To investigate the distribution patterns and ultrasonographic features of cervical lymph node metastasis in postoperative papillary thyroid carcinoma (PTC) patients, as well as the diagnostic performance of ultrasound, in order to provide evidence for postoperative surveillance and clinical decision-making.

A retrospective analysis was conducted on 97 patients with papillary thyroid carcinoma who underwent postoperative follow-up at Sichuan Cancer Hospital from January 2023 to April 2025 and were found to have suspicious cervical lymph node metastasis on ultrasound and subsequently confirmed by pathology. Based on the pathology, the ultrasound-identified suspiciously malignant lymph nodes were divided into the malignant group and the benign group. The regional distribution of recurrent lymph nodes, ultrasonographic features, and clinical data were recorded. For intergroup comparisons, the t-test or Kruskal-Wallis H test was used for continuous variables, and the χ² test or Fisher's exact test (when applicable) was used for categorical variables. The diagnostic performance of conventional ultrasound for each cervical compartment, the impact of initial surgical dissection extent on subsequent recurrence sites, the ultrasonographic features of benign versus malignant lymph nodes, and the differences in ultrasonographic features of malignant lymph nodes between different compartments were evaluated. Receiver operating characteristic (ROC) curve analysis was performed, and the area under the curve (AUC) values were compared using the DeLong test.

Among the 97 patients included, lymph node metastases were most commonly observed in levelⅣ (60.82%) and levelⅢ (57.73%). Vascular patterns were effective indicators for differentiating benign from malignant lymph nodes: the malignant group exhibited a higher proportion of mixed/peripheral vascular pattern (Fisher's exact test, P＜0.001) and Adler grade 2-3 blood flow (χ²=14.36, P＜0.001). Metastatic lymph nodes in the central compartment had smaller diameters [(12.36±5.22) mm vs (16.96±6.93)mm, t=4.64, P＜0.001] and lower proportions of typical malignant ultrasonographic features, including hyperechoic foci (10.00% vs 33.71%; χ²=8.15, P=0.004), mixed/peripheral vascular pattern (7.50%/35.00% vs 26.97%/48.88%; χ²=21.69, P＜0.001), and Adler grade 2-3 blood flow (35.00% vs 66.29%; χ²=12.63, P＜0.001). Ultrasound demonstrated a high diagnostic sensitivity for levelⅢ (87.50%) and levelⅣ (89.83%), but a low sensitivity for levelⅡ (55.00%) and levelⅤ (52.17%). ROC curve analysis showed that the diagnostic performance for levelⅢ (AUC=0.901), levelⅣ (AUC=0.897), and levelⅥ (AUC=0.866) was superior to that for levelⅡ (AUC=0.731) (Z=3.172, 3.033, and 2.306; P=0.002, 0.002, and 0.021, respectively), and the performance for levelⅢand levelⅣ was also superior to that for levelⅤ (AUC=0.741) (Z=2.570 and 2.466; P=0.010 and 0.014, respectively). Patients who initially underwent central compartment dissection alone had a significantly higher recurrence rate in levelⅡ compared to those who received combined lateral neck dissection (55.00% vs 31.58%, P=0.021).

Postoperative recurrent lymph nodes in PTC are predominantly located in levels ⅢandⅣ, where ultrasound exhibits excellent diagnostic performance. Mixed vascular pattern and high Adler grade are important indicators for differentiating malignant from benign lymph nodes. However, the diagnostic efficacy of ultrasound for levelsⅡandⅤ is relatively limited, necessitating comprehensive evaluation incorporating multi-level signs during follow-up to avoid missed diagnosis.