When attempting to test for blocked fallopian tubes, an HSG is performed whereby dye is injected into the uterus. If the fallopian tubes are open, the dye will flow through the fallopian tubes at out the ends. Sometimes dye will not flow into the tube(s) because of an obstruction or “spasm” of the muscle around the opening of the tube. With an HSG alone, it is impossible to distinguish an obstruction (which is important) from spasm (which is of no importance). Furthermore, if a true obstruction exists, with an HSG alone, there is no way to bypass it.
With selective salpingography, a smaller diameter, flexible catheter can be run inside the HSG catheter and, with the help of the x-ray machine, can be directed right into the opening of the fallopian tube. Once this is done, dye can be introduced directly into the fallopian tube.
With this technique, it is possible to demonstrate a normal, patent, fallopian tube whose opening may be in spasm. Fallopian tubes with an actual obstruction can also be opened by the higher pressures which can be achieved with selective salpingography.
NOTE: SELECTIVE SALPINGOGRAPHY MAY NOT ALWAYS BE ABLE TO OPEN AN OBSTRUCTED TUBE