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1 Acta Radiologica ISSN: (Print) (Online) Journal homepage: Defecography X.-M. Yang, K. Partanen, P. Farin & S. Soimakallio To cite this article: X.-M. Yang, K. Partanen, P. Farin & S. Soimakallio (1995) Defecography, Acta Radiologica, 36:5, To link to this article: Published online: 04 Jan Submit your article to this journal Article views: 512 View related articles Full Terms & Conditions of access and use can be found at

2 Acra Radiologica 36 (1995) Printed in Denmark. All rights reserved Copyrighi 8 Acru Rerli~ilogim 1995 ACTA R A DIOLOG I CA ISSN Review Article DEFECOGRAPHY X.-M. YANG, K. PARTANEN, l? FARIN and S. SOIMAKALLIO Department of Clinical Radiology, Kuopio University Hospital, Kuopio, Finland. Abstract Defecography, a dynamic imaging modality, plays an important role in the diagnosis of functional and morphologic abnormalities of the anorectal region. We have here summarized the principle and techniques as well as observations of defecography, with special emphasis on morphologic measurements, clinical relevance, and limitations. The application of MR imaging in examination of anorectal function has also been addressed. Key words: Anus, defecography; MR imaging; pelvis; rectum. Correspondence: Xiao-Ming Yang, Clinical Radiology, Kuopio University Hospital, FIN Kuopio, Finland. FAX * Accepted for publication 15 December Defecography is a dynamic radiologic investigation performed during voluntary evacuation of the rectum. Some authors have called it evacuation proctography (26), dynamic proctography (13), and voiding proctography ( 1). This modality was originally described by WALLDEN in 1952, who investigated the significance of an abnormally deep pouch of Douglas in disturbed defecation (55). During the 1960s, only a few additional papers were published on this topic (6-8). Since 1984, improvements and refinements in proctologic surgical techniques brought about new interest in defecography (10,23, 30, 32). Today, defecography is widely used as a routine imaging examination of the anorectal function. Anatomy and physiology of anorectum The rectum is approximately 12 cm long and follows the curvature of the sacrum and coccyx. The rectum usually extends 3 cm beyond the coccyx, turning posteroinferiorly to form the anal canal of 2 to 4 c mh length (34). Studies of fecal evacuation are based on func- tion of the pelvic floor muscles surrounding the rectum and anal canal and attached to the bony pelvis (10, 19). The levator ani muscle, consisting of the ileococcygeus and pubococcygeus as well as puborectalis muscles, is an important component of the pelvic floor. It anchors the rectum in the middle third of the pelvis (37). The puborectalis and the deep portion of the external sphincter muscle are fused together. Both muscles originate from the back of the symphysis pubis, proceed backward and downward along the upper part of the anal canal, forming a U-shaped loop termed the puborectalis sling behind the anorectal junction (12, 50). The puborectalis sling creates the anorectal angle by pulling the anorectal verge anteriorly, resulting in an anorectal angulation of 80 to 90 at rest (12, 17, 57). Any increase of intraabdominal pressure forces the anterior rectal wall against the upper anal canal, thereby effectively occluding it, as a flap valve effect (21). The rectosphincteric reflex, including both the internal and external sphincters, is mediated through spinal reflex pathways via the pudendal nerve and branches of S3 and S4. The external sphincter is 460

3 DEFECOGRAPHY believed to be more important than the puborectalis sling in maintaining fecal continence (1 1, 12). The anatomic features correlate closely with defecographic findings. During straining, laxity of the levator ani muscle is seen as a descent of the anorectal junction (10). The relaxation of the puborectalis muscle can be observed as an increase in the anorectal angle (1 8). The sphincter relaxation widens the anal canal. The opening function of these muscles converts the anorectum into a funnel-shaped structure which enables the passage of stool in combination with an increased intraabdominal pressure (1 7). Pathophysiology of anorectum The anorectal angle and the degree of perineal descent during defecation straining are the most frequently used indicators of physiologic status of the pelvic floor muscles. A reduction of the anorectal angle and/or a decrease of the perineal descent during straining may be evidence of an inability to relax the pelvic floor muscles due to the spastic pelvic floor syndrome or paradoxical reaction (25). This inability of relaxing pelvic floor muscles leads to obstructed defecation, i.e., constipation and obstipation (15, 31, 54, 56). In this condition, patients must strain heavily to defecate, causing further anorectal disturbances, such as rectal intussusception, rectocele, and anterior mucosal prolapse (18, 25). The latter may cause ischemia and ulceration of the rectum (18). The presence of an obtuse anorectal angle at rest and an excessive perineal descent during straining, descending perineum. syndrome, suggests weakening and increased laxity of the pelvic floor muscles due to a long period of excessive straining at fecal evacuation. This condition leads to incontinence. During defecation, the force of abdominal straining is mainly transmitted through the anterior rectal wall, easily causing temporary mucosal prolapse into the anal canal. In most cases, this is readily corrected by contraction of the pelvic floor muscles. When these muscles are weakened, as in the descending perineum syndrome, the anterior rectal wall continues to bulge into the anal canal and then rectal prolapse may develop (19, 21, 44). Procedures at defecography Preexamination approaches. To show the small bowel loops in the pelvis, the patient is given 500 ml barium contrast medium (BaS04 suspension) orally 1,hour before defecography. Opacification of the pelvic small bowel is considered complete when some barium is fluoroscopically identified in the right colon (10, 26). The purpose of showing the pelvic bowel loops is to detect enterocele. In women, a tampon soaked with contrast medium is placed in the posterior fornix of the vagina for localizing the vagina (10, 26). However, it has been suggested that the tampon can interfere with normal pelvic floor movements during defecography and thus obscure diagnostic information (1, 34). A water-soluble contrast medium gel has been formulated, composed of equal parts of a sterile, lowph gel intended for vaginal use and high-density water-soluble iodine contrast medium ( 1). The gelcontrast combination is easier to administer, even in elderly patients, and is more physiologic (34). The patient should be asked to void before defecographic examination to prevent compression of the rectum by a full bladder (27). Techniques of defecography With the patient in the left decubitus position, a thick barium paste (a stool-like semisolid contrast medium) is injected into the rectum using a plastic syringe connected to a catheter (9, 47, 53), or a caulking gun (10). GOEI et al. (18) used 300 ml thick barium paste, prepared by adding 50 g of a suspending carbopol agent into 5 liters of barium sulfate, and then mixed gradually with 340 ml of sodium hydroxide until a thick paste of ph 7 was formed. TING et al. (53) injected 150 ml thick barium paste, prepared by mixing 200 ml of potato starch with 250 ml of warm water, followed by adding 50 ml of a commercially available barium suspension. In order to attain fecal viscosity and a specific gravity of 1.2 g/cm3, KRUYT et al. (28) made their thick barium paste by adding Metamucil to BaS04 contrast medium in a ratio of 1:30. Before radiography, the position of the anal verge is indicated by attaching a metal marker to the skin with micropore tape (42). Then, the patient sits on a specifically designed toilet seat or commode, mounted on the footboard of a remotecontrol fluoroscopy stand in an upright position (12). Because of the great differences in radiolucency between the pelvic soft tissue and the air below the buttocks, the placement of a filter device is necessary to absorb the unwanted radiation from the region of the anal canal (5, 14, 53). Different defecographic seats or commodes have been constructed of various materials, such as wood (5), Plexiglas (14,45), lead (53) or a water-filled rubber ring (12, 17). Under fluoroscopy in the right lateral projection, the anorectal function is studied by either recording the defecation procedure on a videotape (53), or photographing the various stages of defecation with a 100-mm camera at a frame rate of 461

4 1 frameh or 1 frame12 s (17, 19). The images of the anorectal region are obtained 1) during squeezing, whereby the patient exerts maximal contraction of the pelvic floor muscles; 2) at rest, when the patient is asked to completely relax the pelvic floor muscles; and 3) during straining with complete evacuation of the rectal contents (16, 19). The defecographic measurements should be corrected by X.-M. YANG ET AL. Fig. 3. After several minutes of straining, an enterocele (E) is detected between the space of the vagina (V) and rectum (+). AR=anterior rectocele. Fig. ]. A large anterior rectocele (AR) associated with a rectal prolapse (+). V=vagina. Fig. 2. A small perineal herniation or posterior rectocele (+) associated with a mild enterocele (E). the incorporation of a midline radiopaque centimeter ruler into the commode (19, 51). Qualitative evaluation - rnorphologic changes of anorecturn The pathologic findings at defecography include anterior rectocele, perineal herniation (posterior rectocele), enterocele or sigmoidocele, anterior or posterior mucosal prolapse, intussusception, and rectal prolapse. An anterior rectocele is a more than 2 cm bulging of the rectum into the posterior wall of the vagina during defecation straining (26, 34) (Fig. 1). The cause of anterior rectocele is considered to be an anatomic weakness of the anterior wall of the rectum that allows expansion in the form of a pouch (33, 43). Patients with paradoxic reaction are frequently affected by this morphologic disorder because they must strain heavily to defecate. A perineal herniation, also termed posterior rectocele, is an abnormal prolapse1herniation of the posterior rectal wall or whole rectum through a levator ani defect during straining (43) (Fig. 2). An enterocele is defined as a cul-de-sac filled with small bowel or omentum herniating downward between the vagina and rectum (26) (Fig. 3). A sigmoidocele is a herniated cul-de-sac filled with sigmoid colon. Clear-cut differentiation between an enterocele and a sigmoidocele is difficult in defecography. The causes of enterocele or sigmoidocele may be prior pelvic surgery, such as hysterectomy, urethropexy, or ventral suspension of 462

5 DEFECOGRAPHY uterus or vagina. These procedures change the normal horizontal vaginal axis and pull the vagina more anteriorly, which exposes the cul-de-sac and leaves it vulnerable to the subsequent development of an enterocele. Chronically increased intraabdominal pressure from any cause and mesenteric lengthening may facilitate enterocele formation. Some authors placed rectocele and enterocele as well as sigmoidocele in the group of posterior compartment pelvic prolapse (26). Unlike a rectocele, which is usually most evident during evacuation, enteroceles are sometimes confirmed only with repeated straining for several minutes after evacuation. It is important, therefore, to instruct the patient to continue straining after evacuation for facilitating detection of enteroceles (10, 26). Anterior mucosal prolapse, also termed internal prolapse of the anterior rectal wall, is defined as an invagination of the anterior rectal wall into the rectal lumen or anal canal (45, 53) (Fig. 4). Posterior mucosal prolapse is rare (Fig. 5). Some authors also named a small perineal hernia as a posterior mucosal prolapse (43). The defecographic differentiation of an anterior rectocele and an anterior mucosal prolapse depends on the angle between the anterior rectal wall and the superior margin of the pouch of the rectocele or mucosal prolapse: an obtuse angle is associated with the anterior rectocele and an acute angle with anterior mucosal prolapse. When anterior and posterior mucosal prolapse occur together and cause anorectal obstruction, a rectal intussusception is confirmed (53). Some authors also named the rectal intussusception internal circular prolapse? (53) or internal proci- Fig. 4. A large anterior mucosal prolapse (+) seen during straining. R=rectum. Fig. 5. An intraanal rectal intussusception: the distal rectum invaginates into the anal canal (+). Two posterior mucosal prolapses (b) are also seen. dentia (10). When the leading point of the intussusceptum passes out through the anus, the condition is designated rectal prolapse (10, 16) (Fig. 1). Some authors differentiate the rectal prolapse from an anal prolapse: the anal prolapse involves only the anal mucosa, but the rectal prolapse involves all layers of the rectum (10). The difference is noticed on defecography as differing thickness of the intussusception. In anal prolapse the a.p. diameter of the intussusception does not exceed 1 cm, but in rectal prolapses the diameter is 2 to 4 cm (1 0). Rectal prolapse is usually easy to recognize at clinical examination, whereas rectal intussusception can be better detected during defecography. It is extremely difficult to demonstrate rectal intussusception during a physical examination or by observation with an endoscope or a barium enema (1 8, 45). The diagnosis of rectal intussusception in defecography should be based on a considerable circular infolding of the rectal wall toward the lumen during straining. When the rectal infolding invaginates into the anal canal, it is termed intraana1 rectal intussusception (17) (Fig. 5). A minimal infolding that disappears after the bolus has passed is probably caused by a transient prolapse of the mucosa and should not be considered pathologic (1 6). Milder intussusceptions are now considered normal (41). The causes of rectal intussusception and rectal prolapse are not fully under- 463

6 X.-M. YANG ET AL. stood. An abnormally deep pouch of Douglas, defective levator ani, insufficient attachment of the rectum, and redundancy of the sigmoid colon have been suggested as predisposing factors (2, 39, 46, 49). Solitary rectal ulcer syndrome (SRUS) is an entity consisting of a benign rectal lesion in the distal anterior wall of the rectum with common clinical complaints of rectal bleeding and a long history of defecation disorders (1 7, 18). Sigmoidoscopic manifestations in SRUS include ulcerative, erythematous, and erosive changes, which are usually located on the anterior wall within 10 cm from the anal verge (16, 18). The mechanism of ulceration in SRUS is thought to be a mechanical injury to the mucosa, resulting in pressure necrosis (17, 18). Two defecation disorders are considered possible causes of SRUS: rectal intussusception and the spastic pelvic syndrome (18). Invagination of the rectal wall in rectal intussusception causes rupture of submucosal vessels, ischemia, and ulceration (48). A persistent contraction of the muscle in the spastic pelvic syndrome results in inability to empty the rectum, leading the patient to repeat straining. The result of the repeat straining is the development of anterior mucosal prolapse, finally causihg ischemia and ulceration (18). Thus, defecographic examination can demonstrate some indirect findings of SRUS, including rectal intussusception and anterior mucosal prolapse as well as spastic pelvic floor syndrome. Based on the literature, we have summarized the frequency of different defecographic abnormalities in patients with defecation disorders in Table 1. The most common findings are anterior rectocele (28%) and intussusception (19 /0), followed by enterocele or sigmoidocele (7%), anterior mucosal prolapse (7%), and rectal prolapse (3%). However, 17% of patients with defecation disorder have a normal defecography. Fig. 6. Measurements of different morphologic parameters: the anorectal angle - posterior (ARAp), the anorectal angle - axis (ARAa), the maximum width of the anal canal (WAC), the maximum width of the rectal lumen (WRL), the size of rectocele (SR), the rectovaginal separation (RVS), and the level of anorectal junction (ARJ) from pubococcygeal line (PC line). Quantitative evaluation - measurements of anorectum In the analysis of defecography, various morphologic parameters of normal and pathologic anorectum are measured at rest and at different defecation stages of squeezing and straining (Fig. 6). FELT-BERSMA et al. (12) measured the anorectal angle (ARA) in 2 different ways: 1) an angle formed by the axis of the anal canal and a line along the posterior edge of the distal rectal wall, named the anorectal angle - posterior (ARAp); and 2) an angle between the axis of the anal canal and a line alone the longitudinal axis of the rectum, named the anorectal angle - axis (ARAa). ARAp is the most frequently measured angle in defecography (12, 13). There is a wide range of normal values for the ARA at rest, squeezing and straining (4, 10). For example, GOEI (15) stated that the ARAp values Table 1 Frequency of different defecographic Jindings in patients with defecation disorders Defecographic findings, YO Anterior Authors Patients, Normal Anterior Enterocele/ mucosal Intussus- Rectal (ref.) n rectocele Sigmoidocele prolapse ception prolapse EKBERG et al. (10) TING et al. (53) KELVIN et al. (26) GOEI & BAETEN 9 - (16) Total (1 7%) 138 (28%) 34 (7%) 35 (7%) 92 (1 9%) 16 (3%) 464

7 DEFECOGRAPHY in asymptomatic subjects are " at rest and " during straining. EKBERG et al. (10) reported that normal values for ARAa could vary between 70 to 140" with a mean angle of 114" at rest and 110 to 180" with a mean of 134" during straining. FELT-BERSMA et al. (12) found that ARAp was smaller than the ARAa both at rest and during straining. ARA is not influenced by age or sex (12, 19). By comparing the result of defecography to that of anorectal manometry, KRUYT et al. (28) concluded that there is a correlation between ARA and fecal continence. However, some authors state that defecographic measurements of ARA cannot be regarded as a reliable indicator of the complicated physiologic condition of the pelvic floor muscles (3, 15, 35, 36, 40). YOSHIOKA et al. (60) suggested using a computer-drawn centroid of the rectum instead of the posterior rectal wall. Even though the results using the centroid appear to be more consistent, there are theoretical problems with this concept not yet addressed. The pelvic floor motion or the perineal level position is determined by measuring the distance between the anorectal junction (ARJ) and the pubococcygeal line parallel to the longitudinal axis of the anal canal (20, 53). The anorectal junction is the apex of ARAp (19,41), and the pubococcygeal line is a line extending from the most inferior portion of the symphysis pubis to the last coccygeal joint or the coccyx tip (53, 58). Some authors used the ischial tuberosity as a reference point rather than the coccyx tip for measuring the position of the perineal level (26, 41). KRUYT et al. (27) preferred to relate the position of the anorectal junction to the symphysiosacral baseline instead of the symphysiococcygeal baseline. Some studies have demonstrated that the perineal descent during straining was not influenced by gender, age or patient group, and was not different between patients with obstipation and controls (3, 12). However, contrary reports have shown an increased perineal descent with age, incontinence, and constipation (29, 33). The size of the anterior rectocele is determined by measuring the distance between a line through the anterior demarcation of the anal canal and the most anterior point of the anterior rectocele (25), classified as small (<2 cm in depth), moderate (2-4 cm in depth), and large (>4 cm in depth) (26, 53). The size of anterior rectocele less than 2 cm is regarded as a normal variant (42). During defecation, the anal canal forms a funnel-shape with the wide portion at the proximal end, and the maximal diameter of the anal canal is usually referenced (19, 41, 45). The width of the anal canal is not significantly different either between patients with defecation disturbance and control subjects, or between male and female subjects (15). SHORVON et al. (52) found an open anal canal at rest with loss of contrast medium in 7% of healthy individuals. Radiologically, evacuation of less than 50% of the thick barium within 30 s is considered poor emptying or incomplete evacuation (41, 42). In a previous study, we measured the maximum width of the rectal lumen (WRL) because we expected that WRL could be a parameter for quantitative assessment of rectal emptying (59). Our study demonstrated a mean WRL of 4.7 cm at rest which decreased to 2.1 cm during straining. The diagnostic relevance of WRL at different stages of defecation needs to be investigated further. By planimetrically estimating the amount of retained barium, some authors correlated the retained volume to the patient's sense of incomplete emptying. They found that defecographic findings did not explain incomplete emptying, although the reproducibility of the planimetric method was good (53). The rectovaginal separation, a space between the vaginal posterior apex and the anterior rectal wall, is an indicator for detecting enterocele or sigmoidocele. If the separation is 2 cm or more after evacuation, an enterocele may be suspected. The depth of the enterocele is measured along an axis parallel to the opacified vagina, starting at the line of the rectovaginal separation (26). Unfortunately, there is a large variation in the patterns of anorectal function among healthy individuals, and there is a large interobserver variation in the measurements of the anorectal configuration during the defecographic examination. The interobserver variation of the ARA measurements is mainly due to variations in drawing the tangent to the curved caudal inner rectal wall (27). The study by GOEI (15) showed large intraindividual variations of measuring the anal canal width. Using kappa statistic analysis, we evaluated the reproducibility of measuring 5 anorectal morphologic parameters, including anorectal angle - posterior, anorectal angle - axis, maximum width of anal canal, maximum width of rectal lumen, and the size of a rectocele. Our results showed that the 5 parameters were not reproducible, because of the high inter- and intraobserver inconsistency (59). Defecographic measurements and observations should, therefore, be interpreted with caution and should not be used as the only criteria for treatment (13, 19, 34). Clinical relevance Table 2 presents the main symptoms associated with different defecographic findings. 465

8 Defecographic findings X.-M. YANG ET AL. Table 2 Clinical relevance of defecographic Jndings Morphologic changes Measurements Main symptoms Anterior rectocele RS >2 cm Incomplete evacuation Enterocele or sigmoidocele RVS >2 cm Backache and dragging sensation when Intussusception or rectal prolapse - upright, and relief by lying down Incomplete evacuation, constipation Descending perineum syndrome Spastic perineal floor syndrome ARA > 130" at rest and >155" during straining, ARJ >4 cm at rest No ARA and ARJ changes from rest to straining Fecal incontinence, constipation Constipation and obstipation RS=rectocele size; RVS=rectovaginal separation; ARA=anorectal angle; and ARJ=anorectal junction. The main symptom associated with a rectocele is a feeling of incomplete emptying (38). Anterior rectocele is a frequent dysfunction of pluriparas and often one of the main reasons for dyschezia in female subjects (57). In male patients, the pressure of the anterior rectocele pouch on the prostate gland, like a digital pressure, can produce disturbance of the prostate during defecation straining (9). Typical symptoms with enterocele or sigmoidocele are backache and a dragging sensation or a pressure sensation on the rectum when upright, diminishing on lying down (26). The most common symptoms of intussusception are incomplete emptying of the rectal ampulla and constipation (16, 24), because, during downward straining, the intussusceptum occludes the anal canal, preventing further evacuation of rectal contents. If intussusception and/or rectal prolapse result in SRUS, rectal blood loss and mucosal discharge occur (17). The treatment for the intussusception is the same as that for classic rectal prolapse: rectopexy and sigmoid resection with rectal fixation (34). In a normal subject, the ARJ at rest is located near or on the pubococcygeal line. In the descending perineum syndrome, the ARJ position is lower than 4 cm below the pubococcygeal line at rest and/or it descends more than 4 cm from rest to straining, while ARA is more than 130" at rest and more than 155" during straining (17, 19, 20, 26). These pathologic changes cause incontinence, manifested as daily uncontrollable loss of feces (17, 24, 34). The main treatment for this condition is to eliminate all straining during defecation. Suppositories may aid in defecation without straining (34). In patients with spastic pelvic floor syndrome or "puborectalis paradox", constipation is the main symptom (56). In this condition, the ARA does not increase and contrast medium is not evacuated during straining (1 5, 26). Biofeedback has recently become the therapy of choice for spas- tic pelvic floor syndrome (34). However, some authors have concluded that measurements of the anorectal angle and perineal descent during straining give insight into the pathophysiology of defecation but lack clinical relevance (12, 22, 41) because even in normal subjects, abnormalities of defecography can also be found (4, 33, 51). Role of defecography Different investigative procedures are available in detecting defecation disorder of the anorectum (Table 3). Among those, clinical history and physical examination cannot supply details of either anorectal morphology or anorectal function, except when rectal prolapse is directly observed. Proctoscopy or rectoscopy only presents the anorectal morphologic status without supplying the anorectal functional information. In contrast, physiologic examinations, such as anal manometry, the saline infusion test, rectal capacity measurement, and anal electromyography, supply Table 3 Different modalities for evaluation of defecation Morphologic Functional Examinations evaluation evaluation Clinical history and physical examination 2 - Proctoscopy or rectoscopy + - Imaging modalities barium enema + - defecography + + CT - MR + + Physiological examination anal manometry - saline infusion test - rectal capacity - anal electromyography

9 DEFECOGRAPHY only the anorectal functional information without revealing the anorectal morphologic status (12, 20, 28). A barium enema study, like proctoscopy or rectoscopy, is a static examination that does not allow detection of functional abnormalities of the anorectum (1 7). It is important that patients are sitting down during the examination procedure, since much of the physiologic nature of defecation is lost when the patient is lying down as for a standard barium enema (10). This can be overcome with defecography, in which the patient is studied while sitting. This is a more physiologic means of assessing rectal dysfunction (10). The main applications of defecography are 1) the functional detection of anorectal anatomic abnormalities as possible causes of defecation disturbances; and 2) as an anatomic guide to any necessary surgical procedure (1 5). Defecography is especially suitable for revealing rectal intussusception which can easily be treated with rectopexy (10, 12). Another main contribution of defecography is its use in detecting enteroceles and sigmoidoceles that are easily missed at physical examination and overlooked at surgery (26). In addition, some authors have shown that ARA can play a valuable role in deciding which surgical procedure is appropriate to restore fecal continence (28). The disadvantages of defecography are: 1) a wide range of the anorectal angle and ARJ position among healthy individuals; and 2) a large interobserver variation in measuring anorectal morphologic parameters (19, 27). Recently, reports have dealt with assessment of rectal function with MR imaging (27, 58). The advantages of MR imaging over defecography are as follows: 1) the patient avoids ionizing radiation; 2) opacification of the vagina and rectum is not necessary because gas is an excellent contrast medium; 3) the interobserver variation with MR imaging for the measurements of ARA and ARJ is far less than that for defecography; 4) movements of the posterior rectal wall at the level of the plica of Kohlrausch can be analyzed with MR imaging (27). However, MR imaging does not provide the detailed, physiologic information about the posterior compartment of pelvic prolapse, which is easily seen with defecography (26). Moreover, patients have to take a prone position during MR imaging, which cannot truly. reflect the natural anorectal function. In summary, defecography is a useful imaging modality for detecting anorectal functional and anatomic abnormalities as possible causes of defecation disturbances and for anatomically guiding anorectal surgery. 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