive than scintigraphy only for open reading considering equivocal images/foci as negative (P = 0.04). FCH uptake was more intense in adenomas than in hyperplastic parathyroid glands. Thyroid lesions were suspected in 9 patients. They may induce false-positive results as in one case of oncocytic thyroid adenoma, or false-negative results as in one case of intrathyroidal parathyroid adenoma. Thyroid cancer (4 cases) can be visualized with FCH as with 99mTc-sestaMIBI, but the intensity of uptake was moderate, similar to that of parathyroid hyperplasia. This pilot study confirmed that FCH-PET/CT is an adequate imaging tool in patients with primary or secondary hyperparathyroidism, since both adenomas and hyperplastic parathyroid glands can be detected. The sensitivity of FCH-PET/CT was better than that of US and was not inferior to that of dual-phase dual-isotope 123I/99mTc-scintigraphy. Further studies should evaluate whether FCH could replace 99mTc-sestaMIBI as the functional agent for parathyroid imaging, but US would still be useful to identify thyroid lesions.

Ectopic parathyroid glands result from aberrant migration during early stages of development and lack of successful identification may lead to lack of success in parathyroid surgery. They constitute a common etiology of persistent or recurrent hyperparathyroidism, when they are missed at initial diagnosis. Their prevalence is about 2-43% in anatomical series and up to 16% and 14% in patients with primary and secondary hyperparathyroidism, respectively. Ectopic inferior parathyroids are most frequently found in the anterior mediastinum, in association with the thymus or the thyroid gland, while the most common position for ectopic superior parathyroids is the tracheoesophageal groove and retroesophageal region. Neck ultrasound and 99mTc Sestamibi scan are first-line imaging modalities, although with low sensitivity and specificity. However, their combination with modern techniques, such as single photon emission computed tomography (SPECT) alone or in combination with CT (SPECT/CT) increases their diagnostic accuracy. Fine needle-aspiration cytology of a lesion suspicious for parathyroid tissue and measurement of parathyroid hormone (PTH) in the aspired material further assist to the successful preoperative localization of ectopic glands. Common sites for surgical investigation are the upper thyroid pole and the upper vascular thyroid stalk behind the hypopharynx and cervical esophagus for the superior parathyroids, and the carotid artery bifurcation and the thymic tongue, for the inferior parathyroids. Radioguided minimally invasive parathyroidectomy after successful localization, assisted by rapid PTH measurement postoperatively, significantly improves surgical outcomes in patients with ectopic parathyroid adenomas.