Cyst

I am 61 years old.  I had a partial hystorectomy about 17 years ago....removal of the uterus only.  Two days ago at my annual checkup, my doctor while pressing the lower sides questioned something she felt on the left side in the ovary area.  She order an ultrasound and the results came back yesterday.  It revealed, according to my doctor, a fluid sack approximately 2 cm on the left side and also looked like fluid in the right fallopian tube.  I am to get an MRI next week.  Of course, the waiting is very stressful.  My question is will the MRI be more thorough than the ultrasound and should I be somewhat relieved that there appears to be no mass.  If it is a cyst, what is the usual process or treatment.  I am not genetically predisposed to cancer.  I am one of 11 children and the only cancer in the family is one brother who had lung cancer.  Also, I know of no ovarian or breast cancer problems in my extended family as well.
Thanks...........belle707