Can it be ignore/does it cause your specific problem?
it might/it might not - depends on size and exact location in relation to your specific anatomy

Is Ultra sound going to help with a cyst compressing a nerve?
no

Are there other reasons that might cause your problem?
yes

Will Ultrasound help with those?
Ultrasound is first and foremost 1 thing - CHEAP! From personal experience i havent seen Ultrasound improving patients situation too often - different dosages and frequency of application do not seem to make any difference in that regard. You can however find an abundance of research on ultrasound many of which claiming that there is indeed some improvement related to the generated heat. Might as well try a warm/hot bath imho.