Background: This study was designed to evaluate the performance of ultrasonography (US) for the preoperative staging of papillary thyroid carcinoma (PTC) in a large series according to the TNM classification. Methods: Preoperative US was performed for the evaluation of primary tumors and lymph node metastasis in 722 consecutive patients with cytologically proven PTC. Three experienced radiologists prospectively determined T and N categories of PTC. N categorization was based on compartments, including left and right lateral compartments (levels II-V) and central compartment (level VI). All patients underwent surgery and central compartment dissection. Lateral compartment dissection was selectively performed. We assessed the diagnostic performance of preoperative US for staging of PTC on the basis of pathologic findings of surgical specimens. Subgroup analysis according to suspicion of diffuse thyroid disease (DTD) on US was performed to compare US accuracies for N categorization. Results: US predicted 61.7% (142/230) of patients with multifocal PTC and 67.1% (100/149) of patients with bilateral malignancy. Overall accuracy of US for T categorization was 69.7% (503/722) and that of US for N categorization was 59% (426/722). Accuracies of sonographic categorization for N0, N1a, and N1b were 66% (276/418), 33.3% (70/210), and 85.1% (80/94), respectively. Overall US accuracy for prediction of an N category was significantly lower in patients with US-indicated DTD (51.1%, 67/131) than it was in patients without DTD (60.7%, 359/591; P = 0.043). Conclusions: Preoperative US is a feasible technique for the preoperative staging of PTC and is helpful for the detection of lateral compartment metastasis. Presence of DTD can affect the staging of lymph node metastasis.
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