The main symptoms of patients with MTS accompanying iliac vein compression are acute pain and swelling of the lower left extremity . However, they also present symptoms, such as venous claudication, chronic venous insufficiency, lipodermatosclerosis, recurrent superficial venous thrombophlebitis, and PE . For acute DVT, early recanalization is highly important and plays an important role in preventing PTS. In current MTS treatment plans, endovascular therapy, including CDT, PMT, and stent placement, is commonly applied with satisfactory results [8,9].
Despite the fact that patients with MTS commonly present with DVT, PE is rarely found in these patients. Few studies have examined the correlation between stenosis extent and PE in patients with MTS. However, Chan et al.  claimed that left common iliac vein narrowing protects against symptomatic PE by trapping large emboli, analogous to an IVC filter. In particular, this study reported that significant iliac vein stenosis >70% or <4 mm in luminal diameter have a significantly lower odds of developing symptomatic PE 5]. In MTS, the stenotic lesion prevents the passage of the thrombus into the IVC and thereby lowers the frequency of PE . Only small embolic fragments pass through the stenotic lesion, and these do not lead to symptomatic PE . In this study, severe stenosis of the left iliac vein caused by MTS was associated with a better protective effect against the development of TBIVS. Also, TBIVS was associated with the development of PE at the time of presentation. This study aimed to explain that, depending on the state of the iliac vein stenosis, the state of cephalad migration of the distal thrombus can change beyond preventing a stenotic lesion, thus influencing the development of PE.
Apart from data on MTS with TBIVS, few data are available on IVC thrombosis. IVC thrombosis is rarely seen in patients with lower-extremity DVT . Risk factors of IVC thrombosis are an unretrieved IVC filter, bilateral DVT, iliofemoral DVT, IVC congenital anomaly, severe PTS, and renal cell carcinoma, among others . The mortality rate of IVC thrombosis is reportedly twice higher than that of lower-extremity DVT . Without proper treatment, PTS, PE, and disabling venous claudication, occurring at prevalence rates of 90%, 30%, and 45%, respectively, reportedly develop in patients with IVC thrombosis [12,13]. MTS with TBIVS and IVC thrombosis may differ pathophysiologically but can be observed as part of IVC thrombosis. This study showed that many patients with MTS and TBIVS presented with PE but are not expected to show high morbidity and mortality rates like those seen in IVC thrombosis.
Here we compared MTS with and MTS without TBIVS. To identify the predictors of TBIVS, binary logistic regression was performed. The greater the stenosis size, the higher the incidence of TBIVS. This study has limitations, including its small sample size and insufficient predictive values in a single center. This study only included patients who underwent an endovascular procedure; thus, it could not represent the entire cohort of patients with MTS. However, unlike general DVT, in MTS due to a structural abnormality, the fact that the iliac vein size of the stenosis has a greater effect on thrombus extension than patient status is important in diagnosis and prognosis. In this study, five patients without TBIVS did not undergo iliac venous stent placement because the stenosis was not severe on venography. We understand TBIVS as the process of thrombus progression and believe that various factors, such as vessel angulation and medical conditions in addition to vessel size are involved in this process.