Preoperative Lymph Node Staging by FDG PET/CT With Contrast Enhancement for Thyroid Cancer: A Multicenter Study and Comparison With Neck CT

Abstract

Objectives: The purpose of this study was to compare lymph node (LN) staging using ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) with contrast-enhancement (CE) PET/CT and contrast-enhanced neck CT (neck CT) in patients with thyroid cancer with level-by-level comparison with various factors.

Methods: This was a retrospective multicenter study. A total of 85 patients were enrolled. Patients who underwent a preoperative evaluation by CE PET/CT and neck CT for thyroid cancer were enrolled. The gold standard for LN was the combination of surgical pathology and clinical follow-up. We compared CE PET/CT with neck CT using a level-by-level method. Factors, including age, sex, camera, arm position, tumor size, extra-thyroidal extension, tumor location, number of primary tumors, primary tumor maximum standardized uptake value, and the interval from scan to operation were also analyzed.

Results: Overall accuracy was 81.2% for CE PET/CT and 68.2% for neck CT. CE PET/CT was more sensitive than neck CT (65.8% vs. 44.7%). Also, CE PET/CT showed higher negative predictive value (77.2% vs. 66.1%). CE PET/CT showed good agreement with the gold standard (weighted kappa [κ], 0.7) for differentiating N0, N1a, and N1b, whereas neck CT showed moderate agreement (weighted κ, 0.5). CE PET/CT showed better agreement for the number of levels involved with the gold standard (weighted κ, 0.7) than that of neck CT with the gold standard (weighted κ, 0.5). The accuracies for differentiating N0, N1a, and N1b were 81.2% for CE PET/CT and 68.2% for neck CT. Level-by-level analysis showed that CE PET/CT was more sensitive and has higher negative predictive value for detecting ipsilateral level IV and level VI LNs than neck CT. Other analyzed factors were not related to accuracies of both modalities.

Conclusion: CE PET/CT was more sensitive and reliable than neck CT for preoperative LN staging in patients with thyroid cancer.

Keywords: Computed Tomography; Fluorodeoxyglucose F18; Positron-Emission Tomography; Thyroid Neoplasms.

Fig. 1.

A case of different finding of ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography with contrast-enhancement (CE PET/CT) and contrast-enhanced neck CT (neck CT) in a preoperative lymph node staging in a patient with thyroid cancer. A 56-year-old female patient underwent CE PET/CT and neck CT with contrast-enhancement before thyroid cancer operation: (A) maximum intensity image of CE PET/CT, (B, C) axial fusion images, (D) axial PET only image at the same level of C, and (E) axial image of neck CT. A calcified nodule with focal hypermetabolism with maximum standardized uptake value (SUVmax) 4.2 was found in left thyroid lobe which was proven to be papillary cancer by fine needle aspiration (arrow in B). Both of CE PET/CT and neck CT showed a lymph node adjacent to left carotid vessel (arrows in C-E). The long diameter by neck CT was about 1 cm (E), suggesting metastatic lymph node. However, FDG uptake was not high (arrows in D, SUVmax 1.4), suggesting benign feature. After operation, biopsy revealed benign lymph node. Also, clinical follow-up with radioactive iodine scan and neck ultrasonography (images not shown), there was no metastatic lymph node.