Can a small area of Juvederm be dissolved or will surrounding filler also get dissolved?

A small amount of hyaluronidase injected into the hyaluronic acid in the overcorrected area typically works locally and should not interact with other injected areas on the face.

Thank you for your question about Juvederm.  Juvederm is a hyaluronic acid based filler (HA), HA is naturally occurring in our joints and skin.  The product stays where it is injected and therefore should not cause harm.  HA fillers are reversible, meaning they can be dissolved.  It is difficult to control hyaluronidase, and may take several sessions.  I recommend following up with your provider to see what he/she recommends.
To be sure you receive the best treatment, see two or more experienced, licensed and board-certified providers in your area for a complete evaluation to make sure you are a good candidate and that it is safe for you to have treatment. I hope this helps

Hyaluronidase works only in the area that you have injected. The product shouldn't migrate to other areas. 

This is a good question. There is no guarantee that the surrounding Juvederm wouldn't dissolve to some extent.  Your physician may try small amounts and add more on subsequent visits if necessary.

Hyaluronidase is a liquid used in very small amounts to dissolve unwanted filler.The injector will be able to dissolve the specific area of concern without affecting the surrounding areas of Juvederm.  This make take a few treatment sessions of small quantities to ensure that the undesired filler is dissolved while preserving the desired filler.

Injecting hyaluronidase to dissolve juvederm will only affect the area where the hyaluronidase was injected.

You can expect the hyaluronidase to migrate approximately 2 cm from the point of injection.  Multiple small volume injections at 1 week intervals would be my approach if you were trying to limit the effects of hyaluronidase to a specific targeted area.
Good luck.