Pelvic floor imaging

There are two main types of scan/test for examining the pelvic floor: defaecating proctography (which can be done using xrays or MRI, see below) and endoanal ultrasound.

Defaecating proctogram

This test is used to look at the movement of the back passage (the rectum and anal canal) during defaecation. Many people suffer from problems with being able to open their bowels effectively, and the only way of knowing from the outside what is actually happening during the act of going to the toilet is to do some form of imaging test.

Symptoms that indicate you may need this test include:

  • straining a lot but not being to open bowels easily (obstructed defaecation)

  • a feeling of needing to go again soon after going to the toilet

  • a feeling of a bulge at the front (rectocele)

  • needing to press or push with fingers to help you to go

  • a lump coming out of the back passage when you go to the toilet (prolapse)

Although not as widely discussed in the media as cancer or heart disease, problems with the pelvic floor affect a very large number of people, predominantly women. However, men can also be affected. The symptoms are troubling and impair normal daily life and activities. However, people should be aware that there are many treatments available and although it is an embarrassing problem to face, once you take the brave step of seeing your doctor and having a scan, you are part of the way to solving your problem.

The xray version of the test involves putting some barium paste into the back passage, and this shows up on the xrays. Some barium is also drunk to show the small bowel. The patient is asked to sit on a commode next to the xray machine, while the radiologist and radiographer are behind a screen. Xrays are taken with the patient at rest and straining.

This is what the first xray usually looks like, with the barium paste in the back passage:

The white is the barium paste. The white that can be seen in other bowel loops at the top of the picture is within the small bowel, and during the test I will see if this drops into the pelvis to press on the rectum. This next movie clip (from my YouTube channel) shows what happens during evacuation (i.e. actually going to the toilet) in someone with a rectocele. Note that in normal xrays like the one above, barium is white, and in the movie clips like below, barium is black.

As you can see, the paste comes out of the back passage but some gets trapped in a bulge at the front (to the left side of the picture). This bulge at the front is called a rectocele, and can cause a feeling of a bulge at the front. Stool can become trapped in a rectocele, so people with this sometimes feel like they can't empty their bowels completely. They may need to press with their fingers from the front to help empty their bowels.

Another common reason for doing this test is to test for bowel prolapse. This is when part of the rectum comes out of the back passage, with a feeling of a lump. Although your doctor may be able to see this when they examine you, it is useful to know how big or small a problem it is, and if there are any other problems with pelvic floor. Only a proctogram can give this information.

This next video is another proctogram showing a rectal prolapse:

The barium is evacuated from the back passage and part of the rectum also comes out, meaning there is a "full thickness prolapse". The larger area of black that stays at the end of the test is the barium given as a drink to show the small bowel. In this case, it drops down very low and presses on the rectum. This is called an enterocele.

MRI proctogram

You may have also heard of people having proctograms not using xrays, but MRI. The major advantage of normal xray (also known as fluoroscopic) proctograms is that they are done with the patient sitting down in the same position as they would on the toilet at home. The vast majority of MRI scanners are fixed horizontally, which means that scans can only be done lying down. There are very few "open" MRI scanners in which patients can sit, and certainly not enough to allow this test to be done. Although patients lie down for MRI proctograms, it is not as unusual as it sounds! The legs can be bent at the knees with a soft wedge which helps to be able to open the bowels.

The results of studies that compared a lying down MRI proctogram versus a sitting fluoroscopic proctogram are mixed, but there are a number of advantages of MRI over fluoroscopic proctograms. Ultrasound gel is used instead of barium paste. This is far more pleasant and cleaner. The most important advantage is that as well as giving information about rectoceles, prolapses and enteroceles as above, it gives information about the "anterior" and "middle" compartments. The pelvis is divided into three compartments; the posterior (or back) contains the rectum and anal canal. The anterior (or front) compartment contains the bladder, and the middle compartment contains the vagina and uterus.

When people suffer from problems with the rectum, it is usually as a result of some sort of failure of the "pelvic floor", and the pelvic floor provides important support to all three compartments. Therefore, problems with the bladder such as cystocele, or problems with the vagina and uterus such as uterine prolapse or vaginal prolapse all go hand-in-hand with conditions such as rectoceles and rectal prolapses. For this reason, it is better to call the test a "dynamic pelvic floor MRI".

The only way to evaluate the anterior and middle compartments using fluoroscopic proctograms is to put some xray dye into the bladder (using a catheter) and some barium paste on a swab in the vagina. A far more pleasant method is to use MRI: on MRI, soft tissues are seen much more clearly than on xrays. The urine in the bladder is seen as white so there is no need to put a catheter and xray dye in.

MRI provides a "global pelvic floor assessment": the only thing put in is some ultrasound gel to show the rectum, but we get information about all three compartments. Here is an example of an MRI proctogram showing a small rectocele and a cystocele (which wouldn't be seen on a normal fluoroscopic proctogram):

The reason that this is important is that fixing only a rectocele or rectal prolapse may not relieve all your symptoms. You may also have a cystocele or uterine/vaginal prolapse which become apparent only after having rectal surgery. Knowing exactly which organs are involved in your pelvic floor problem from the outset means that your surgery can be tailored to fix all your problems, and hopefully relieving you of your symptoms.

Endoanal ultrasound

This test is designed to examine the sphincter muscles around the back passage. The machine used is very similar to a normal ultrasound machine that might be used to scan your liver or during pregnancy, but the probe is specially designed to examine the sphincter muscles in detail.

The commonest reason for doing this test is incontinence or stool leakage. The muscles may become damaged during childbirth (if you tear or require a cut or episiotomy), after surgery for anal fistulas or fissures, and following anal trauma. The two muscles examined are the internal and external sphincters. The test is quite quick to perform, it usually takes 2-3 minutes to get all the pictures.

In this image there is a dark C shaped muscle on the left side of the picture, but this muscle should actually form a complete ring. This means that there is a tear of the internal sphincter muscle.

Note that endoanal ultrasound is only a part of sphincter muscle assessment. The scan doesn't tell us anything about how the muscles actually work. A separate test needs to be performed for this, called endoanal physiology, which shows how well the muscles can squeeze.