Preoperative Diagnostic Value of [18F] Fluorodeoxyglucose Positron Emission Tomography in Patients With Radioiodine-Negative Recurrent Well-Differentiated Thyroid Carcinoma

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Abstract
To assess the utility of 2-[18F] fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) to detect recurrent disease in the follow-up of patients with well-differentiated thyroid cancer (WDTC) who have negative diagnostic 131I scans and abnormal thyroglobulin levels. In general, patients with WDTC have an excellent long-term prognosis when appropriate surgical treatment and follow-up are carried out. After total thyroid ablation, whole-body 131I scintigraphy and measurement of serum thyroglobulin are useful diagnostic tools to detect persistent or recurrent malignancy. In case of tumor dedifferentiation, decreased or lost iodine-accumulating ability may lead to false-negative 131I scanning results. The diagnostic and therapeutic delay is responsible for a poor prognosis in this subgroup of patients. Efforts have been made in the search for suitable imaging modalities capable of early detection of recurrent thyroid carcinoma. The authors prospectively analyzed 24 patients with WDTC, negative results of whole-body 131I scintigraphy, and elevated serum thyroglobulin concentrations. Attenuation-corrected whole-body FDG-PET scans from the neck to the upper legs were performed. In addition, all patients underwent cervical ultrasonography. The results of the imaging studies were compared with histopathologic findings. If no resection of the suspicious lesion was carried out, computed tomography data were used as control criteria. Overall, FDG-PET disclosed 38 hot spots. The sensitivity of the method was 94.6%, but the specificity was lower (25.0%). The diagnostic accuracy was 87.8%. There were three false-positive results in two patients with benign cervical lymph nodes. In one patient with regional lymph node metastases in the neck, two false-negative results were obtained. Ultrasound classified both findings as malignant, however. Because of unexpected findings, FDG-PET suggested potential modification of the surgical management in nine patients. Distant metastases could be disclosed using FDG-PET in only three patients. FDG-PET is a useful diagnostic tool in the follow-up of thyroidectomized patients with WDTC, negative 131I scanning results, and abnormal serum thyroglobulin concentrations. The method detects metastatic disease in 94.6% of cases. PET results changed surgical tactics in a significant number of patients. Accurate staging of locoregional cancer recurrence in the neck may be consummately obtained by concomitant analysis of PET and ultrasound results.

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