I had a mamogram and then had to have an ultrasound on my left breast. My breasts are dense and they have trouble reading mamograms etc. The result was I have a 4mm hypoechoic nodule. My GP told me they feel it is likely to be a complex cyst. I am to go back for another ultra sound in a year. Please explain what a complex cyst is and how concerned should I be about this. Should I wait a year as advised. Sally