Dislocation or escape of the dislodged spring coil is one of the more problematic complications during interventional embolization of aneurysms. The so-called spring coil migration or escape means that the original spring coil that has dislodged in the aneurysm cavity is shifted or escaped into the normal artery by the impact of the blood flow or the pushing of the subsequent spring coils, which will cause cerebral infarction in the area supplied by the artery if the blood flow of the artery is blocked. So, how to prevent the spring coil from shifting or escaping? For “large lumen, small mouth” aneurysms, which we call narrow neck aneurysms, the spring coils do not easily escape from the lumen and we simply embolize the lumen with a microcatheter; however, for “small lumen, large mouth” aneurysms, which we call wide neck aneurysms, an adjunctive tool must be applied to ensure that the spring coils are not displaced or escaped. However, in the case of “small and large” aneurysms, we call them wide-necked aneurysms, it is necessary to apply adjuncts to ensure that the spring coil stays in the lumen. These aids include balloons and stents. Let’s start with the balloon. The blocking balloon system is placed at the aneurysm opening and a microcatheter is inserted into the aneurysm lumen (as shown in Figure 9). The balloon is filled with contrast agent to close the aneurysm opening, and a spring coil is fed through the microcatheter to fill the aneurysm lumen and empty the balloon; if the spring coil is stable, it is released; if the spring coil is unstable and drifting, its position is adjusted or replaced with a larger diameter spring coil until it is stable and then released. Repeat the process of filling subsequent spring coils until the aneurysm is satisfactorily filled. Finally the balloon system is withdrawn and not left in the body. Again, the stent is used. The stent is actually a wire braided tube that can be borrowed from a special delivery system to be delivered into the blood vessel, where it fits snugly against the inner wall of the vessel. The same applies to wide carotid aneurysms. Stent-assisted spring coil embolization can be performed in two ways. The first is called sequential, in which the stent is released at the opening of the aneurysm, and then a microcatheter is inserted through the mesh of the stent into the lumen of the aneurysm to deliver a spring coil to embolize the aneurysm. Figure 11 Stent-assisted spring coil embolization of aneurysm Procedure 1: Sequential type The second type is called parallel type, i.e., the stent delivery catheter and microcatheter are placed in parallel, and the stent is released across the neck of the aneurysm via the stent catheter to press down on the microcatheter pre-positioned inside the aneurysm lumen, and then a spring coil is delivered to embolize the aneurysm lumen through the microcatheter. Figure 12 Stent-assisted spring coil embolization of aneurysm Procedure 2: Parallel approach The end result of both procedures is to leave the stent in the aneurysm-carrying artery for the rest of its life, with the stent acting as a cage to shield the spring coil from the aneurysm cavity and to ensure blood flow to the aneurysm-carrying artery while occluding the aneurysm. Because the sequential technique requires the microcatheter to pass through the mesh of the stent to enter the aneurysm, which makes it more difficult to maneuver, the parallel technique is more commonly used in clinical practice. The difference between a stent and a balloon is that a stent stays in the body permanently, just like a spring coil, whereas a balloon is withdrawn once it has completed its task. So, when to use a balloon and when to use a stent? Simply put, balloons are used for wide necks and stents are used for even wider necks. To be more specific, cylindrical aneurysms with a similar width of aneurysm and neck can be embolized with the aid of a balloon, and of course stents can be used to assist in the embolization of the aneurysm, but conical aneurysms with necks larger than the width of the aneurysm, or pike shaped or laminated aneurysms must be assisted with a stent. Studies have shown that stents are beneficial to reduce the long-term recurrence rate of aneurysms due to their vascular shaping and blood flow guiding effects, so currently stent-assisted aneurysm interventional therapy is more and more widely used, and from the materialistic point of view of various manufacturers have produced a variety of stents with different physical properties, different ways of liberation, and different indications for the interventionalists’ clinical selection. Of course, even with the assistance of balloon and stent, spring coil escape still occurs occasionally, which is mostly seen when the small spring coil that finally fills the neck of the tumor is washed away by the blood flow after the removal of the balloon protection or leaks out of the mesh of the stent and becomes a “fish in the net”. If the spring coil is far away in an unimportant branch distal to the aneurysm-carrying artery, it can be left alone. If the spring coil blocks an important branch, there is no need to be nervous, as we have a special fishing device to fish it out. The colorful interventional materials are like 18 kinds of weapons, which ensure that our endovascular operation is easy to use and win the battle against the enemy.