This is a single-center diagnostic accuracy study, with the purpose to define the criteria to diagnose small cervical lymph node metastases in patients with nasopharyngeal carcinoma by combining MRI scanning and contrast-enhanced ultrasonography and evaluate the diagnostic performance of the criteria.

For newly diagnosed and histologically confirmed nasopharyngeal carcinoma patients staged as T1-4, N0-1/N3, M0 (AJCC 8th), if no metastatic lymph nodes were found on MRI according to the current diagnostic criteria, but there were small lymph nodes with a minimal axial diameter ≥ 5 mm (6 mm for lymph node in level IIA) on at least one side of the patient's neck, they will be eligible for this study. The MRI image of the small lymph nodes will be evaluated in details by experienced radiologists. Contrast-enhanced ultrasonography with specific ultrasound contrast agents (Sonazoid) and ultrasound-guided lymph node aspiration will be performed. Subsequently, the lymph node tissue obtained from ultrasound-guided lymph node aspiration will be subjected to pathologic evaluation. Using the pathologic diagnosis of the lymph node as the gold standard, diagnostic performance of MRI and contrast-enhanced ultrasonography will be evaluated. Resonable criteria to diagnose small cervical lymph node metastases by combining MRI scanning and contrast-enhanced ultrasonography will be explored. And the diagnostic performance of the criteria will be evaluated.

Inclusion Criteria:

1. Eastern Cooperative Oncology Group performance status ≤1;
2. Patients with histologically confirmed nasopharyngeal carcinoma;
3. Tumor staged as T1-4, N0-1/N3, M0 (AJCC 8th);
4. On at least one side of the patient's neck, no metastatic lymph nodes were found on MRI according to the current diagnostic criteria, but there were small lymph nodes with a minimal axial diameter ≥ 5 mm (6 mm for lymph node in level IIA);
5. Patients must be informed of the investigational nature of this study and give written informed consent. And they should be willing and able to comply with the requirements of examination, treatment, follow-up and other research requirements stipulated in the research schedule.

Exclusion Criteria:

1. History of other malignant tumors, except for adequately treated basal cell carcinoma, squamous cell carcinoma and cervical carcinoma in situ;
2. Previous radiotherapy, except radiotherapy for non-melanoma skin cancer outside the neck or nasopharyngeal regions;
3. Patients with coexistent head and neck squamous cell carcinoma besides nasopharyngeal carcinoma;
4. Patients with coexistent acute inflammation or infection (including infection within the area for aspiration);
5. Previous surgery or trauma within the neck or nasopharyngeal regions;
6. Not suitable for aspiration due to abnormal coagulation function;
7. All the candidate small lymph nodes with a minimal axial diameter ≥ 5 mm (6 mm for lymph node in level IIA) were not suitable for aspiration owing to high risk of severe complications after the aspiration；
8. Contraindications for the examination specified in the research schedule due to claustrophobia, the presence of metal implants or pacemaker, and allergic hypersensitivity to ultrasound contrast agents or MRI contrast agents;
9. Other situation assessed by the investigators that may compromise the safety or compliance of patients, such as serious disease requiring timely treatment (including mental illness), severe laboratory abnormalities, or family-social risk factors.