Preprocedure Preparation

As with any procedure, it is extremely important to obtain a history of the patient’s symptoms. Specific questions may have to be asked, such as the use of any maneuvers that may assist the patient. This is not always volunteered because the patient may be too embarrassed to disclose them. Also, this is very intrusive, so the examination must be thoroughly explained prior to anything being done. This ensures that the patient understands the instructions given during the procedure. Getting the patient to practice some of the maneuvers, such as squeezing the buttocks while sitting on the side of a stretcher prior to instillation of any contrast, is also useful. The patient should have maximum privacy and be comfortable as possible in the examination room. One way to achieve this is to use a remote control fluoroscopy unit, turning the lights down low and ensuring that the patient is the only person in the examination room. In our unit, we also have blinds so that the patient cannot see the radiologist operating the remote fluoroscopy unit. Generally, if the patient is comfortable with the environment, the greater the likelihood of an accurate assessment of defecation.

Imaging Technique

Imaging of defecation was described as early as the 1950s. It was not until the 1980s that Mahieu and colleagues described a technique that interested more radiologists. This technique has since been further modified with the addition of opacification of the small bowel, urinary bladder, and vagina. The opacification of these structures makes recognition of cystoceles, enteroceles, and sigmoidoceles easier. Preparation of the bowel with laxatives or enemas is not necessary, although some authors believe that a limited bowel preparation will be more comfortable for the patient and also provide a more standardized examination. The order of opacification is to give oral contrast first to opacify the small bowel. Usually, about 400 mL of contrast used for small bowel studies is sufficient. This is given about 45 to 60 minutes before the dynamic part of the examination. Some authors suggest waiting for up to 3 hours. How long you have to wait depends on how long it takes for the small bowel contrast being used to opacify the pelvic loops of the small bowel.

Opacification of the urinary bladder is next, with water-soluble contrast normally used for cystography. About 150 to 200 mL of contrast is enough to make the bladder recognizable. Care must be taken not to overdistend or it could mask enteroceles. Overdistention is also uncomfortable for the patient.

The vagina is then opacified. This can be done with barium paste, high-density barium, or a thick solution of 50% contraceptive gel and 50% of water-soluble contrast with the highest concentration of iodide. The vaginal contrast is introduced with a bladder irrigation syringe connected to a soft catheter. A pediatric enema catheter works well. The catheter is inserted deep into the vagina and the contrast introduced as the syringe is slowly withdrawn. Care must be taken to ensure that there is sufficient contrast opacifying the whole vagina. In the past, a contrast-soaked tampon was used. However, it was noted that the tampon acted as a strut and did not allow any enteroceles, rectoceles, or sigmoidoceles to become apparent.

Finally, the rectum has to be opacified. It helps to have contrast material that has the consistency of stool or at least close to it. If it is too liquid, even normal patients will find it difficult to hold in the rectum. Currently, there are no commercially made preparations available. The options are to use a thick esophageal paste such as Esobar (Bracco Diagnostics Inc., Monroe Township, New Jersey) or the thick paste, as suggested by Mahieu and associates. Three 50-mL syringes (150 mL total) of Esobar introduced into the rectum are usually enough to perform the procedure. When the syringes are filled, care should be taken to eliminate air bubbles because trapped air under pressure can cause discomfort to the patient ( Fig. 52-3 ). The syringes are easier to fill if the paste is first warmed by holding the contrast tube under hot water. If the Mahieu preparation is used, it is useful to opacify the rectal wall first with contrast used for barium enemas. The doughy paste, if prepared as suggested, provides bulk but does not opacify the wall. Therefore, intussusceptions could be missed. The other disadvantage is that because of the consistency, it is difficult to introduce into the rectum. An orthopedic glue gun that is geared makes this thicker paste easier to introduce. To coat the rectal wall and fill the rectum with the Mahieu paste, attach a 50-cm length of 0.5-inch tube filled with high-density liquid barium to the glue gun, with a wide-bore enema tip at the end, so that both contrast agents can be introduced in one maneuver. The rectum is filled until the patient reports a sensation of fullness and a desire to defecate.

Supplies used during the examination.

A. Syringe with a pediatric enema tip for the vaginal contrast, Esobar for the rectum, petroleum jelly with Vaseline as an anal marker, and lubricant. B. Other supplies that may also be used include a caulking gun to introduce contrast, contraceptive jelly with contrast for vaginal opacification, and commercially prepared rectal contrast. C. If the barium is not used for vaginal contrast, contraceptive jelly mixed with water-soluble contrast with the highest iodine content is used with a bladder irrigation syringe and pediatric enema tip.

Finally, if you wish to measure the anal canal or determine the location of the anus, the surface around the anus should be opacified. This can be done with petroleum jelly opacified with barium. Petroleum jelly, 50 g, with 50 g of barium works well. This is smeared around the anus and along the natal cleft.

When the patient is ready for the study after all the contrast has been introduced, the patient is asked to sit on the defecography commode. The commode design should allow filming in lateral and frontal projections. A sturdy commode also dispels any fears that the patient may have about sitting on it. There are commercially available commodes but you can build one to your own design. A commode designed by Bernier and colleagues has a ruler in the midline so that direct measurements of the midline structures can be done if necessary. If a remote control fluoroscopy unit is used, the commode can be attached to the table top ( Fig. 52-4 ). Positional changes of the commode can then be easily made by moving the tabletop. A remote control fluoroscopy unit is certainly preferable for this study.

Defecography commode.

A. The commode for the procedure is attached to a remote fluoroscopy table so that the patient can be positioned using the tabletop movement. These steps make it easier for the patient to get to the seat. B. The dish in the commode has a radiopaque ruler (in centimeters) so that direct measurements can be made from the images. The dish is also covered with a plastic bag so that after each patient, all that needs to be done is to replace the bag. R, ruler.

The x-ray beam is aimed at the region of the reproductive organs. Therefore, keeping the radiation dose as low as possible is paramount. To keep the dose low, several investigators use only videofluoroscopy. Although the dose is low, the resolution is not adequate to record subtle radiographic changes. Therefore, it is recommended that videofluoroscopy be performed during the entire examination, with spot films being taken at key events. The key spot images are lateral views of the rectum at rest, lift (squeeze), cough, strain, defecation, and postdefecation. Other ways of reducing radiation dose include digital serial acquisition with one image/s for 30 seconds or using digital equipment with a low-dose program. Major reductions in radiation dose can also be achieved by slow pulsed fluoroscopy. Additional beam filtration can reduce radiation without impairing image quality.

The images at rest are taken without any conscious contraction of the pelvic muscles ( Fig. 52-5A ). On lifting (squeezing), there is maximal contraction of the pelvic floor musculature. This results in elevation of the entire pelvic floor (see Fig. 52-5B ). The muscles responsible for elevation of the pelvic floor are the puborectalis and levator ani. The anorectal angle becomes acute with maximum elevation. The squeeze image demonstrates pelvic floor strength, and impaired movement may reflect puborectalis atrophy. The anal canal simultaneously lengthens. These changes can be measured and are indicators of the continence mechanism. When asked to cough, the patient should produce a powerful cough in the rest position. This action simultaneously increases intra-abdominal pressure and contraction of the anal and pelvic floor muscles. In normal individuals, there is minimal or no descent of the pelvic floor and total continence (see Fig. 52-5C ). When asked to strain, the patient should strain downward maximally, without evacuating (see Fig. 52-5D ). This maneuver stresses the continence mechanism and provides a measure of pelvic floor descent. The anal canal shortens during straining in most women (mean change, 2 mm). Almost all patients demonstrate some perineal descent, but this is the least reliable portion of the examination because some patients paradoxically contract the pelvic floor muscles, perhaps for fear of incontinence. Straining is supposed to demonstrate the competence of the external anal sphincter.

Normal examination.

A. Normal, at rest. The vagina (V) has a close relationship to the anterior wall of the rectum (R). The small bowel (SB) has been opacified. B. Normal with lift (squeeze). The anorectal junction is above the level of the ischial tuberosities and there is good contraction of the puborectalis (PR). C. Normal, with coughing. There is virtual no movement of the anorectal junction (ARJ). The bladder (B) and vagina (V) have been opacified. D. Normal, with straining (S). Again, the ARJ maintains a normal position and there is no incontinence. E. Normal beginning of defecation. The anal canal is open and there is good emptying. At the end, the rectum is almost totally empty, with some stray contrast remaining.

Finally, spot films are obtained during defecation and postdefecation straining (see Fig. 52-5E ). These films give a measurement of pelvic floor descent and an estimate of the completeness of emptying. Morphologic abnormalities such as intussusception and rectoceles are often visualized at this time, and the changes contributing to difficulty in defecation can be analyzed. Rectoceles are outpouchings of the rectum beyond the expected contour of the rectal wall ( Fig. 52-6 ). They are often normal and are more common in women. If a rectocele does not empty completely during defecation, it may produce a feeling of incomplete evacuation of the rectum.

Rectocele (R).

This is normal, except when it does not empty at the end of defecation. SB, small bowel; V, vagina.

Anorectal Angle

The anorectal angle ( Fig. 52-7 ) is measured between the axis of the anal canal and the tangent to the posterior wall of the rectum. It can be difficult to measure because the posterior wall of the rectum is often not clearly delineated, and the angle becomes highly subjective. Caution should therefore be exercised when assessing its significance. At rest, this angle is usually no greater than 120 degrees in control subjects. However, the angle has a normal range of 70 to 134 degrees, with a mean of about 95 degrees. When the patient squeezes or lifts the buttocks, the anorectal angle decreases to a mean of 19 degrees in women (range, 6 to 26 degrees) and a mean of 28 degrees in men (range, 12 to 45 degrees). This angle increases during straining and defecation. The mean anorectal angle during straining in normal young women is 103 degrees, with a range of 75 to 108 degrees. In men, the mean angle is slightly lower, 98 degrees, with a range of 67 to 123 degrees.

Schematic showing the anorectal angle.

The lines AB and CD subtend the posterior anorectal angle. The position of AB is easily determined; CD can be much more difficult to draw. The thicker line shows the position of the anorectal junction. Below it are the two parallel lines that form the anal canal. The thinner lines point to the puborectalis impression.

Anal Canal Length

The anal canal length is easily measured. It is the distance traversed by the parallel borders of the anal canal before they form the diverging walls of the distal rectum. At rest, the mean length of the anal canal is 16 mm in women (range, 6 to 26 mm) and 22 mm in men (range, 10 to 38 mm). During lifting (squeezing), the anal canal lengthens to a mean of 19 mm in women (range, 9 to 26 mm) and 28 mm in men (range, 12 to 45 mm). During straining, the canal shortens slightly and has a mean length of 14 mm in young women (range, 6 to 20 mm) and 17 mm in young men (range, 9 to 27 mm).

Level of Anorectal Junction

The anorectal junction is the uppermost point of the anal canal. Its position is measured from an easily visualized fixed point, the ischial tuberosity. A positive value indicates a position above the ischial tuberosity, whereas a negative value indicates a position below it. In normal young men at rest, the mean level of the anorectal junction is 16 mm and increases to 28 mm during lifting (squeezing). It drops to −4 mm during defecation. In young women, the mean values for the same maneuvers are 4 mm at rest, 14 mm during lifting (squeezing), and 16 mm during defecation, measurements significantly different from those of normal young men.

Although these measurements can be made, in routine practice it is not done because of the poor reproducibility, especially the anorectal angle and descent of the anorectal junction. Occasionally, unusual or unexplained findings are seen on lateral views, and anteroposterior or oblique views are needed for further clarification. Some patients have a history of using a variety of maneuvers to facilitate evacuation. These patients should be encouraged to use these maneuvers during the examination, and the mechanisms aiding evacuation should be identified. When patients have a large anterior rectocele that remains full even after the rectum has completely emptied, they may complain of incomplete emptying. These patients typically empty the rectocele back into the rectum by digital perineal or vaginal pressure. In patients with a history of obstructed defecation, it is sometimes helpful to perform the examination first with liquid barium, which makes expulsion easier. If this approach is successful, the examination should be repeated in the usual way with one of the thick barium pastes.