Can we improve the specificity of Parathyroid SPECT/CT scans by better pre test selection ?

Objectives: There is a current lack of agreement among medical and surgical professional society guidelines regarding the correct criteria for operative management of primary hyperthyroidism. We have observed an increase in both the number of parathyroid surgeries and sestamibi scans used for preoperative parathyroid adenoma localization. Although the reasons for the increase are likely multifactorial, there is concern that liberal operative criteria could contribute to the increase.The improved technology of SPECT/CT allows for improved detection and localization of smaller adenomas as well as normal parathyroid glands. In the absence of clear diagnostic, pathological and imaging criteria for parathyroid adenoma diagnosis, this may lead to in accurate results causing sub optimal surgeries. The objectives of this study are to further understand the relationship between size of adenoma, perioperative lab values, and surgical outcome.

Methods: From 11/2015 - 8/2017, 281 patients underwent SPECT/CT according to institutional protocol with the presumed diagnosis of hyperparathyroidism. Studies were read and dictated by an attending radiologist. Relevant patient information as well as perioperative parathyroid hormone and calcium values were gathered retrospectively. Patients with multigland hyperplasia, MEN syndrome, or without accessible perioperative lab values were also excluded from analysis. Patients were separated into two groups based on the three dimensional volume of the adenoma with separation at 0.4 cm³. A positive surgical outcome was defined by having an intraoperative PTH drop of greater than 50%.

Results: Of the 281 with SPECT/CT done at our institution during the study period, 191 met the study criteria (primary hyperparathyroidism without multigland hyperplasia, and adequate perioperative calcium, and PTH measurements). Of the 191 studies analyzed, 131 had a positive scan of which 120 underwent surgical resection. Forty-five patients (34% of positive studies) had an adenoma larger than 0.4 cm³ of which 44 had surgery and 43 had a positive surgical outcome (97%, P<0.05). The average calcium and PTH of the large adenoma group were 11.1 and 142.3 respectively. Of the 86 patients in the smaller adenoma group, 76 had surgery with 66 positive outcomes (87%). The smaller group’s preoperative calcium and PTH were 10.7 and 101.0 respectively.

Conclusions: Higher perioperative PTH and calcium values are more likely to yield a positive SPECT-CT scan with a larger adenoma and positive surgical outcome.