Some patients with varicose veins in the lower extremities have poor surgical results and are prone to recurrence, and the culprit is the main character of the topic we are going to talk about today: iliac vein compression syndrome. So how does it happen? And why is it always more likely to occur on the left side than on the right? In fact, it is based on the special anatomical relationship between the left common iliac vein and the right common iliac artery at their respective starting points. The bilateral common iliac veins merge into the inferior vena cava on the right side of the lower middle plane of the fifth lumbar vertebra and travel up the spine, while the right common iliac vein is almost continuous with the inferior vena cava in a straight line, while the left common iliac vein travels transversely from the left side of the pelvis to the right and merges with the inferior vena cava at an almost right angle before passing through the lumbosacral vertebrae. ! The abdominal aorta descends from the left side of the spine and divides into the right and left common iliac arteries in the plane of the inferior border of the fourth vertebra, with the right common iliac artery crossing in front of the left common iliac vein and then extending to the lower right side of the pelvis. In this way the left common iliac vein is more or less pushed forward by the physiological type of anterior convexity of the lumbosacral vertebrae, and at the same time is pressed backward by the right common iliac artery that crosses its front, so to speak, in an anatomical position of anterior compression and posterior crowding in the abdominal back! Iliac vein compression not only causes venous reflux obstruction and lower extremity venous hypertension, becoming one of the causes of lower extremity venous valve insufficiency and superficial varicose veins, but also can be secondary to iliofemoral vein thrombosis, which is also a potentially important reason why venous thrombosis is prevalent in the left lower extremity. It is easily missed by ultrasound due to intestinal gas interference, while interventional angiography can easily identify it! The left common iliac vein merges into the inferior vena cava and widens significantly, and gradually thins distally, giving it a flared shape with thick proximal and thin distal ends; ② the vein in the compressed segment becomes thin or narrow, and the distal external iliac vein is significantly dilated; ③ a limited filling defect, which can be manifested as one or more punctate or block defects; ④ the vein Occlusion is mostly seen in the common iliac vein, and if secondary to thrombosis, it may present as a longer segment of occlusion up to the external iliac vein; ⑤ A large amount of collateral circulation is established. Interventional treatment (balloon dilation, stenting) has also gradually become an important tool in the treatment of iliac vein compression syndrome in recent years, which acts directly on the diseased segment, supporting the venous lumen to avoid compression by arteries and lumbosacral vertebrae, while relieving the stenosis caused by abnormal structures in the lumen by dilating the lumen, and is less invasive and easier to perform, thus showing good prospects for application. Complications are less frequent. The main tissue composition of the abnormal luminal structure of the diseased iliac vein is collagen fibers and fibroblasts, so its physical properties lack elasticity and extensibility, which makes the lumen expansion difficult during the intervention and the expanded wall is very easy to retract, so stenting after balloon expansion is necessary. Since it is often difficult to expand the diseased iliac vein to its normal diameter and excessive tension can lead to wall rupture, the selection of a stent with a slightly larger diameter than the balloon and relatively low tension can make the operation safer without the need to expand the diseased segment to its normal diameter.