An evaluation of thallium imaging for detection of carcinoma in clinically palpable solitary, nonfunctioning thyroid nodules.

OBJECTIVE: An evaluation of thallium imaging for differentiating benign from malignant lesions in clinically palpable solitary, nonfunctioning, thyroid nodules.
METHODS: Seventy-eight patients presenting with a clinically palpable solitary nonfunctioning thyroid nodule were imaged with 3 mCi thallium-201 with a pinhole acquisition at 20 minutes and 3 hours after injection. Thallium uptake was assessed as grade 1, less than the rest of the gland; grade 2, same as the rest of the gland; and grade 3, more than the rest of the gland. All patients underwent surgery and the histology was compared with the thallium scan results.
RESULTS: Of the 78 patients presenting with solitary thyroid nodule, 13 were malignant and 65 were benign. Twenty-four patients with benign disease showed no uptake of thallium at 3 hours (grade 1). Thirty-two patients with benign disease and 2 patients with malignant lesion had grade 2 uptake at 3 hours. Eleven patients with malignant disease and 9 with benign disease had grade 3 uptake at 3 hours.
CONCLUSIONS: All malignant lesions had at least grade 2 and most had grade 3 uptake at 3 hours. All lesions with grade 1 uptake at 3 hours were benign, enabling malignancy to be excluded in one-third of cases. Thallium imaging is a useful adjunct to fine-needle cytology in evaluation of solitary thyroid nodules especially when the latter is inconclusive.