Right liver metastasis was detected at follow-up ultrasound. PET-CT was ordered to stage the disease and to look for extra-hepatic metastases.

Coronal view of whole-body FDG-PET showed high uptake in the large liver lesion, and an additional hot spot in the right and anterior part of the cervical region. 

The PET-CT fusion image shows that the hot spot is located in the right lobe of the thyroid gland. 

Teaching point.

Incidental thyroid uptake is observed in 2-4% of patients undergoing FDG PET. The pattern of uptake can be focal, diffuse, or a mix of both. Focal uptake corresponds to malignant disease in 14 to 47% of the cases, and thus must not be overlooked nor disregarded. In a recent paper published in the JNM (2006;47:609-615) , Choi et al showed that a combined PET and CT set of criteria increased the diagnostic accuracy. SUV alone cannot discriminate benign from malignant lesions. But the combination of focal uptake, corresponding nodule with low attenuation on CT and a SUV>4.2 yielded a sensitivity of 90%.

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