I am assuming that you had a HSG (hysterosalpingogram) because you are having trouble getting pregnant. A HSG is commonly used in working up infertility, especially looking for abnormalities of the uterus that might prevent an egg from implanting or distortions in the fallopian tubes that might prevent the egg from traveling down to the uterus.
In order to get a full interpretation of what the results of your HSG mean in this context, you will need to schedule a visit with the OB GYN doctor
or the fertility doctor
who is helping to work up and treat your condition. They will be able to review the images from the HSG and comment specifically on the dilated fallopian tube.
At first pass, I would say that having a dilation of the fallopian tube is not as bad as having a block fallopian tube, although this does depend on how severe the dilation is. Typically, blockage or dilation of the tube are both caused by the same process, namely scarring and inflammation in the fallopian tube. Therefore, this finding might be related to the underlying problem of infertility.
Make an appointment to discuss these results and potential treatment options with your doctor as soon as possible.