Endocrine Abstracts

Introduction: It is established practice to localise parathyroid lesions preoperatively using ultrasound (US) and sestaMIBI (MIBI). Whilst these imaging techniques have good sensitivity/specify, there are patients in which imaging does not localise a parathyroid lesion. ¹¹C-Methionine PET (MET PET) is an imaging modality where ¹¹C-methionine, a radioactive tracer, is taken up at sites of protein/peptide synthesis and has been demonstrated to be effective in localising parathyroid lesions. We therefore investigated the clinical utility of this imaging technique at our centre.

Methods: All patients had biochemistry prior to imaging thought to be consistent with primary hyperparathyroidism. Criteria to undergo PET imaging were inability of conventional imaging to identify a parathyroid lesion, potential intrathyroidal parathyroid lesion, and three patients where mediastinal disease was suspected. Twenty patients underwent MET PET over an 18-month period.

Results: MET PET identified a parathyroid lesion in 14/20 patients. Three out of three of these were demonstrated to be mediastinal lesions, leading to a parathyroid adenoma being successfully resected by sternotomy. 11/20 demonstrated disease in the neck. Of these 3/11 parathyroid lesions were very deep in the neck adjacent to vertebrae/oesophagus and not seen with US/sestaMIBI. In 2/11 patients MET PET demonstrated intrathyroidal parathyroid lesions and patients underwent hemithyroidectomy. All parathyroid lesions were confirmed on histology (13 adenoma and one hyperplasia). Of the 6/20 who had negative imaging, one now has a diagnosis of sarcoidosis with elevated 1,25-dihydroxycholecalciferol, one underwent bilateral neck exploration and histology demonstrated parathyroid hyperplasia. The remaining four patients are still being investigated with working diagnoses of FHH in three patients.

Discussion: MET PET is a useful additional functional imaging technique when conventional imaging fails to localise a lesion, where mediastinal disease is suspected or intrathyroidal disease needs confirmation. This can particularly helpful when deciding to refer patients for major surgery.