I have added some pictures to help with the discussion. Take your time with them, if you are not used to looking at medical drawings or photos it takes a little while to get your bearings.The first picture is a drawing of a normal uterus, no septum, not bicornuate. You can see the top of the uterus is slightly rounded, not indented. The inside is shaped like a triangle. The space inside the uterus is called the uterine cavity. The pink tissue surrounding the cavity is the myometrium, which is the muscle. This picture also shows the tubes and ovaries off to each side.
The next picture is a drawing of a bicornuate uterus. It has a portion to the left and a portion to the right. The uterine cavity is not triangular, it is Y shaped. The top middle of the uterus is indented in.
The next picture is a drawing of a septate uterus. (The pictures on this post come from different sources so the drawing style may be a little different). Here, the uterine cavity is Y shaped, just like the bicornuate. The top of the uterus is not indented, it is slightly rounded. Basically, the uterus looks normal on the outside, but has a septum on the inside.
So both have a Y shaped uterine cavity. A hysterogram only shows the uterine cavity. The x-ray dye goes into the cavity and then out the tubes. So a bicornuate uterus and a uterus with a septum can look the same on hysterogram. Other tests are necessary to tell the difference. If your only test has been a hysterogram and you were told you have a bicornuate uterus, you need more tests.
Even more tests may get you the wrong answer. Radiologists are notorious for calling a septate uterus a bicornuate uterus. I don’t know why. Maybe they don’t understand the difference, or they know there is a difference but are not aware that the treatment options (next blog) are different. Even if a special test is ordered, such as an MRI or a 3-d sonohysterogram, the incorrect terminology gets used.