Hysterosalpingography (HSG) involves inserting a contrast medium through the female reproductive tract in order to see it via X-ray scan. When the result is positive, it means that apparently there is no abnormality—the walls of the uterus are uniform, and the tubes have a cord-like structure (filiform aspect).
Conversely, if there is a tubal blockage, the contrast medium will be unable to travel through the tubes and reach the abdominal cavity. In other words, it will not be possible to see the Fallopian tube through X-ray. If the blockage is located in the nearest part of the tube to the ovary, a dilated tube may be seen, as the contrast medium will be stuck inside without flowing in a forward direction.