Radionuclide angiography in evaluation of cold solitary thyroid nodules. Improved diagnostic accuracy using flow and washout analysis.

Radionuclide thyroid angiography was performed in 252 patients with hypofunctioning thyroid nodules to evaluate differences in vascular flow and washout patterns in benign and malignant disease. Time activity curves of Tc-99m pertechnetate flow through the cold nodules were generated using region of interest software. Retention ratios of counts in the nodule at 2 minutes after radionuclide administration versus those at peak activity were derived. Patients subsequently underwent surgical excision and histopathologic examination. One hundred forty-four of the 204 benign nodules were avascular with absent radionuclide flow through the nodule. Fifty-six benign nodules were vascular with a prolonged radionuclide washout pattern with retention ratios ranging from 0.60-0.92. Forty-six of the 48 malignant nodules displayed increased perfusion with rapid radionuclide washout with retention ratios ranging from 0.28-0.48. Four benign nodules exhibited a similar flow and washout pattern. Radionuclide thyroid angiography with vascular flow and washout analysis appears to be a useful technique to differentiate between benign and malignant thyroid nodules with a high degree of sensitivity and specificity.