Bilateral adrenal lesions showing increased 18F-FDG uptake after thyroidectomy for papillary thyroid carcinoma turned out benign: A report of three cases

Learning Objectives To present unusual cases with benign adrenal etiology showing 18F-FDG uptake that can be confused for metastasis

18F-FDG PET/CT is used to differentiate benign from malignant adrenal lesions. We present 3 cases of bilateral benign adrenal lesions showing 18F-FDG uptake in asymptomatic patients after thyroidectomy for papillary thyroid carcinoma. Thirty (A) and 46-year-old (B) female patients had total thyroidectomy and a 38-year-old (C) female patient had right lobectomy due to papillary thyroid carcinoma. Post-operative 18F-FDG PET/CTs were performed for evaluation of metastasis. In 18F-FDG PET/CTs, the bilateral adrenal glands showed 18F-FDG uptake (maximum SUV: patient A, 4.8; patient B, 5.5; patient C, 7.5) and sizes of the adrenal lesions were less than 1 cm. Adrenal CTs were done to exclude adrenal metastasis. Patient A showed normal CT finding of adrenal glands. Patient B showed 1 cm-sized bilateral adrenal nodules; the right nodule was suggestive for adrenal adenoma and the left nodule was indeterminate due to insufficient washout. Patient C showed normal CT finding in the right gland and 6 mm-sized thickening of medial limb of the left gland, which was suspicious for adrenal adenoma. 18F-FDG PET/CT scans were performed for follow-up approximately yearly. There were no interval changes in size and 18F-FDG uptake of the bilateral adrenal lesions during 43 (Patient A), 19 (Patient B) and 58 (Patient C) months. There were no presenting symptoms and laboratory abnormalities except for the low values of thyroid stimulating hormone caused by thyroidectomy or hormone replacement therapy. According to these findings, we could suggest that the etiology of these adrenal lesions was benign. In the cases of bilateral adrenal hypermetabolism in PET/CT after thyroidectomy for papillary thyroid carcinoma, the possible false-positivity for adrenal metastasis or benignancy should still be considered.