Validation of CT-Based Risk Stratification System for Lymph Node Metastasis in Patients With Thyroid Cancer

Abstract

Objective: To evaluate the computed tomography (CT) features for diagnosing metastatic cervical lymph nodes (LNs) in patients with differentiated thyroid cancer (DTC) and validate the CT-based risk stratification system suggested by the Korean Thyroid Imaging Reporting and Data System (K-TIRADS) guidelines.

Materials and methods: A total of 463 LNs from 399 patients with DTC who underwent preoperative CT staging and ultrasound-guided fine-needle aspiration were included. The following CT features for each LN were evaluated: absence of hilum, cystic changes, calcification, strong enhancement, and heterogeneous enhancement. Multivariable logistic regression analysis was performed to identify independent CT features associated with metastatic LNs, and their diagnostic performances were evaluated. LNs were classified into probably benign, indeterminate, and suspicious categories according to the K-TIRADS and the modified LN classification proposed in our study. The diagnostic performance of both classification systems was compared using the exact McNemar and Kosinski tests.

Results: The absence of hilum (odds ratio [OR], 4.859; 95% confidence interval [CI], 1.593-14.823; P = 0.005), strong enhancement (OR, 28.755; 95% CI, 12.719-65.007; P < 0.001), and cystic changes (OR, 46.157; 95% CI, 5.07-420.234; P = 0.001) were independently associated with metastatic LNs. All LNs showing calcification were diagnosed as metastases. Heterogeneous enhancement did not show a significant independent association with metastatic LNs. Strong enhancement, calcification, and cystic changes showed moderate to high specificity (70.1%-100%) and positive predictive value (PPV) (91.8%-100%). The absence of the hilum showed high sensitivity (97.8%) but low specificity (34.0%). The modified LN classification, which excluded heterogeneous enhancement from the K-TIRADS, demonstrated higher specificity (70.1% vs. 62.9%, P = 0.016) and PPV (92.5% vs. 90.9%, P = 0.011) than the K-TIRADS.

Conclusion: Excluding heterogeneous enhancement as a suspicious feature resulted in a higher specificity and PPV for diagnosing metastatic LNs than the K-TIRADS. Our research results may provide a basis for revising the LN classification in future guidelines.

Keywords: Computed tomography; Lymph node; Metastasis; Thyroid; Thyroid cancer.

Fig. 1. Flow chart of the study population. FNA = fine needle aspiration, CT = computed tomography

Fig. 2. Axial computed tomography scan shows a lymph node with preserved hilar fat and hilar vessels but no internal cystic changes, heterogeneous enhancement, calcification, or strong enhancement (arrow). This lymph node would be classified into a probably benign category according to K-TIRADS. K-TIRADS = Korean Thyroid Imaging Reporting and Data System

Fig. 3. Axial computed tomography scan shows a lymph node without a hilar structure, internal cystic changes, heterogeneous enhancement, calcification, or strong enhancement (arrow). This lymph node would be classified into an indeterminate category according to K-TIRADS. K-TIRADS = Korean Thyroid Imaging Reporting and Data System

Fig. 4. Axial computed tomography scan shows a lymph node with cystic change with an eccentric strong enhancing solid portion that gives the lymph node a heterogeneous enhancement pattern (arrow). No normal hilar structure can be seen. This lymph node would be classified into a suspicious category according to K-TIRADS. K-TIRADS = Korean Thyroid Imaging Reporting and Data System.

Fig. 5. In axial precontrast computed tomography scan (A), the lymph node contains discrete calcification (arrow), and in the postcontrast enhancement image (B), the lymph node shows strong and heterogeneous enhancement without hilar structure (arrow)