To determine the prevalence of thyroid malignancy in the first UK case series of patients with incidentally detected thyroid lesions on 18F-fluorodeoxyglucose positron emission tomography imaging.

A total of 235 patients were evaluated with 18F-fluorodeoxyglucose positron emission tomography imaging. Incidental focal uptake in the thyroid gland was identified in nine patients (3.8 per cent). A retrospective review of their case notes was conducted.

The rate of malignancy was 55 per cent. The mean and standard deviation of the maximum standardised uptake value was 13.1 ± 7.3 in those patients with malignancy and a nodule identified as positive on positron emission tomography. This value was 2.8 ± 1.2 in those patients without malignancy but with a nodule identified as positive on positron emission tomography (p = 0.01). A palpable thyroid nodule was more likely in those with malignant lesions (p = 0.14).

The prevalence of incidental thyroid lesions found on 18F-fluorodeoxyglucose positron emission tomography in patients with other primary malignancies is low, but the incidence of malignancy in these patients is high. Patients with a palpable thyroid nodule, focal uptake on 18F-fluorodeoxyglucose positron emission tomography and an increased maximum standardised uptake value require further investigation.