Comparison between Tc-99m-tetrofosmin/pertechnetate subtraction scintigraphy and Tc-99m-tetrofosmin SPECT for preoperative localization of parathyroid adenoma in an endemic goiter area

RATIONALE AND OBJECTIVES. Technetium-99m- (Tc-99m-) tetrofosmin, a cationic , lipophilic complex like Tc-99m-sestamibi, has proved to be a potential tr acer for parathyroid scintigraphy despite some differences In washout behav ior from the thyroid gland. Previous results comparing a double-phase techn ique with single-proton emission computed tomography (SPECT) or with subtra ction techniques demonstrated a high detection rate, especially when SPECT and subtraction techniques were used, whereas the double-phase protocol rev ealed only moderate results, In this study, a direct comparison was made be tween Tc-99m-tetrofosmin/pertechnetate subtraction and SPECT to elucidate t he optimal protocol for tetrofosmin parathyroid imaging. METHODS. Twenty-three patients who were biochemically suspected of parathyr oid adenoma or hyperplasia due to primary or tertiary hyperparathyroidism w ere included in our study. In all patients, serum calcium, phosphate, and i ntact parathormone levels were analyzed in a single blood sample before Tc- 99m-tetrofosmin/pertechnetate subtraction scintigraphy and SPECT, Ultrasoun d of the neck was performed in all patients to exclude false positive resul ts due to thyroid adenomas, All patients underwent parathyroidectomy with i ntraoperative revision of all parathyroid glands, and the histological resu lts were compared with preoperative findings. RESULTS. Both imaging modalities, ie, subtraction scintigraphy and SPECT, c orrectly identified 20 of 23 (87%) histologically confirmed adenomas preope ratively, The positive predictive value was calculated to be 95% and 100%, respectively, for these two methods. Subtraction scintigraphy and SPECT sho wed concordant results in 19 patients (18 positive, 1 false-negative) and d iscordant results in 4 patients (2 positive with subtraction, 2 with SPECT) , The combined use of subtraction scintigraphy and SPECT techniques reveale d a sensitivity of 95.7% (22/23) and a positive predictive value of 95%. Th e whole procedure can be performed in less than 90 minutes per patient, Whe reas subtraction scintigraphy tended to show more false-positive retentions due to thyroid adenomas, the interpretation of SPECT may be difficult in s mall adenomas with missing thyroid/parathyroid differential washout, CONCLUSIONS. Both imaging modalities, subtraction scintigraphy with pertech netate and SPECT, are highly sensitive methods for parathyroid adenoma loca lization with Tc-99m-tetrofosmin, However, our study did demonstrate that a combination of both modalities can further improve the diagnostic accuracy . Especially in an endemic goiter area, additional ultrasound may be requir ed to avoid false-positive results due to thyroid adenomas.