Thallium-201 scintigraphy in the evaluation of thyroid nodules. A retrospective study of 246 cases.

There is controversy at present concerning the value of Tl-201 scintigraphy in the diagnosis of malignant thyroid nodules. The usefulness of Tl-201 scintigraphy in differentiating benign from malignant nodules was evaluated retrospectively. Tl-201 scintigraphy was performed in 101 patients with malignant thyroid nodules and in 145 with benign nodules. Early and late images were examined to compare Tl-201 uptake in nodules and normal thyroid tissue. The visual method resulted in 74% of sensitivity and 58% of specificity for the detection of malignant nodules including incidental cancers. Excluding incidental cancers, 87% sensitivity and 58% specificity were achieved. Small cancers, including incidental cancers less than 1.5 cm in diameter and small number of viable tumor cells in a large tumor also gave negative Tl-201 scintigraphic results. Forty-two percent of the benign lesions gave false positive Tl-201 scintigraphic results. It is concluded that Tl-201 scintigraphy is a sensitive and useful method to use in diagnosing malignant thyroid nodules, but is not a specific method even with late scan, for the detection of malignant thyroid nodules.