Any cyst needs a specific surgical protocol. It will not be cured with medication. Your mother first needs a CT neck to find out where exactly it is, how big it is and how to remove it. Secondly, it may need a biopsy called FNAC, if the cyst can be seen through the mouth An ENT surgeon can do it with the help of a pathologist. Please visit a hospital and consult an ENT department. There is nothing to worry.