Empty pockets in lips after dissolving and refilling - can these ever be fixed? It has been 4 years since my initial filler.

Unfortunately, it is difficult to give you any feedback without at least a photo or two. In most cases, lip fillers will not cause hollowing in the lip area since the skin will usually conform well around the new lip shape.I encourage you to schedule a second opinion with another board-certified dermatologist if you are not completely satisfied with your initial treatment. Through an in-person assessment and discussion of your concerns and goals, your doctor should be able to recommend a treatment plan for you if appropriate. 

Thank you for sharing your excellent question.  Unfortunately without a series of photographs it is difficult to offer definite advice. I would recommend reposting images for the best advice. 

Dear fubybb,
I perform a lot of lip injections with fillers such as juvederm and it works great. Many times I need to put more in one side than the other to attempt to even out the vermillion border (The red line of the lip). This helps provide more symmetry at times.
Another Option: For patients looking for a more long lasting result, I recommend fat grafting. That is, using your own bodies fat to make your lips naturally look more shapely. The bonus is that the results last many many years.
In general, I avoid using permanent prosthesis because I find that the lips are such dynamic and sensitive structures, the end result is not natural.
Daniel Barrett, MD