Objective:To compare the 99Tc m-dextran(DX) lymphoscitigraphy and direct lymphography (DLG), in order to investigate the imaging features and clinical significance of 99Tc m-DX lymphoscitigraphy in patients with thoracic duct exports (TDE)obstruction. Methods:A total of 304 patients (140 males, 164 females, median age: 32 years) with TDE obstruction confirmed by thoracic duct exploration between 2017-01-01 and 2019-01-01 in Beijing Shijitan Hospital were retrospectively analyzed. Based on the different imaging characteristics of TDE, the reluts of 99Tc m-DX lymphoscitigraphy were divided into five groups (Ⅰ: no TDE presenting; Ⅱ: TDE presenting temporarily; Ⅲ: TDE presenting constantly or extensively; Ⅳ: abnormal reflux of imaging agents; Ⅴ: bilateral venous angle presenting). Ⅰ/Ⅱ groups were regarded as negative and Ⅲ-Ⅴ groups as positive. The consistency of 99Tc m-DX lymphoscitigraphy with DLG was evaluated with Kappa test, and the positive rates of the two methods were compared by McNemar test. Results:In the detection of TDE, the positive rate of 99Tc m-DX lymphoscintigraphy was 70.1% (213/304), which was significantly lower than that of DLG (97.4%, 296/304; χ2=4.16, P<0.001). The group Ⅲ has the largest number of cases (54.9%, 167/304), and there was a low consistency with DLG ( Kappa=0.08, P=0.005). However, there was a higher consistency between 99Tc m-DX lymphoscintigraphy results and the corresponding DLG results in the groups Ⅳ/Ⅴ ( Kappa values: 0.48, 0.86, both P<0.001). Furthermore, the diagnostic accordance rates of lower extremity lymphedema and chylous effusion were 96.1%(98/102) and 83.6%(127/152), respectively, compared with the clinical diagnosis. Conclusions:TDE obstruction of 99Tc m-DX lymphoscitigraphy presents in the majority with Ⅲ type. 99Tc m-DX lymphoscitigraphy results in patients with type Ⅳ and Ⅴ have a better consistency with those of DLG. 99Tc m-DX lymphoscitigraphy can be used as a screening tool of TDE obstruction, and play a role in the diagnosis of lower limb lymphedema and chylous effusion caused by TDE obstruction.