What's one of the worst scenarios for WEB embolization? It's migration! 

Web is one of the safest devices on the market, simple to use and very efficient.
When you use a coil, there is a risk for it to migrate out of the aneurysm, it’s the same risk when you use a web device. The risk now is to deal with those migrations.

How to prevent the migration of your device:

• The risk is higher using the 17 system and small web sizes for small aneurysms.
• Sizing is very important, there is a tendency to undersize the device which will determine loose wall apposition and a risk of distal migration.
• The risk is higher in high-flow situations T-basilar / T-carotid and the risk if higher if forceful contrast injections are being made immediately after deploying in these positions.
• Always use simulation to be able to see that your device is not undersized and that it will have good wall apposition. 
• Ensure that you push your devices inside the sac, do not detach the device unless you are sure that it is well apposed in the aneurysmal sac. Vaso-CT before detachment may clarify it.

In the following cases, the web devices have been moved from their original location. We are using two differents devices to try to get them.

How to remove a distally migrated WEB-device:

• When you are dealing with any complication, remember to the first point is not to make the matter worse!
• Ensure you switch your system to a tri-axial one:
  1. Ideally use a 6-FR distal access catheter (you need good navigability and proper internal lumen);
  2. 5-Fr distal access catheter may be enough (but you take the risk of not being able to ingest the WEB);

• Try to pass the WEB with a 0.21 microcatheter on a 0.14 guidewire, use gentle torquing movements, you should be able to pass between the WEB and the wall of the artery. If you feel passing with a guidewire is to dangerous you can also pass with the empty catheter. Once you pass the WEB there are two options:
  1. Deploy a stent-retriever (like Solitaire 4x40);
  2. Deploy a micro snare through the 0.21 microcatheter and catch the WEB in a distal to proximal fashion.
     
     
• Once you catch the WEB with either approach, you should advance your distal access catheter to the WEB and try to pin it between your micro snare/stent-retriever and the distal access catheter. Try to ingest it if possible, if not perform a WEB-ectomy manoeuvre while pulling everything.
• If passing with a 0.21 microcatheter is not working, it is possible to pass with a 0.17 microcatheter and use a 0.17 compatible stent-retriever (ex. Tiger6retriever), with this technique you will be able to control the actual level of inflation of your stent during the retrievel maneuver inside the aspiration device.
• Theoretically the WEB is a compressible device, if you are not able to retrieve it – the last resort option would be to stent it to the vessel wall. Ideally, deploy a Solitaire AB and perform a vasoCT. If you think that the result is acceptable and the WEB is compressed you may detach. 

In the bloc B, the doctor Vitor Mendes Pereira (Toronto, Canada) is using a tigertriever 17 by Rapidmedical