Chirag Jethva, Presenter: Nothing to Disclose

Sankaran Shrikanthan MD, Abstract Co-Author: Nothing to Disclose

Donald Richard Neumann MD, PhD, Abstract Co-Author: Nothing to Disclose

Shyam Srinivas MD, PhD, Abstract Co-Author: Nothing to Disclose

To determine if diffuse versus focal FDG uptake in the thryoid gland found incidentally in subjects on PET/CT can differentiate between the presence of a benign versus malignant disease process. It is postulated that subjects with diffuse uptake will be likely affected by a benign condition, while the subjects with focal uptake may have a thyroid malignancy.

1124 subjects from an IRB-approved PET/CT oncologic database were evaluated for the presence of FDG uptake in the thyroid gland. Out of these 1124 subjects, 46 subjects (4%) were found to have incidental thyroid uptake. Those with diffuse uptake had an average SUV weighted by the volume of each thyroid lobe. VOIs were drawn using the anatomical border on CT scan. In subjects who showed focal uptake, the max SUV was measured. Recent TSH values and supplemental thyroid hormone therapy were documented.

27 out of the 46 subjects (59%) showed diffuse thyroid uptake and the other 19 subjects (41%) exhibited focal thyroid uptake. Of the 27 subjects who demonstrated diffuse uptake, 20 (74%) were found to be hypothyroid, based on elevated TSH values or by supplemental thyroid hormone therapy. None of these patients were diagnosed with a thyroid malignancy. Average SUVs in diffuse thyroids ranged from 1.8 to 5.4. Of the 19 subjects who had focal thyroid uptake, 12 had distinct thyroid nodules demonstrated on corresponding CT images, while 7 did not. Four of the 19 subjects (21%) with focal uptake were found to be hypothyroid. One of these 19 subjects had biopsy proven benign follicular hyperplasia (Max SUV = 3.8) and one had biopsy proven papillary thyroid cancer (Max SUV = 15.1).

Thyroid FDG uptake, either diffuse or focal, is a relatively uncommom finding on FDG-PET/CT. When diffuse thyroid uptake is found, it is predominantly due to hypothyroidism. No cases of Graves' disease, acute/subacute thyroiditis, or malignancy were found in this population. In the instance of focal thyroid uptake, more follow up data is required to draw conclusions, however the possibility of thyroid cancer must be considered.

Incidental thyroid FDG uptake is seen with varying patterns and uncertain clinical significance on PET/CT. This study seeks to correlate particular thyroid FDG scan patterns with pathological state.

Jethva, C, Shrikanthan, S, Neumann, D, Srinivas, S, Diffuse versus Focal Uptake in the Thyroid Gland on FDG-PET/CT: What Does It Mean?.  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/6012893.html