Endocrine Abstracts

Introduction: Tc99m-Sestamibi+I-123 subtraction using planar and SPECT-CT (SPECT-CT ^99mTc-MIBI parathyroid) is commonly used to investigate primary hyperparathyroidism (PHPT). We previously reported the sensitivity and positive predictive value of 4D CT parathyroid as the second line investigation in patients with non-diagnostic SPECT-CT ^99mTc-MIBI parathyroid (https://www.endocrine-abstracts.org/ea/0041/ea0041ep164). A common cause of indeterminate SPECT-CT ^99mTc-MIBI parathyroid is the confounding factor of multi-nodular goitre or nodules. We have continued to use this investigative modality regarding pre-operative parathyroid adenoma (PA) localisation and informed patients the chance of finding parathyroid lesion in question at surgery. Patients with positive SPECT-CT ^99mTc-MIBI parathyroid were referred without 4D CT parathyroid for surgery as appropriate.

Description of methods/design: We have retrospectively reviewed and analysed our case series of patients with surgically proven PA who had also 4D-CT parathyroid following non-diagnostic ^99mTc-MIBI parathyroid. Demographic data (age, sex, pre and postoperative calcium/PTH) were presented as descriptive statistics. Histopathology report of surgical specimens was also verified. Sensitivity and specificity of 4D-CT was calculated with surgically proven PA as the reference standard.

Results: A total of 13 patients had non-diagnostic ^99mTc-MIBI parathyroid for PHPT; 10 had positive 4D-CT parathyroid (9 confirmed PA or hyperplasia, 1 normal parathyroid tissue following surgery). 3 had normal 4D-CT parathyroid (2 confirmed PA and 1 histology showed normal parathyroid tissue). In patients with surgically proven PA, 4D-CT parathyroid performed pre-operatively demonstrated a sensitivity of 82% and a positive predictive value of 90%.

Conclusion: In our case series of patients with non-diagnostic ^99mTc-MIBI parathyroid for investigation of PHPT, 4D-CT parathyroid demonstrated a consistent diagnostic value for pre-operative evaluation. Although the number of cases is small, which may limit the power of this study, it remains the preferred second line investigation of choice with high sensitivity and predictive value that allows accurate PA localisation for parathyroid surgery. With this imaging modality, both patients and the operating surgeon can be better informed of the high likelihood of finding of PA prior to surgery.

Keywords: Hyperparathyroidism, 4D-CT parathyroid, calcium metabolism.