Thyroid Cancer - 56 year old female

History
56 year old female with a history of papillary thyroid carcinoma, status post thyroidectomy with rising thyroglobulin level and negative I-131 scan. Patient presents for a restaging PET/CT.

Nuclear Medicine I-131 Imaging Findings
Total body images as well as spot images were obtained with no apparent abnormal areas of uptake of I-131.

PET/CT Findings
There is a focal area of moderate to intense increased uptake of FDG in the left neck inferiorly, corresponding to a small left level 4 lymph node on the CT portion of the exam.

Discussion
In October of 2003, re-staging of thyroid cancer was approved for PET or PET/CT coverage by Medicare and most third party payers. In general, we do not use PET/CT for the evaluation of primary disease or for staging because many of these tumors will be relatively non-FDG avid. There is a well-known flip-flop phenomenon, wherein a tumor that is iodine avid tends to be FDG negative and tumors that are not iodine sensitive tend to be FDG avid. Of course, there is some overlap.

The patients that we use PET/CT to evaluate are patients with a history of thyroid malignancy, have had a thyroidectomy and have had a negative I-131 and rising thyroglobulin levels. These patients may have at one time had iodine avid disease, but once their tumors have dedifferentiated, they often become negative on I-131. Many of these patients, as described above, will be positive on PET or PET/CT. We have had great success in localizing small or occult disease in this patient population.

In this particular case, a small normal appearing jugulodigastric lymph node was found to have FDG uptake and was subsequently resected and found to be positive for recurrent papillary carcinoma.

Courtesy of
Todd Blodgett, MD, University of Pittsburgh Medical Center