18F-FDG PET/CT in patients with suspected recurrent or metastatic well-differentiated thyroid cancer.

UNLABELLED: PET using 18F-FDG has been shown to effectively detect various types of cancer by their increased glucose metabolism. The aim of this study was to evaluate the use of coregistered PET and CT (PET/CT) in patients with suspected thyroid cancer recurrence. METHODS: After total thyroidectomy followed by radioiodine ablation, 61 consecutive patients with elevated thyroglobulin levels or a clinical suspicion of recurrent disease underwent 18F-FDG PET/CT. Of these, 59 patients had negative findings on radioiodine (131I) whole-body scintigraphy (WBS). Fifty-three of the 61 patients had both negative 131I WBS findings and elevated thyroglobulin levels. PET/CT images were acquired 60 min after intravenous injection of 400-610 MBq of 18F-FDG using a combined PET/CT scanner. Any increased 18F-FDG uptake was compared with the coregistered CT image to differentiate physiologic from pathologic tracer uptake. 18F-FDG PET/CT findings were correlated with the findings of histology, postradioiodine WBS, ultrasound, or clinical follow-up serving as a reference. The diagnostic accuracy of 18F-FDG PET/CT was evaluated for the entire patient group and for those patients with serum thyroglobulin levels of less than 5, 5-10, and more than 10 ng/mL. RESULTS: Thirty patients had positive findings on 18F-FDG PET/CT; 26 were true-positive and 4 were false-positive. In 2 patients, increased 18F-FDG uptake identified a second primary malignancy. 18F-FDG PET/CT results were true-negative in 19 patients and false-negative in 12 patients. The overall sensitivity, specificity, and accuracy of 18F-FDG PET/CT were 68.4%, 82.4%, and 73.8%, respectively. The sensitivities of 18F-FDG PET/CT at serum thyroglobulin levels of less than 5, 5-10, and more than 10 ng/mL were 60%, 63%, and 72%, respectively. Clinical management changed for 27 (44%) of 61 patients, including surgery, radiation therapy, or chemotherapy. CONCLUSION: Coregistered 18F-FDG PET/CT can provide precise anatomic localization of recurrent or metastatic thyroid carcinoma, leading to improved diagnostic accuracy, and can guide therapeutic management. In addition, the findings of this study suggest that further assessment of 131I WBS-negative, thyroglobulin-positive patients by 18F-FDG PET/CT may aid in the clinical management of selected cases regardless of the thyroglobulin level.

Controversial ectopic thyroid: a case report of thyroid tissue in the axilla and benign total thyroidectomy.

A 43-year-old woman presented with a mass in her left axilla, which was surgically excised. Histologically, the tissue was a reactive lymph node with adjacent thyroid follicular tissue. The differential diagnosis included benign ectopic thyroid versus metastatic well-differentiated follicular-derived thyroid carcinoma. Because of the possibility of carcinoma, the patient underwent a diagnostic total thyroidectomy. The thyroid was grossly normal with no histologic evidence of malignancy. Post-operatively, the patient underwent a whole body 131I scan. Aside from an expected residual uptake in the thyroid bed region, there was no extrathyroidal uptake to suggest additional ectopic thyroid tissue or metastatic disease. At the time of this scan, her thyrotropin (TSH) was 92.8 microU/mL, thyroglobulin was less than 0.3 ng/mL, and thyroglobulin antibody was less than 3 IU/mL. Abnormalities in the embryologic development and migration of the thyroid gland can result in ectopic thyroid tissue. The most frequent locations are along the midline from the base of the tongue to the mediastinum. Only rare case reports exist of ectopic thyroid in other locations, including the chest (heart, trachea), abdomen (liver, gallbladder, pancreas), and pelvis (vagina). This case represents the first description of thyroid tissue in the axilla with a histologically benign thyroid gland.