Dear evev: If this cyst is really 0.3mm, I doubt it cold even be visualized on an ultrasound. More likely this is a 3mm cyst (about 1/8 inch). It would still be too small to aspirate (which is the usual treatment for a cyst if the cyst is causing pain). A cyst is by definition benign. So, if it is a cyst, there is no reason to worry.