Technetium 99m tetrofosmin parathyroid imaging. Results with double-phase study and SPECT in primary and secondary hyperparathyroidism

RATIONALE AND OBJECTIVES: The aim of our study was to evaluate the sensitivity, specificity, and positive predictive value (PPV) of technetium 99m (99mTc) tetrofosmin double-phase scintigraphy and single-photon emission computer tomography (SPECT) in preoperative localization of parathyroid adenoma in case of primary and secondary hyperparathyroidism (HPT).

METHODS: Sixty-eight consecutive patients biochemically or sonographically suspected of parathyroid adenoma were included in our study. Apart from biochemical analysis of serum calcium, phosphate, and intact parathyroid hormone, double-phase scintigraphy was performed in each patient 5 and 45 minutes after injection of 370 MBq 99mTc tetrofosmin, followed by SPECT imaging. In consciousness of the scintigraphic results, ultrasound of the neck was performed as well to exclude false-positive results due to thyroid adenomas.

RESULTS: Depending on the results of the biochemical analysis in combination with the results of the scintigraphic and ultrasound examination, the patients were classified retrospectively into three groups: group A with primary HPT (n = 35), group B with secondary HPT (n = 13), and group C without any biochemical suspicion of primary or secondary HPT (n = 20). In group A, double-phase study localized 25 of 36 (69.2%) parathyroid adenomas (one double adenoma) as against 34 of 36 (94.4%) with SPECT. Nine adenomas could be visualized only by SPECT. The reason for nonvisualization on planar scans was suspected to be an ectopic location in 2 cases (retrotracheal dislocation, retrovascular dislocation), a maximal diameter less than 15 mm (9-13 mm) in 6 cases, and oxyphilic-cell-poor cellularity in 1 case. Four false-positive retention (3 thyroid adenomas and 1 papillary thyroid carcinoma) were observed. SPECT showed a sensitivity of 94.4%, a specificity of 85%, and a PPV of 91.9% in biochemically suspected primary HPT. In group B, planar scintigraphy demonstrated 12 hyperplastic glands in 5 of 13 patients, and SPECT demonstrated 20 hyperplastic parathyroid glands in 8 out of 13 patients, which corresponds to a sensitivity of 38% and 61.5%, respectively.

CONCLUSIONS: Technetium 99m tetrofosmin seems to be a promising alternative tracer with similar capabilities to 99mTc sestamibi in localization of parathyroid adenoma. SPECT showed clear advantages in terms of sensitivity over planar scintigraphy and should be used at least in cases with poor or no uptake in double-phase study. In endemic goiter areas, ultrasound of the neck should be performed to exclude false positive retention in thyroid adenomas. Technetium 99m tetrofosmin, like 99mTc sestamibi, is not ideal for localization of hyperplastic glands in secondary hyperparathyroidism because of low sensitivity.