Localization and identification of parapharyngeal metastases from differentiated thyroid carcinoma by 131I-SPECT/CT.

Abstract

Parapharyngeal metastasis is a rare event in differentiated thyroid carcinoma (DTC). The (131) I-single photon emission CT (SPECT)/CT allows better localization and definition for metastases in DTC. The aim of this study was to assess the value of (131) I-SPECT/CT for the diagnosis of parapharyngeal metastasis in patients with DTC. Consecutive patients with DTC (n = 561) treated with (131) I for the ablation of remnant or treatment of metastases were enrolled. A (131) I-SPECT/CT was performed when there were abnormal findings indicative of parapharyngeal metastasis on (131) I-whole-body scan (WBS). A total of 15 lesions were found to be parapharyngeal metastasis in 14 of 561 patients with DTC after the use of (131) I-SPECT/CT. The incidence rate of parapharyngeal metastasis was about 2.5% in DTC. Of the 15 lesions, only 5 lesions were CT-positive. The remaining 10 lesions were either ignored or indeterminate by the CT alone. The (131) I-SPECT/CT can identify parapharyngeal metastasis at an early stage. Parapharyngeal metastasis in DTC is relatively frequent after the use of (131) I-SPECT/CT.