Diagnostic performance of preoperative FDG-PET for the detection of metastatic cervical lymph nodes in recurrent papillary thyroid carcinoma patients with negative I-131 whole body scans

Abstract

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Objectives: We evaluated the diagnostic performance of FDG-PET for the detection of metastatic cervical lymph nodes in recurrent papillary thyroid carcinoma patients with negative I-131 scan. Methods: Nineteen patients with papillary thyroid carcinoma who had total thyroidectomy and I-131 ablation therapy were included. In the follow-up period, FDG-PET showed suspected cervical lymph nodes metastases and neck dissection was performed within 3 months after FDG-PET. They were negative on I-131 WBS, but showed suspicious metastatic findings on FDG-PET, CT scan, and US. Except for patients with elevated Tg antiboby levels, all patients showed the serum Tg levels ≥10ng/ml (83.2 ± 119.1) at the TSH of ≥30uIU/ml. Pathologic results of lymph nodes were compared with FDG-PET findings. The size of lymph node was measured by preoperative CT scan or US. Results: In 45 cervical lymph node groups dissected, 31 lymph node groups were metastasis. The sensitivity and specificity of FDG-PET for metastasis were 74.2% (23 of 31) and 50.0% (7 of 14), respectively. Eight lesions with metastasis showed no abnormal FDG uptake (false negative), and none of them exceeded 8mm in size (4 to 8mm, median= 6mm). On the other hand, twenty-three metastatic lesions with abnormal FDG uptake (true positive) were variable in size (6 to 17mm, median=9mm). Conclusions: FDG-PET is suitable for the detection of metastatic cervical lymph nodes in patients with negative I-131 scan. However, small sized lymph nodes could not be detected on FDG-PET.