Sestamibi scanning and minimally invasive radioguided parathyroidectomy without intraoperative parathyroid hormone measurement

Abstract

Objective: To evaluate the results of a large series of patients undergoing minimally invasive radioguided parathyroidectomy (MIRP) in which routine use of the intraoperative parathyroid hormone assay was not used, and to investigate characteristics between patients who had positive preoperative parathyroid scans versus those with negative scans.

Summary background data: The technique of parathyroidectomy has traditionally involved bilateral exploration of the neck under general endotracheal anesthesia. Parathyroid imaging using technetium-99m sestamibi (MIBI) has evolved and can localize the adenomas in 80% to 90% of patients. The MIRP technique combines parathyroid scintigraphy with a hand-held gamma detector used intraoperatively to guide the surgeon to the adenoma in patients with positive MIBI scans. Central to this technique or other unilateral approaches is a positive MIBI scan.

Methods: One hundred seventy-three patients with primary hyperparathyroidism operated on by a single surgeon between January 1998 and July 2002 were included. One hundred twelve patients underwent the MIRP procedure and by definition had a positive preoperative parathyroid scan. The technique involved injecting 20 mCi MIBI 1 hour before the surgical procedure in patients who preoperatively had positive MIBI imaging. Patients had the choice of general or MAC anesthesia. Using an incision of less than 4 cm, the dissection to the adenoma was guided by the Navigator 11-mm probe. These 112 patients and 4 additional patients who for various reasons did not have the MIRP procedure yet had positive MIBI scans were compared to 57 patients who had clearly negative MIBI parathyroid imaging.

Results: Follow-up data were available for 108 of 112 patients who underwent MIRP. No patients had persistent hypercalcemia. The long-term success rate for the MIRP group was 98%. Fifty-two percent of the MIRP procedures were performed using MAC anesthesia. Overall, gland weight and serum PTH were related to the probability of a positive MIBI scan. Multiple logistic regression revealed that females were more likely to exhibit positive scans than were males for any fixed serum PTH level. For females, there was a significant relationship between increasing serum parathyroid hormone and a positive MIBI scan. Conversely, in males, the relationship between scan positivity and serum parathyroid hormone was weaker.

Conclusions: The MIRP technique without routine intraoperative serum parathyroid hormone measurement resulted in an excellent cure rate for primary hyperparathyroidism. As the MIRP technique as well as other techniques for unilateral cervical exploration are predicated on a positive parathyroid scan, the possible effect of gender on the sensitivity of MIBI scintigraphy for the detection of parathyroid adenomas warrants further investigation.

Figure 1. Initial and delayed sestamibi parathyroid scans demonstrating a left superior parathyroid adenoma. The use of anterior, left anterior oblique, and right anterior oblique views help to demonstrate that the adenoma lies posterior but relatively close to the thyroid gland.

Figure 2. Box-and-whisker plot depicting the distribution of the log of the weight (mg) of excised parathyroid glands in patients who were scan-positive and scan-negative. The line near the center of the box denotes the sample median, while the lower and upper box ends denote the 25th and 75th percentiles, respectively. The “whiskers” extend to observations within 1.5 times the interquartile range of the box ends. In a normal distribution the whiskers mark the middle 90% of the data.

Figure 3. Box-and-whisker plot depicting the distribution of the log of the preoperative serum PTH level in patients who were scan-positive and scan-negative. The line near the center of the box denotes the sample median, while the lower and upper box ends denote the 25th and 75th percentiles, respectively. The “whiskers” extend to observations within 1.5 times the interquartile range of the box ends. In a normal distribution the whiskers mark the middle 90% of the data.

Figure 4. Box-and-whisker plot depicting the distribution of the log of the preoperative serum calcium level in patients who were scan-positive and scan-negative. The line near the center of the box denotes the sample median, while the lower and upper box ends denote the 25th and 75th percentiles, respectively. The “whiskers” extend to observations within 1.5 times the interquartile range of the box ends. In a normal distribution the whiskers mark the middle 90% of the data.

Figure 5. Plot of the probability of a positive MIBI parathyroid scan versus the log of the preoperative serum PTH level for men and women. For females, there was a significant relationship between increasing serum PTH and scan positivity (P = .003). For males, the relationship between increasing serum PTH and scan positivity was considerably weaker (P = .28).