SPECT/CT, planar imaging, and ultrasound in parathyroid lesion localization

Objectives Tc-99m MIBI imaging is widely used for pre-operative localization of parathyroid adenoma or hyperplasia. Different imaging protocols such as dual tracer subtraction, and dual phase Tc-99m MIBI imaging with or without SPECT are commonly used and show moderate sensitivity and specificity. Recent technological improvements and availability of hybrid imaging modalities are changing nuclear medicine procedures. In this retrospective study we compare 1-hour SPECT/CT images with dual phase planar Tc-99m MIBI images and ultrasound images (US).

Methods A retrospective analysis of 87 patients (20 male, 67 female, mean age 56 ± 14) who underwent pre-operative parathyroid imaging and parathyroidectomy was done. After injection of 740-1110 MBq of Tc-99m MIBI, pre-operative planar images of the neck and chest were obtained at 60 and 120 min, and SPECT/CT at 60 min. Planar and SPECT/CT images were independently reviewed blinded by two nuclear medicine physicians. The accuracy of imaging modalities was compared using surgical and histological findings as the reference standard.

Results There were 95 lesions in 87 patients. Sixty-six patients had solitary adenomas, 5 had multiple adenomas, 15 had hyperplasia, and one patient had papillary thyroid carcinoma. Planar images correctly localized 46 out of 95 lesions (48%). SPECT/CT images correctly localized 63 out of 95 lesions (66%). US correctly identified 50 out of 83 lesions (60%) in 75 pts. Seventeen of the parathyroid adenomas were ectopic. Planar images detected one of these (6%), SPECT/CT ten (59%), and US two (12%). Seventy-seven of the parathyroid adenomas were non-ectopic. Planar images detected 45 of these (58%), SPECT/CT detected 52 (68%), and US 48 (73%).

Conclusions For all parathyroid lesions, SPECT/CT was more accurate than planar images or US. For ectopic parathyroid lesions, the relative superiority of SPECT/CT over the other modalities was greater than for non ectopic parathyroid lesions. For ectopic parathyroid lesions, SPECT/CT was more sensitive than CT