BACKGROUND: The value of PET/CT imaging in diagnosis
of different cancers has been widely described. PET/CT may
contribute to visualization of additional findings that were not
the indication to the study and did not refer to initial diagnosis.
In a small number of PET/CT scans an incidentally found focal
18F-FDG uptake in the thyroid gland is found.
The goal of the study was to estimate the prevalence
and evaluate the clinical significance of incidental thyroid
18F-FDG uptake in a cohort of patients diagnosed for different
malignancies.
MATERIAL AND METHODS: 2478 PET/CT scans using 18F-FDG
were performed in 1925 subjects for evaluation of different,
non-thyroid malignancies. For PET/CT examination, a Discovery
ST (General Electric) PET/CT scanner was used. Patients with
focal 18F-FDG activity were further evaluated by means of fine
needle aspiration biopsy (FNAB). If cytological examination
disclosed malignancy or suspicion of malignancy, thyroidectomy was performed. Both cytological and histopathological results
were then analyzed.
RESULTS: Focal increased 18F-FDG uptake was found in 71
patients (3.7%), and cytological or histopathological results were
evaluable in 20 of them. In general, 8 cases of thyroid cancer
were found, which accounts for 40% probability of malignancy.
The predominant histopathological diagnosis was papillary
thyroid carcinoma (5 out of 8 cases). Additionally, in one case
(5%) thyroid metastasis of lung cancer was detected.
Diffused 18F-FDG activity in both thyroid lobes was observed
in 120 subjects (6.2%) — in most cases chronic thyroiditis was
confirmed.
CONCLUSIONS: The probability of malignancy of focal thyroid
incidentalomas in 18F-FDG PET/CT scans is rather high. Therefore,
thorough evaluation of such lesions is highly recommended
in each case. Most thyroid malignancies incidentally detected
in PET/CT are papillary carcinomas.
Nuclear Med Rev 2011; 14, 2: 68–7