Amy Elizabeth Musk MD, Presenter: Nothing to Disclose

Jade Janette Wong-You-Cheong MD, Abstract Co-Author: Nothing to Disclose

Faaiza Mahmoud MBBS, Abstract Co-Author: Nothing to Disclose

Vasken Dilsizian MD, Abstract Co-Author: Research Consultant, Molecular Insight Pharmaceuticals, Inc, Cambridge, MA

Incidental FDG uptake by the thyroid is detected in 1.1-4.3% of whole body PET scans performed for staging non thyroid cancer, with 29-80% of these lesions malignant at tissue diagnosis. Because this was contrary to our experience, we performed this study to determine the frequency and significance of incidental increased FDG thyroid uptake.

The databases of the nuclear medicine and radiology departments were searched for whole body FDG-PET and PET-CT scans performed between September 1, 2000 and January 31, 2007. Reports describing abnormal thyroid uptake were extracted. The patient medical record and radiology studies were evaluated for correlative imaging studies, and findings at PET, fine needle aspiration biopsy or surgery. Patients with thyroid cancer were excluded.

3004 patients underwent PET/PET-CT staging scans. 39 (1.3 %) patients had unexpected metabolic activity in the thyroid gland and formed the study group. Findings at PET were: focal uptake n= 18, diffuse/ill defined uptake n=21; SUV range 1.9 – 40.1. 13 patients underwent a total of 14 samplings by ultrasound guided fine needle aspiration followed by surgical resection in 6. Ultrasound findings were focal solid nodules in 4 patients, mixed solid/cystic nodule in 6, and 3 patients had diffusely abnormal texture. Four nodules were benign adenomatoid/colloid nodules (mean SUV 2.6), 4 were indeterminate follicular lesions (SUV moderate-high), 3 were inflammatory thyroiditis (SUV 5.3), one indeterminate (SUV 5.5), and 2 lesions was suspicious for papillary thyroid neoplasm (mean SUV 2.7 ). At surgery, 1 of the indeterminate follicular neoplasms was follicular/Hurthle cell carcinoma, 1 was follicular variant of papillary carcinoma, and the other 2 were follicular adenomas. Of the 2 suspicious for papillary neoplasm, 1 was lymphocytic thyroiditis, and the other was colloid nodule with cystic degeneration/hemorrhage.

Incidental thyroid FDG uptake was found in 1.3% of patients with cancer. When biopsied, 15% of these nodules were malignant. SUV values did not correlate with malignancy risk.

Further workup is needed to determine the significance of incidental increased thyroid uptake on FDG-PET scans.

Musk, A, Wong-You-Cheong, J, Mahmoud, F, Dilsizian, V, The Significance of Thyroid Incidentalomas Detected on FDG-PET Scans in Patients with Cancer.  Radiological Society of North America 2007 Scientific Assembly and Annual Meeting, November 25 - November 30, 2007 ,Chicago IL. http://archive.rsna.org/2007/5007273.html