Video Clips on DVD
- 2-1
Local Examination to Evaluate the Perineum and Anal Sphincters
- 2-2
Endoanal Ultrasound for Evaluation of Anal Sphincter Muscles
- 2-3
Normal Defecography Demonstrating Landmark Features and Anatomy
- 2-4
Defecography Demonstrating a Rectocele and Enterocele
- 2-5
Dynamic MRI Demonstrating Pelvic Floor Descent
Introduction
Patients with complex anorectal functional problems are an inherent part of any medical practice. The presenting symptoms and clinical evaluation may give some indication of the underlying anorectal disorder. However in a number of cases, particularly those in whom one is contemplating surgery, functional evaluation and imaging modalities are adjunctive to history and physical examination. Many tertiary centers dealing with complex anorectal disorders will have a dedicated functional pelvic unit with personnel who have experience in the administration and interpretation of these tests.
Anal Physiology
The pelvic floor is traditionally divided into three compartments: anterior, middle, and posterior. Patients with a problem in one compartment often have a coexisting problem in a second compartment, necessitating a multidisciplinary approach. Bowel control depends on intact functioning sphincters, an adequate reservoir, and consistency of stool. A breech of any of these components may lead to fecal incontinence or outlet obstruction constipation. The rectum itself is a capacious organ with the ability to store large volumes and defer defecation until desired. Its compliance may be lost in patients with ulcerative colitis, after rectal surgery, or with the development of fibrosis secondary to radiation proctitis. Leakage of stool may also occur as a result of poor rectal emptying. Reservoir capacity is also lost in patients with fecal impaction because of limited space for subsequent stool. These patients may develop incontinence in part from overflow and in part because of a chronically relaxed internal anal sphincter (IAS) secondary to continuous rectal distention.
Before defecation, rectal distention with stool stimulates stretch reflexes in the rectum and activation of the rectoanal inhibitory reflex (RAIR). In normal circumstances this leads to a decrease in the resting IAS pressure and contraction of the external anal sphincter (EAS), allowing one to defer defecation until a socially acceptable time. The ability to discriminate gas from liquid and solid stool is known as the sampling mechanism and requires the integration of complex neurologic and enteric processes. At the time of defecation, straining increases the intra-abdominal and intrarectal pressures, which stimulates complete relaxation of the IAS, EAS, and puborectalis, resulting in a straightening of the anorectal angle and defecation. Following evacuation, the pelvic floor and anal canal muscles return to their baseline.
Anal Physiology
The pelvic floor is traditionally divided into three compartments: anterior, middle, and posterior. Patients with a problem in one compartment often have a coexisting problem in a second compartment, necessitating a multidisciplinary approach. Bowel control depends on intact functioning sphincters, an adequate reservoir, and consistency of stool. A breech of any of these components may lead to fecal incontinence or outlet obstruction constipation. The rectum itself is a capacious organ with the ability to store large volumes and defer defecation until desired. Its compliance may be lost in patients with ulcerative colitis, after rectal surgery, or with the development of fibrosis secondary to radiation proctitis. Leakage of stool may also occur as a result of poor rectal emptying. Reservoir capacity is also lost in patients with fecal impaction because of limited space for subsequent stool. These patients may develop incontinence in part from overflow and in part because of a chronically relaxed internal anal sphincter (IAS) secondary to continuous rectal distention.
Before defecation, rectal distention with stool stimulates stretch reflexes in the rectum and activation of the rectoanal inhibitory reflex (RAIR). In normal circumstances this leads to a decrease in the resting IAS pressure and contraction of the external anal sphincter (EAS), allowing one to defer defecation until a socially acceptable time. The ability to discriminate gas from liquid and solid stool is known as the sampling mechanism and requires the integration of complex neurologic and enteric processes. At the time of defecation, straining increases the intra-abdominal and intrarectal pressures, which stimulates complete relaxation of the IAS, EAS, and puborectalis, resulting in a straightening of the anorectal angle and defecation. Following evacuation, the pelvic floor and anal canal muscles return to their baseline.
Patient Assessment
Following a careful history, the perineum, vagina, anal canal, and rectum are examined in a stepwise manner. The perineum is examined for any defects, excoriation, dermatitis, external fistula openings, and so forth. Stimulating the skin around the anus using a cotton swab results in a reflex contraction of the EAS known as the anal wink reflex. Hemorrhoids, fissures, strictures, and keyhole deformities that may occur following previous anorectal surgery are noted on perianal examination. The patient is asked to strain (Valsalva maneuver) to determine if there is any perineal descent, uterine prolapse, or associated rectal prolapse. Full-thickness rectal prolapse, procidentia, is differentiated from mucosal prolapse by visualization of circumferential layers of the rectal wall ( Fig. 2-1A and B ). If rectal prolapse is suspected but is difficult to visualize, the patient is asked to strain on a commode to elicit the prolapse. The external vaginal and perineal area is inspected for scars that may arise following a prior episiotomy or repair of vaginal tears. A pelvic examination is performed, looking for anterior and posterior vaginal support and signs of apical prolapse. Digital rectal examination (DRE) helps to determine the resting and squeeze pressures of the anal canal and relaxation of the pelvic floor muscles. The inability to relax the pelvic floor muscles is known as nonrelaxing puborectalis . A rectocele is diagnosed by vaginal and rectal examination. Proctoscopy in addition to rigid or flexible sigmoidoscopy are performed to assess the rectal mucosa and to exclude low anorectal pathology including inflammatory conditions or cancers. Internal rectal prolapse can be visualized as excessive intrarectal redundancy on proctoscopy but is typically only diagnosed with defecography. (See Video 2-1 for a demonstration of local examination to evaluate the perineum and anal sphincters. 
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Anal Manometry
Anal manometry gives a quantitative assessment of the anal sphincter complex, providing data on anal sphincter pressures, functional sphincter length, anorectal sensation, compliance, and RAIR. It is performed in the office setting using a specially designed pressure-sensing catheter or balloon that is inserted into the anal canal and lower rectum. As the device is pulled out, anal canal pressures are measured at 1-cm intervals, first in the resting state and then following voluntary contraction of the sphincter complex. There are many different commercially available systems. The water-perfused system is relatively inexpensive and well tolerated by patients. Pressures recorded result from the resistance to the flow of water that is perfusing at a known rate through a series of openings on the catheter. There are open-ended or side-open catheters, with up to eight channels used, but four channels are generally adequate. These fluid-filled systems may be prone to artifact particularly related to gas bubbles mixing with the fluid. The leakage of water over the buttocks may lead to voluntary contraction of the anal sphincters and gluteal muscles, giving an aberrant result. Solid-state catheters with microtransducers ( Fig. 2-2 ) are thought to be most accurate.
Technique
The test is performed in a comfortable environment with minimal personnel involved. The patient is placed in the left lateral position. In constipated patients, we advise giving an enema before assessment. The equipment is calibrated, lubricated, and inserted to the 6-cm mark. The length of the high-pressure zone as determined by a continuous pull-through technique may vary between 2.5 and 5 cm, and is naturally shorter in women than men. The maximal resting pressure is the highest resting pressure in the resting state in the high-pressure zone. The maximum squeeze pressure is the highest pressure achieved during squeeze in the high-pressure zone. The mean resting pressure is the mean of all resting pressures recorded in the high-pressure zone. The mean squeeze pressure is the mean of all squeeze pressures calculated in the high-pressure zone. Squeeze pressures reduce as patients get older with the greatest decrease occurring in women. These values vary depending on technique. Normal values need to be decided on at each physiology unit. We define average resting pressure as being normal if greater than 40 mm Hg and average squeeze pressures as normal if greater than 100 mm Hg ( Fig. 2-3 ). Longitudinal and radial variations do occur. In the upper anal canal, pressures recorded for the posterior portion will be higher than the anterior segment, which is attributed to the effects of the puborectalis. In the mid-anal canal the pressures are more equally distributed, and in the lower anal canal the pressures are highest anteriorly.
The rectoanal inhibitory reflex (RAIR) is defined as “the transient decrease in the resting anal pressure ≥25% of basal pressure in response to rapid inflation of a rectal balloon with subsequent return to baseline.” It is elicited by inflating the intrarectal balloon located at the end of the microtransducer catheter with 10 to 30 mL of air and observing the change in resting canal pressures from baseline. The RAIR relies on an intact neuronal plexus and is absent in patients with Hirschsprung and Chagas diseases. It has also been demonstrated to be absent after a low anterior resection, coloanal anastomosis, or ileal pouch anal anastomosis.
Rectal sensation can be measured with balloon distention or the barostat. The first sensation is typically elicited following 10 to 20 mL of air. As more air is introduced, the rectum distends, and the patient reports the urge to defecate and the maximum tolerable volume. Rectal compliance is calculated and reflects the ability of the rectum to accommodate to different volumes without altering rectal pressures. Low rectal compliance occurs in patients with inflammatory conditions of the rectum, and increased compliance has been observed in patients with diabetes, fecal impaction, and megarectum.
The rectal balloon expulsion test is an inexpensive method to assess the rectal evacuatory function. A latex balloon is inserted into the rectum and filled with air or fluid. This test can be performed in the sitting or supine position. This balloon is inflated to 50 mL, which the patient is then asked to extrude. If this is unsuccessful then the balloon is inflated to 100 mL. Failure to expel the balloon within 60 seconds suggests a pelvic floor problem.
Anal Endosonography
Endoanal ultrasound (EAUS) is an excellent modality to provide information on the integrity of the sphincter complex. This test is very well tolerated by patients, and in experienced hands it has a very high sensitivity for detecting defects in the IAS and the EAS. This is particularly important in patients with fecal incontinence in whom one suspects a breach in the sphincter that may be amenable to surgical repair.
Technique
A 360-degree rotating transducer allows circumferential assessment of the anal canal. It comes with a 7- and 10-megahertz (MHz) probe for the two-dimensional (2D) units and 13 MHz for the three-dimensional (3D) equipment ( Figs. 2-4 and 2-5 ). The 10-MHz frequency crystal gives a focal length of 1 to 4 cm, which is ideal for sphincter assessment. The patient receives a pretest enema. It is important to ensure there is no coexisting pathology such as an anal fissure or stenosis that would make probe insertion painful or difficult. The test is performed with the patient placed in the left lateral position. A hard cap that makes contact with the anal canal is useful for sphincter assessment whereas an inflatable balloon is needed to assess patients with a very patulous anus or for rectal tumors above the anal sphincters. Following careful insertion of the probe, images of the upper, middle, and distal anal canal are recorded. In the upper anal canal the landmark structure is the U -shaped puborectalis. The puborectalis is visualized as a white hyperechoic structure secondary to the skeletal muscle. This blends into the EAS in the mid-anal canal. In contrast, the internal anal sphincter is made up of smooth muscle, which is seen as a dark hypoechoic band on the ultrasound because of its large water content. It is maximally thickened in the mid-anal canal. In the mid-anal canal both the IAS and the EAS should form a complete ring ( Fig. 2-6 ). Anal sphincter injuries are characterized by a break in the muscular ring. A finger may be inserted on the vaginal introitus, the imprint of which can be seen on ultrasound, giving anterior orientation ( Fig. 2-7 ). A perineal body measurement is taken from the tip of the finger at the vaginal introitus through the thickness of the IAS. Normal perineal body measurements are 12 mm, and values less then 10 mm are suggestive of sphincter injury. In the lower anal canal, the EAS only is seen, which represents the subcutaneous component of the muscle.
Two-dimensional (2D) images are obtained at the upper, middle, and distal canal and the images are labeled. When 3D views are taken, following data acquisition, the scans may be reconstituted in different planes ( Fig. 2-8 ). This is particularly useful in examining the anterior part of the external anal sphincter looking for defects. (See Video 2-2 for a demonstration of endoanal ultrasound for evaluation of anal sphincter muscles. 
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Cinedefecography
Cinedefecography was first introduced in the 1960s and is a dynamic study that requires opacification of the pelvic floor structures with contrast and simulation of evacuation. It is performed on patients who have difficult evacuation or selectively on patients who have fecal incontinence when rectal prolapse is suspected. This study is performed in the fluoroscopy suite with the aid of video recording and freeze-framing to measure the anorectal angle, perineal descent, and the size of a rectocele. This test is very useful in identifying mechanical etiologies of obstructed defecation such as rectocele ( Fig. 2-9A and B ), enterocele, sigmoidocele, internal intussusception, and rectal prolapse. Functional etiologies such as nonrelaxing puborectalis and a capacious rectum, megarectum, may also be seen. Cinedefecography is also useful in patients with documented slow-transit constipation to ensure there are no evacuatory problems before considering a subtotal colectomy with ileorectal anastomosis. This test should be avoided in pregnant female patients, and care should be taken to limit the extent of radiation exposure. The number of personnel involved in the test must be kept to a minimum, and the environment must be suitable to allow patients to comfortably defecate, replicating their normal pattern. Critics of this test feel that the attempts to visualize what happens at defecation in a laboratory environment are flawed.
Technique
The technique used may vary between centers and may be adjusted depending on the associated pathology that one is trying to elucidate. In our center a gentle bowel preparation is given before the procedure. The patient takes oral barium 1 to 2 hours before the defecating proctogram to highlight the small bowel and allow the identification of an enterocele. We use a catheter to fill the vagina with contrast, although others prefer to insert a contrast-soaked tampon. A rectal catheter is used to instill liquid barium into the sigmoid colon followed by viscous barium paste into the rectum to replicate stool. Barium is continually instilled until the patient experiences a feeling of rectal fullness and a strong urge to defecate or to a maximum of 200 mL (500 g) of paste.
More invasive techniques have been reported, such as opacification of the bladder to aid in the diagnosis of cystocele and enhancement of the peritoneum, peritoneography to improve visualization of the pelvic floor structures and to diagnose peritoneocele, a peritoneum-lined sac that herniates between the vagina and rectum. It may be filled with any intra-abdominal structure including the omentum and small bowel. Peritoneography carries an additional risk of infection because of instrumentation and is only selectively performed at specialized centers. Following the administration of contrast, the patient then sits on a radiolucent commode, and the fluoroscopy is performed in a lateral view. The patient is initially asked to relax, squeeze (contract the pelvic floor muscles), and then strain (push down without evacuation). Still images are taken, and descent can be measured after the study is completed. The patient is then requested to defecate the rectal contrast, and the resulting fluoroscopic images are video-recorded. If evacuation is prolonged, then care must be taken to limit the extent of radiation exposure.
Interpretation of Results
The following findings are noted on the defecography report: delayed or incomplete rectal emptying, changes in the anorectal angle, anterior or posterior rectocele, sigmoid or small bowel descent below the pubococcygeal line (sigmoidocele or enterocele [ Fig. 2-10 ], respectively), perineal descent, internal intussusception, and full-thickness rectal prolapse. The lines of reference are the pubococcygeal line from the inferior border of the symphysis pubis to the last joint of the coccyx and the ischiococcygeal line from the tip of the ischium to the coccyx. Descent of the sigmoid or small bowel is recorded as grades I through III. Grade I is below the pubococcygeal line (and above the ischiococcygeal line). Grade II is below the ischiococcygeal line, and grade III refers to maximal descent along the perineum. Reference lines are also drawn along the axis of the mid-anal canal and the posterior rectal wall. A rectocele is defined as an outward bulge of the rectal wall and is usually anteriorly located. The maximum depth of the bulge is measured by the distance between the tip of the rectocele and the mid-anal canal. Rectocele measurements up to 2 cm on straining are considered normal. Defecography identifies the retention of contrast within the rectocele postdefecation. Van Dam et al. used the following grading system: grade 0 represented no evacuation of contrast; grades 1, 2, and 3 represented poor, moderate, or subtotal evacuation, respectively; and grade 4 occurred if there was no contrast retention in the rectocele after defecation. Digital manipulation may be needed to empty the rectocele. The anorectal angle (ARA) is the angle formed by the junction of the rectum and anus. At rest this angle may be 70 to 140 degrees and with straining this angle increases to between 100 and 180 degrees. As a result of the wide variations reported, the ARA measurements have little clinical significance. However, a change in the ARA is noted. The inability to relax the puborectalis muscle during attempted evacuation leading to poor rectal emptying makes the diagnosis of nonrelaxing puborectalis. Perineal descent is calculated as the distance of the perpendicular drop from the pubococcygeal line to the anorectal junction with a descent of more than 3 cm in the resting phase considered abnormal or more than 3 cm from baseline on straining. Intussusception is reported as invagination of the rectal wall into the anal canal whereas rectal prolapse refers to invagination of the rectum beyond the anal sphincter muscles. Rectal prolapse can be missed if the technician does not allow adequate time for straining or if the images are not taken low enough to visualize the anus. (See Videos 2-3 and 2-4 for demonstrations of normal defecography demonstrating landmark features and anatomy and defecography demonstrating a rectocele and enterocele. 
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