Prediction of central lymph node metastasis from papillary thyroid microcarcinoma by 18F-fluorodeoxyglucose PET/CT and ultrasonography.

PURPOSE: The presence of central lymph node (LN) metastasis increases the risk of cervical LN recurrence or distant metastasis in patients with papillary thyroid microcarcinoma (PTMC). We investigated the value of preoperative (18)F-fluoro-2-deoxy-D-glucose-positron emission tomography (FDG PET)-computerized tomography (CT) and ultrasonography (US) to predict central LN metastasis from PTMC.

PATIENTS AND METHODS: Two hundred patients with newly diagnosed unifocal PTMC were enrolled. Preoperative FDG PET-CT was performed, and the highest SUV (SUV(max)) of focally increased uptake at thyroid was measured. Tumor size was measured using preoperative US. Uni- and multivariate analyses were performed using the presence of focally increased uptake at thyroid (FDG positivity), SUV(max), tumor size, and clinical risk factor for central LN metastasis. ROC curves for risk factors were then analyzed. These analyses were undertaken in two groups: the all patients group and the FDG-positive group. Finally, we combined risk factors associated with central LN metastasis to improve predictive accuracy.

RESULTS: Tumor size >6 mm was associated with central LN metastasis. FDG positivity was identified in 110 patients (55.0%) and the SUV(max) ranged from 1.8 to 12.8 (median 3.0). In FDG-positive group, SUV(max) >2.8 was associated with central LN metastasis. Addition of SUV(max) >2.8 to size >6 mm of PTMC improved sensitivity of predicting central LN metastasis from 55.0 to 67.5%, while specificity remained at 70.6%.

CONCLUSION: Both FDG PET-CT and US are valuable for preoperative prediction of central LN metastasis from PTMC. Combined use of SUV(max) and tumor size improves sensitivity without changing specificity.