Aim: Differentiated thyroid carcinoma has a favorable prognosis, even in the presence of distant metastases, if the tumor cells are able to concentrate radioiodine. Nonetheless, up to 30% of thyroid cancer patients with elevated serum thyroglobulin (Tg) and negative radioiodine whole-body scan findings represent a diagnostic dilemma. In this study we assessed the diagnostic contribution of anatomical and functional imaging procedures, including US of the thyroid bed and neck, CT scanning of the chest and mediastinum, and FDG PET whole-body scanning, in iodine-negative/Tg-positive thyroid cancer patients. Materials and methods: The study included 28 patients (20 female, 8 male; age range: 21-85 years; mean age: 56 years) with a proven diagnosis of thyroid carcinoma. The pathological diagnosis was papillary carcinoma in 26 patients, and Hurtle-cell carcinoma and poorly differentiated thyroid carcinoma, respectively, in the 2 remaining patients. All patients had undergone thyroid surgery and subsequent high-dose radioablation 3-8 years before participating in the study. In all, 27 patients presented with elevated serum Tg levels (3.1-3080 ng/mL, median 93) and 1 presented with multiple metastatic lesions in the lungs, despite the fact that Tg was within normal limits. All patients had a US examination of the thyroid bed and neck to determine if locoregional persistent disease was present. The patients were scheduled for high-dose radioiodine treatment because Tg was elevated after cessation of L-thyroxin for approximately 6 weeks. Those with a negative or equivocal post-treatment scan proceeded to whole-body 18-fluorodeoxyglucose PET. We assessed the diagnostic contribution of imaging procedures, including US of the thyroid bed and neck, CT of the chest and mediastinum, and PET, in patients that presented with elevated Tg levels and negative radioiodine scanning. Results: In total, 62 tumor sites were identified in the thyroid bed and neck (7 patients), lung and mediastinum (6 patients), both in the neck and lungs (5 patients), lung and bone (2 patients), neck and bone (1 patient), and neck, lung, and bone (1 patient). In 6 patients no thyroid tumor was detected with any imaging modality. US was useful in detecting cervical lymph nodes in 14 patients and CT revealed metastatic foci in the lung and mediastinum, and bone in 15 patients. In 25 patients post-treatment scanning was negative and in 3 there was faint uptake in the neck. FDG-PET revealed thyroid tumor sites in 18 patients; however, it was false-positive in 3 cases and missed 2 cervical adenopathies and 1 metastatic bone lesion. Conclusion: US and CT provided diagnostic information for detecting cervical adenopathy and metastatic lesions in the lungs and mediastinum, respectively. PET complemented the existing anatomical findings and enabled whole-body scanning in a single imaging session. It was particularly useful in detecting iodine-negative differentiated thyroid cancer associated with elevated serum Tg levels, thereby facilitating appropriate treatment.

Aim: Differentiated thyroid carcinoma has a favorable prognosis, even in the presence of distant metastases, if the tumor cells are able to concentrate radioiodine. Nonetheless, up to 30% of thyroid cancer patients with elevated serum thyroglobulin (Tg) and negative radioiodine whole-body scan findings represent a diagnostic dilemma. In this study we assessed the diagnostic contribution of anatomical and functional imaging procedures, including US of the thyroid bed and neck, CT scanning of the chest and mediastinum, and FDG PET whole-body scanning, in iodine-negative/Tg-positive thyroid cancer patients. Materials and methods: The study included 28 patients (20 female, 8 male; age range: 21-85 years; mean age: 56 years) with a proven diagnosis of thyroid carcinoma. The pathological diagnosis was papillary carcinoma in 26 patients, and Hurtle-cell carcinoma and poorly differentiated thyroid carcinoma, respectively, in the 2 remaining patients. All patients had undergone thyroid surgery and subsequent high-dose radioablation 3-8 years before participating in the study. In all, 27 patients presented with elevated serum Tg levels (3.1-3080 ng/mL, median 93) and 1 presented with multiple metastatic lesions in the lungs, despite the fact that Tg was within normal limits. All patients had a US examination of the thyroid bed and neck to determine if locoregional persistent disease was present. The patients were scheduled for high-dose radioiodine treatment because Tg was elevated after cessation of L-thyroxin for approximately 6 weeks. Those with a negative or equivocal post-treatment scan proceeded to whole-body 18-fluorodeoxyglucose PET. We assessed the diagnostic contribution of imaging procedures, including US of the thyroid bed and neck, CT of the chest and mediastinum, and PET, in patients that presented with elevated Tg levels and negative radioiodine scanning. Results: In total, 62 tumor sites were identified in the thyroid bed and neck (7 patients), lung and mediastinum (6 patients), both in the neck and lungs (5 patients), lung and bone (2 patients), neck and bone (1 patient), and neck, lung, and bone (1 patient). In 6 patients no thyroid tumor was detected with any imaging modality. US was useful in detecting cervical lymph nodes in 14 patients and CT revealed metastatic foci in the lung and mediastinum, and bone in 15 patients. In 25 patients post-treatment scanning was negative and in 3 there was faint uptake in the neck. FDG-PET revealed thyroid tumor sites in 18 patients; however, it was false-positive in 3 cases and missed 2 cervical adenopathies and 1 metastatic bone lesion. Conclusion: US and CT provided diagnostic information for detecting cervical adenopathy and metastatic lesions in the lungs and mediastinum, respectively. PET complemented the existing anatomical findings and enabled whole-body scanning in a single imaging session. It was particularly useful in detecting iodine-negative differentiated thyroid cancer associated with elevated serum Tg levels, thereby facilitating appropriate treatment.