In vivo characterisation of parathyroid lesions by use of gamma probe: comparison with ex vivo count method and frozen section results.

OBJECTIVE

In this study we hypothesized that if timing of gamma probe-guided parathyroidectomy were individualized according to an optimal-time-to-surgery technique, in vivo characterization of parathyroid lesions would be possible. We compared our findings with an ex vivo counting method ("20% rule") and frozen section results.

STUDY DESIGN AND SETTINGS: Thirty-five patients who were referred for surgical treatment of hyperparathyroidism were studied. Maximum parathyroid to thyroid sestamibi uptake ratio (UR(max)) was measured by use of preoperative dynamic scintigraphy. The interval between sestamibi injection and UR(max) was defined as the optimal time to surgery. On the day of surgery, the patients received the same dose of sestamibi and were taken to the operating room at UR(max) as determined by preoperative scintigraphy. Intraoperative in vivo gamma probe counts from parathyroid lesions were compared with in vivo contralateral background thyroid counts (in vivo/Bkg) and to ex vivo parathyroid counts relative to postexcision background of the adjacent normal tissue (ex vivo/Bkg).

RESULTS

A total of 70 excised lesions were evaluated. In vivo/Bkg counts obtained from parathyroid adenoma were significantly different from parathyroid hyperplasia (z = -3.093, P = 0.002) and other lesions (z = -3.958, P = 0.0001). By receiver operating characteristic curve (ROC) analysis, we found the cutoff value for the in vivo/Bkg counts ratio to be 103% to differentiate parathyroid adenoma from hyperplasia with a sensitivity, specificity, and accuracy of 82.5, 65, and 74.4%, respectively. On the other hand, sensitivity, specificity, and accuracy of the ex vivo/Bkg method to differentiate parathyroid adenoma from hyperplasia with a cutoff value of 34.7 was found to be 70.8%, 60%, and 65.9%, respectively. The difference between the accuracy of these 2 tests was not significant statistically (P = 0.137). Sensitivity of frozen section to differentiate parathyroid adenoma and hyperplasia was 76.2% and 33.3%, respectively.

CONCLUSIONS

Patient-specific optimal protocol for timing of sestamibi injection together with in vivo/Bkg method is a useful alternative method in guiding the surgeon to differentiate parathyroid adenoma from parathyroid hyperplasia and other tissues and may help surgeons' decisions during the operation. Combined use of in vivo/Bkg and ex vivo/Bkg methods may give more accurate results than frozen section.