Diagnostic dilemmas in parathyroid scintigraphy

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.