Esophageal cancer is one of the most aggressive malignancies in the world, which accounted for an estimated 572,034 new cases and 508,585 deaths in 2018 worldwide. The incidence and mortality of esophageal cancer is ranked first in China and esophageal squamous cell carcinoma (ESCC) is the main histological subtype of esophageal cancers in China. Correct preoperative evaluation of whether the tumor has reached any lymph nodes is important for management. Various methods have been used to detect primary and lymph node metastases in esophageal cancer patients, including computed tomography (CT), endoscopic examinations, and endoscopic ultrasonography (EUS). However, even such advanced imaging modalities do not always reliably identify lymph node metastasis prior to surgical resection and pathological examination.

The appearance of lymph nodes with morphological imaging procedures is classified by their shape, size, density and, if applied, contrast enhancement. BLN usually tend to have a fatty hilum, an oval shape and frequently do not measure more than 1 cm in the short axis diameter. However, the use of size as the most important criterion for differentiation of benign and malignant lymph nodes has limitations: small metastases without an increase in lymph node size are frequently missed. Positron emission tomography (PET)/computed tomography (CT) is increasingly used as single "one stop shop" method, which the combination of morphological and functional imaging represents the optimal approach for lymph node staging and general staging. A radioactive tracer，2-\[18F\]fluoro-2-deoxy-glucose (18F-FDG) currently used is based on the increased glucose metabolism, which may be reported with semiquantitative standard uptake value (SUV). Routinely, 18F-FDG is intravenous injected and PET/CT scan is performed after 60 min. The static imaging in differentiation of inflammatory from MLN may be problematic. Because inflammatory lymph nodes goes along with an increase in glucose metabolism, and thus may manifest increased 18F-FDG uptake. It was reported that PET-CT sensitivity and specificity for the detection of loco-regional metastases were moderate, but sensitivity and specificity were reasonable for distant metastases. Many researchers found there is a correlation between the 18F-FDG uptake and time. In malignancy, the uptake of FDG uptake continues to increase for several hours after FDG injection whereas such prolonged period of FDG uptake is rare in inflammatory/infectious or normal tissues. Shum et al ever assessed clinical usefulness of dual-time FDG PET/CT in esophageal squamous cell carcinoma, which turned out the sensitivity of FDG PET-CT in detecting the primary ESCC with combination of early maximum standard uptake value (SUVmax) ≥2.5 or retention index (RI) ≥10% was 96.2%. However, for loco-regional lymph node detection, there was no significant difference using dual-time 18F-FDG PET/CT assessment. Dynamic 18F-FDG PET/CT allows quantitative assessment of lesion in vivo by using a Patlak model to obtain the influx constant (Ki), and the glucose metabolic rate (MRglu). The purpose of the study is to determine whether the dynamic 18F-FDG PET/CT imaging (0-60 min) add additional value in differentiation MLN from BLN.