Purpose: Tc-99m MIBI scintigraphy can be useful for preoperative localizati
on of parathyroid adenomas, despite its limited sensitivity. To refine inte
rpretation, the authors conducted prospective reviews of the scintigraphic
studies of patients with concomitant thyroid nodular disease and revised th
e false-negative and false-positive results.
Materials and Methods: Seventy-seven patients with primary hyperparathyroid
ism, associated with a solitary parathyroid adenoma, underwent dual-phase M
IBI scintigraphy with subsequent injection of Tc-99m pertechnetate before s
urgery. The false-negative and false-positive scintigraphic findings were i
dentified and revised.
Results: After surgery, revision of 19 false-negative scans of the total 77
studies led to the demonstration of an adenoma in seven patients. In five
of the seven studies, the adenoma had been overlooked as a result of rapid
tracer washout. Two additional small focal lesions would have also been ide
ntified if subtraction had been used for differences in contour of the MIBI
and pertechnetate images. Four studies were interpreted falsely as abnorma
l, leading to a positive predictive value of 91%; three were associated wit
h thyroid nodular disease.
Conclusions: Differential washout of MIBI from thyroid and parathyroid tiss
ue is not universal. When MIBI is washed out rapidly from parathyroid adeno
mas, subtraction of a thyroid image should be performed and differences in
contour delineated to localize the adenoma accurately. Some, but not all, t
hyroid lesions account for the false-positive findings.