Endocrine Abstracts

Introduction: Tc99m-Sestamibi+I-123 subtraction using planar and SPECT-CT is commonly used to investigate PHPT. Our centre previously published sensitivity and specificity of 92 and 86% respectively for Tc99m-Sestamibi+I-123 subtraction. Five false-negative studies required neck exploratory surgery. One false-positive study incorrectly localised a PA which was not found in surgery (n=67). In recent years 4D-CT parathyroid has emerged as a useful technique to detect and localise PA in the work-up of patients with PHPT. We have been using 4D-CT as a second line investigation following an indeterminate Tc99m-Sestamibi+I-123 subtraction.

Description of methods/design: We retrospectively reviewed case records of patients with surgically proven PA who had also 4D-CT post subtraction scan. A common cause of indeterminate Tc99m-Sestamibi+I-123 subtraction is the confounding factor of multi-nodular goitre or nodules.

Demographic data (age, sex, pre and postoperative calcium/PTH) were presented as descriptive statistics. Histopathology of surgical specimens was also examined. Sensitivity and specificity of 4D-CT was calculated with surgically proven PA as the reference standard.

Results: Eight patients had indeterminate Tc99m-Sestamibi+I-123 subtraction for PHPT; seven had positive 4D-CT parathyroid (six surgical specimens confirmed PA, one normal parathyroid tissue). One had normal 4D-CT and histology confirmed normal parathyroid tissue. In patients with surgically proven PA, 4D-CT parathyroid performed pre-operatively demonstrated a sensitivity of 83% and a positive predictive value of 83%.

Conclusion: In a cohort of patients with indeterminate subtraction scans for investigation of PHPT, 4D-CT parathyroid significantly improved the diagnostic value for pre-operative localisation. It is therefore the preferred second line investigation of choice, with high sensitivity and predictive value allowing accurate pre-operative localisation for minimally invasive parathyroidectomy. The patients can also be better informed of the likelihood of finding of PA prior to surgery.