Multiple surgeries to resect or remove parathyroid glands are necessary for up to 7 percent of patients with hyperparathyroidism, a syndrome of glandular hyperactivity resulting in an overproduction of parathyroid hormone (PTH) and increased levels of calcium. Planar scintigraphy with I-123 and Tc-99m sestamibi may be the most accurate imaging method for reoperative localization of the parathyroid glands, according to a study published in the May issue of The Journal of Nuclear Medicine .
A majority of surgeries for hyperparathyroidism are effective, but anywhere from 2 to 7 percent of patients need additional operations due to persistent or recurrent glandular dysfunction. After initial surgery, reoperation is associated with scarring and skewing of the parathyroid glands, ectopic localization, and a higher incidence of complications. The conventional method of surgical mapping is selective venous sampling (SVS), an invasive procedure requiring catheterization through the femoral vein and blood analysis. Localization of the parathyroid glands with molecular imaging is well established, but there is a range of imaging techniques available.
Camilla Schalin-Jantti, MD, PhD, from the division of endocrinology, department of medicine, University of Helsinki, Finland, and colleagues, reviewed four different operative mapping methods for repeat hyperparathyroid surgeries. Planar scintigraphy with I-123/Tc-99m sestamibi was shown to be the most accurate mapping technique from the study’s selection.
“To the best of our knowledge, this is the first prospective study directly comparing the performance of four localization techniques—that is, planar scintigraphy with I-123/Tc-99m sestamibi, Tc-99m sestamibi SPECT/CT, C-11 methionine PET/CT, and SVS—in the setting of complicated primary hyperparathyroidism,” wrote Schalin-Jantti et al. “The results demonstrate that I-123/Tc-99m sestamibi, which in general is widely available, performs well also in the re-operative setting, with an accuracy of 59 percent for indicating the correct side of the neck and 48 percent for a more precise localization.”
For this prospective study, 21 patients with hyperparathyroidism and one or two previous surgeries to treat their condition were recruited and underwent multiple imaging studies each with I-123/Tc-99m sestamibi, Tc-99m sestamibi SPECT/CT, C-11 methionine PET/CT and SVS. Results of preoperative localization were interpreted by five readers for imaging studies and three for SVS procedures. Subsequent surgeries were performed at Helsinki University Hospital between November 2009 and February 2012 and initial data were compared to postoperative outcomes, as well as histology and biochemical cure.
After resurgery, a total of 18 out of 21 subjects (86 percent) were biochemically cured. Of these, 19 parathyroid glands were removed from 17 patients. The remaining individual had an unclear histology report. All methods were able to localize the pathologic parathyroid gland, but planar scintigraphy with I-123/Tc-99m sestamibi revealed two separate pathologic focuses on either side of the neck of one patient that no other method indicated. In the remaining three patients with continued grandular dysfunction, preoperative planar and SPECT/CT imaging studies were negative, SVS was false predictive for all three and C-11 methionine was false predictive for one. No thyroid or no other gland tissues were resected for these patients.
Authors cited a previous study that concluded superiority of early SPECT/CT (at 20 minutes after injection) over planar scintigraphy for this application. This study was based on SPECT/CT imaging data at two hours and planar imaging with dual imaging agents.
“It is possible that performance could have been enhanced by performing imaging already at 20 min, as in the study by Lavely et al,” wrote the researchers. “However, of note, planar scintigraphy was performed using double tracers in the present study, whereas Lavely et al. used a single-tracer technique. Tc-99m sestamibi is not a parathyroid tissue–specific tracer but is also taken up by thyroid tissue. Comparison with a second tracer, taken up by the thyroid gland only, is therefore recommended.”