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Figure 3. This is a case of diffuse-plus-focal FDG uptake transitioned to focal uptake in a patient with Stage III melanoma. (A) Diffuse-
plus-focal FDG uptake (diffuse SUV 8.4, focal SUV 12.8) in the thyroid during treatment with interferon therapy resulting in induced
primary hypothyroidism treated with I-T4. (B) FDG uptake regressed after treatment of thyroiditis to a focal area of increased uptake in
the left thyroid lobe, SUV 9.8. Final pathology after total thyroidectomy showed multifocal papillary thyroid carcinoma.

Self-resolving variant
In our study of 6457 FDG-PET scans, we identified 103 patients with incidental focal thyroid uptake
(PETomas), and unexpectedly 5 patients (4.9%) demonstrated self-resolution of the PETomas . This
[18]
phenomenon is probably overlooked, mainly because the published data on PETomas are invariably cross-
sectional studies.

In a recent, detailed study of 47 patients with thyroid PETomas, Poller et al. could not identify any
[62]
specific cytological or histopathological cause in 14 (29.8%) of these lesions. The time frame between the
discovery of the PEToma and the final diagnosis was not mentioned. But it is conceivable that some of the
patients in this series manifested a natural history evolving towards self-resolution. The reasons underlying