Endocrine Abstracts (2017) 50 OC2.5 | DOI: 10.1530/endoabs.50.OC2.5

Additional value of 4D-CT in patients with primary hyperparathyroidism and negative conventional imaging; a reason to change primary imaging modality in patients over 60?

Gonnie Alkemade1, Mildred Sifontes-Dubón1, Dhruti Bhatt1, David Smith2, Rebecca Duguid3, Jack Straiton4, Jane Dymot1, Alex Graveling1 & Prakash Abraham1

1Department of Endocrinology, Aberdeen Royal Infirmary, Aberdeen, UK; 2Department of Surgery, Aberdeen Royal Infirmary, Aberdeen, UK; 3Department of Radiation Protection, Aberdeen Royal Infirmary, Aberdeen, UK; 4Department of Clinical Radiology and Nuclear Medicine, Aberdeen Royal Infirmary, Aberdeen, UK.

Introduction: Minimally invasive surgical treatment of primary hyperparathyroidism (PHPT) requires optimal preoperative localisation imaging. Parathyroid four-dimensional CT (4D-CT) has been reported to provide greater sensitivity than MIBI-SPECT/CT in localizing parathyroid adenomas. We analysed the additional value of 4D-CT in our cohort of PHPT patients.

Materials and methods: Patients who attended our parathyroid clinic between February 2016 and April 2017, with biochemically unequivocal PHPT and meeting criteria for surgery were included. All patients underwent Ultrasound and MIBI-SPECT/CT. Patients with inconclusive imaging underwent additional 4D-CT.

Results: Fifty-two patients (77% female) with a mean age of 66.2±14.9 years were included. To date 17/23 patients with inconclusive imaging results underwent additional 4D-CT. Surgical correlation so far has been positive in 4/4 positive 4D-CTs. An intrathyroidal parathyroid adenoma was found in 1 patient with a negative 4D-CT.

Table 1 Radiological localization parathyroid adenomas
Positive29/52 (55.8%)29/52 (55.8%)13/17 (76.4%)
Negative20/52 (38.5%)22/52 (42.3%)3/17 (17.6%)
Equivocal3/52 (5.7%)1/52 (1.9%)1/17 (5.9%)
Table 2 Radiation exposure
MIBI-SPECT/CT4D-CT vs 4D-CT adjusted protocolAnnual UK Background Exposure
Calculated exposure8.5 mSv18 mSv vs 12 mSv2.7 mSv

Conclusions and discussion: We have been able to radiologically localize a parathyroid adenoma in a majority of our PHPT patients with inconclusive imaging. Surgical correlation is ongoing, but results so far are promising. 4D-CT incurs radiation exposure, particularly to the thyroid and therefore should be used cautiously, especially in younger patients. Population risk for developing any cancer is 1/1000 after 4D-CT, 1/1700 after 4D-CT adjusted protocol and 1/2400 after MIBI-SPECT/CT. Lifetime attributable risk for thyroid cancer after 4D-CT is 1/100,000 in patients >60 years vs 1/2600 in patients of 30 years. MIBI-SPECT/CT is five times more expensive than 4D-CT (£630 vs £125). Currently, first line imaging consists of Ultrasound and MIBI-SPECT/CT. 4D-CT has additional value in PHPT patients with negative conventional imaging. We suggest that 4D-CT should be considered as first line imaging in patients over 60 years presenting with PHPT. Optimising the sensitivity of parathyroid imaging should result in more patients having minimally invasive surgery.