1. The presence of two or more of the following characteristics during the previous 3 months but with onset at least 6 months previously
(a) Straining associated with at least 25 % defecations
(b) Hard or lumpy stools associated with at least 25 % defecations
(c) Feeling of incomplete evacuation associated with at least 25 % defecations
(d) Sensation of anorectal obstruction associated with at least 25 % defecations
(e) Manual maneuvers to facilitate at least 25 % defecations (e.g., digital evacuation, manual raising of the pelvic floor)
(f) Fewer than three bowel movements per week
2. Loose stools are rarely present without laxatives
3. Insufficient criteria for a diagnosis of irritable bowel syndrome (IBS)
1 Unit of the Pelvic Floor
The pelvic floor, home of the anatomical structures devoted to defecation, is schematically divided into three compartments: anterior, middle, and posterior. The first compartment includes the bladder; the second, uterus and vagina; the third, anus and rectum. Fascial and muscular structures hold together and support these three sectors. The fascial structures consist of the endopelvic fascia with its different locations and functions (Stoker et al. 2001).
The muscular structures include the urethral muscles, the bulbospongiosus and ischiocavernous muscles, the superficial and deep transverse muscles, the anal sphincters, and the main muscle that keeps together the pelvic floor for its insertions and functions: the levator ani (Strohbehn 1998).
The female pelvic cavity in the course of evolution had to adapt to three fundamental requirements: acquiring a functional conformation at orthostatic position, being able to accommodate the development of the fetus, and allowing the performance of labor with a capacity space much more limited compared to that of other mammals (Schimpf and Tulikangas 2005). It follows that a failure of the supporting structures may determine a competition between prolapsing organs to occupy the limited pelvic space (crowded pelvis syndrome) (Kelvin and Maglinte 1997). For this reason some prolapses are clinically silent and/or hardly appreciable by clinical examination. A surgery that repairs the clinically manifest alterations can, by freeing up space, unmask the silent ones. Anatomical defects that are not repaired for being silent can become symptomatic over a relatively short time (Withagen et al. 2010). The frequency of alterations in other compartments associated with difficult evacuation is high: 95 % of patients have multiple compartmental defects (Maglinte et al. 2011). Clinical evaluation and physical examination are the first approach to pelvic floor disorders, but physical examination is insufficient for understanding the causes of the evacuative alterations, and the prolapses can be underestimated or not diagnosed at all (Kelvin et al. 1999). Whatever the method of approach adopted, be it clinical or instrumental, it must take into account the influence of gravity on the descent of the pelvic floor and on the expression of each structural alteration. The examination in supine position can restrict or prevent such events and make it difficult to assess them. The sitting position instead allows for the complete relaxation of the pelvic muscles during the thrust phase, allowing the full expression of the prolapse (Maglinte et al. 2011, 2013; Ribas et al. 2014).
2 Barium proctography
The introduction of barium proctography dates back to the 1960s, but its standardization took place in the early 1980s thanks to P. Mahieu et al. (1984a, b).
This technique began with the study of rectoanal dysfunctions and evolved progressively extending to the study of the bladder, the vaginal axis, and the prolapse of the small bowel and sigma (dynamic cystoproctography) (Maglinte et al. 1997). With this technique it is possible to obtain a single view of all the organs supported by the pelvic floor and to identify clinically silent prolapses.
Barium proctography without opacification of the bladder, but with opacification of the small intestine, the vagina, and the anorectal region, is currently considered the gold standard for the study of the morphological and dynamic anorectal dysfunction (Maglinte and Bartram 2007).
2.1 Clinical Indications
- 1.
Obstructed defecation: rectoanal obstacle to evacuation, incomplete emptying, prolonged defecation effort, use of manual maneuvers to aid the expulsion of the feces.
- 2.
Light incontinence (in serious incontinence the retention of barium is impossible). The exam is indicated especially in cases where ultrasound and endoanal manometry do not detect significant sphincter damage (Terra and Stoker 2006). In about a third of the cases, obstructed defecation and incontinence are both present (Siproudhis et al. 2006; Shorvon and Marshall 2005).
- 3.
Operated patients: the exam is indicated in patients who have received surgery for anorectal reconstruction (e.g., ileal pouch) and have evacuative difficulties or in patients operated for obstructed defecation who, because of failure or complications of surgery, need reassessment (Shorvon and Marshall 2005).
- 4.
Chronic or frequently recurrent proctalgia. Dyssynergic defecation is the main cause of pain in most patients (Shorvon and Marshall 2005). Besides the dyssynergia that can be present even in absence of constipation (Chiarioni et al. 2011), if the cause is a solitary rectal ulcer an intussusception can be found (Womack et al. 1987).
2.2 Technical Aspects
The examination requires a comfortable dedicated radiolucent commode on which the patient sits and performs the defecation act (Mahieu et al. 1984a) (Fig. 17.1).
Fig. 17.1
Barium proctography . The commode for the proctography is located on the platform of the upright radiological table. Below the bolster of the commode is placed a rubber donut filled with water to increase the contrast and improve the quality of the images
The evening of the day before the exam the patient carries a rectal cleaning enema. Some authors prefer the introduction of a laxative suppository about an hour and a half before the exam (Maglinte et al. 2011).
An hour before the examination the patient drinks a diluted barium suspension.
In our center, in this hour of waiting, medical history is collected, and the examination and its purposes are explained to the patient; a clinical examination of the pelvic floor is performed in order to be compared with the results of the barium proctography. A pelvic ultrasound is performed to highlight the presence of a cystocele, of a uterine prolapse (when the uterus is clearly visible), or of a peritoneocele containing or not bowel loops; an initial assessment of the posterior pelvic compartment by ultrasound is also performed.
About an hour after the barium was ingested, we proceed to the opacification of the vagina and rectum, respectively, with 20–30 and 200–300 cc of density semisolid barium pasta (by analogy with the fecal material) that we prepare with a mixture of 100 g powder of barium sulfate, 100 ml of water, and 100 cc of ultrasound gel. Some authors resort to a semisolid mixture of barium and potato starch (Mahieu et al. 1984a). For administration we use 50–60 cc syringes and the cannula attached to the barium bag. Some authors, and we among them, prefer not to stick to a standard quantity but proceed with the introduction until the patient feels the urge to evacuate; the purpose is to facilitate the stage of evacuation, making it as similar as possible to the physiological one. If a radiological study of the anterior compartment is required, we proceed to the retrograde opacification of the bladder. After the insertion of a Foley, iodinated contrast is introduced. The quantity is about 30 ml if the purpose is only to investigate the presence of a cystocele (Maglinte et al. 2013); in order to study also the voiding phase, the mobility and the morphology of the urethra, between 100 and 150 cc of contrast medium is introduced, so that the patient feels the urge to urinate. To avoid interference between compartments, it’s best to run the study of the emptying of the organs separately, filling them in subsequent times: after the rectum-emptying assessment, the bladder is filled with contrast medium for its static and dynamic evaluation.
The barium proctography includes three initial radiographs, one at rest (Fig. 17.2), one during voluntary contraction (to assess the contractile ability of the puborectalis sling) (Fig. 17.3), and one in straining (to assess the activities of the external anal sphincter) (Maglinte et al. 2011). Not all authors consider the phase of straining to be useful, because of the difficulty for some patients to push for fear of losing the contrast medium (Maglinte et al. 2011). In the next phase of the evacuation, the patient, at the invitation of the operator, empties the rectum (Fig. 17.4). The descent of the anorectal junction, the opening of the anal canal, the enlargement of the anorectal angle, and the emission time of the contrast medium are evaluated. The evacuation is a complex physiological process based on the interaction between the colonic and rectal activities. In barium proctography it’s possible to evaluate only the emptying of the extraperitoneal rectum, showing the passive emptying induced by voluntary abdominal pressure. The retention of barium above the fold cross of the Houston valve (plica border of this part of the rectum) is of no significance in the exam assessment (Maglinte and Bartram 2007).
Fig. 17.2
Barium proctography . Normal proctogram. Resting rectal position. The anorectal angle (ARA) is located between the longitudinal axis of the anal canal and the posterior wall of the rectum. The pubococcigeal line (continuous line) extends from the bottom edge of the pubic symphysis to the coccyx. The position of the anorectal junction is measured by tracing the perpendicular line (dotted line) between the pubococcygeal line and the anorectal junction; v vagina
Fig. 17.3
Barium proctography . Normal proctogram. Voluntary contraction phase: (a) the amplitude of the angle is reduced and (b) the anorectal junction ascends compared to the resting condition
Fig. 17.4
Barium proctography . Normal evacuation. The amplitude of the anorectal angle increases and the anorectal junction descends if compared to the resting condition. The anal canal opens within 5 s since the start of the push and the evacuation is completed within 30 s
The evacuative or dynamic phase is recorded with a digital system of serial acquisitions (one image per second for 30 seconds) or with videotape. The system is calibrated to compensate for the radiographic magnification (Maglinte and Bartram 2007).
2.3 Evaluation Parameters
2.3.1 Pubococcygeal Line
In order to identify the location of the anorectal junction at rest and during the emptying phase, a reference line, called pubococcygeal, is drawn between the lower edge of the pubis and the most visible coccygeal articulation. Some authors prefer to use, as extreme tail of the line, the sacrococcygeal articulation, in order to prevent the mobility of the coccyx. In both cases the line is chosen because it closely approximates to the position of the levator ani, which is the plane of reference for the assessment of the descent of the pelvic organs (Maglinte et al. 2013; Kelvin and Maglinte 2000).
The descent of the posterior pelvic floor is measured by drawing the perpendicular line between the anorectal junction (boundary between the rectum and the anus) and the pubococcygeal line. The normal value at rest does not exceed 3–4 cm (Kelvin and Maglinte 2000). Later this measurement is performed on the radiogram of the evacuation phase. The descent of the anorectal junction normally does not exceed 3–4 cm (Kelvin and Maglinte 2000). There are authors who prefer to use, as a reference line, the floor of the commode or the line through the ischial tuberosities (Maglinte and Bartram 2007; Shorvon and Marshall 2005); the reason is that, before the introduction of digital radiology, the pubis was not always identifiable. The anorectal junction at rest normally does not drop below the ischial tuberosities; the evacuative excursion does not exceed 3–4 cm (Shorvon et al. 1989).
The radiologically detected mobility on healthy subjects in position of defecatory excursion is greater than the one detected clinically (Shorvon et al. 1989).
2.3.2 Anorectal Angle (ARA)
It is the angle between the longitudinal axis of the anal canal and the tangent to the posterior margin of the rectum. It is due to the activities of the levator ani; indirectly it provides an assessment of the function of this muscle, by reducing during the voluntary contraction and widening during the emptying (phase that corresponds to the complete relaxation of the muscle complex). The normal and pathological values of this angle largely overlap, making, according to some authors, its measurement of little use (Felt-Bersma et al. 1990; Bartram et al. 1988).
The normal values are at rest (80°–120°), emptying (115°–150°), and squeezing (75°–104°) (Habib et al. 1992).
2.3.3 Length of the Anal Canal
Normal values at rest are between 10 and 38 mm in men and from 6 to 26 mm in women (Shorvon et al. 1989).
2.3.4 Diameter of the Anal Canal
The closing state of the anal canal is evaluated in resting conditions. The normal opening diameter during evacuation is between 8 and 18 mm (Piloni et al. 1993).
2.3.5 Transverse Diameter of the Rectum
It corresponds to the distance between the front and the rear wall of the average rectum. Normally it does not exceed 6.5 cm (Piloni et al. 1993).
2.3.6 Rectosacral Space
It is the space between the rear wall of the rectum and the sacral concavity at S3 level; it does not exceed 10 mm in conditions of rest (Shorvon et al. 1989).
2.3.7 Evacuation Times
They include the time of opening of the anal canal and the time between the beginning of the act of expulsion and the end of the discharge; the latter is determined by the complete emptying of the ampoule, by the perception of completeness of the evacuative act, or by a hindrance in the rectoanal region arisen during the expulsion. The average latency in the opening of the anal canal does not exceed 3–5 s. The actual time of evacuation is less than 30 s with an average value of 11 s (Bartram et al. 1988).
2.3.8 Evacuative Residue
The evacuative residue does not exceed one-third of the normal released quantity. It is calculated with planimetric measures. The difference between the radio-opaque rectal area before and after the emptying is comparable to the difference between the weight of the introduced barium and that of the expelled barium (Halligan et al. 1994).
In a recent study (Palit et al. 2014) conducted in healthy volunteers, the average total time of evacuation was 88 s in men and 128 s in women. The average percentage of total evacuation was 71 % in men and 65 % in women. The study shows a broader range of efficiency of evacuation than in previous reports. The probable explanation is that the administration of contrast medium was not a quantitative standard but varied in relation to the perception of a sustained desire to defecate. It is likely that this diversity caused the wide variability (Palit et al. 2014).
2.3.9 Pattern of Evacuation
In normal subjects, three evacuative patterns have been described: type 1 characterized by the rapid opening of the anal canal and rapid evacuation of the contrast medium, type 2 defined as “pulsating” (emission of small amounts of contrast medium during short and successive time intervals), and type 3 characterized by continuous but slow evacuation (Palit et al. 2014).
3 Functional and Structural Anorectal Abnormalities
Anorectal abnormalities, mainly appreciable during evacuation, are both structural and functional.
3.1 Functional Abnormalities
The beginning of defecation takes place with the voluntary contraction of the abdominal muscles, the voluntary relaxation of the pelvic muscles, the descent of the anorectal junction, the expansion of the anorectal angle, and the opening of the anal canal. When the patient stops the straining, restores the normal tone of the anal sphincters, and lifts the anus, the anal canal closes, and the anorectal angle decreases. The anorectal junction returns to its resting position (postdefecation reflex) (Maglinte et al. 2011).
Functional abnormalities represent an alteration of the physiological evacuative function.
According to the Rome III criteria they include
- 1.
Dyssynergic defecation
This is the inappropriate contraction of the pelvic floor muscles (anal sphincter and/or puborectalis muscle) or the partial reduction of the basal pressure of the anal canal during the expulsive push (Fig. 17.5).
Fig. 17.5
Barium proctography . Dyssynergic defecation. The lateral radiogram shows the accentuation of the puborectalis impression (white arrow) during the maximum thrust and the reduced opening of the anal canal (ac). The evacuation time is longer than 30 s. There is a rectocele (r) from distension. It is positioned above the hymen plane
- 2.
Impaired defecation by inadequate propulsion
This is the increase of the intrarectal pressure caused by an inadequate contraction of the muscles of the abdominal wall, with or without signs of dyssynergic defecation.
These alterations can be detected by manometry, some from electromyography, and partly by imaging techniques (RAO).
3.1.1 Dyssynergic Defecation
A plethora of terms were used in the past to indicate dyssynergic defecation, namely, inappropriate contraction, failure or insufficient relaxation of the puborectalis muscle and/or of external anal sphincter, anismo, dyssynergia of pelvic floor muscle, paradoxical contraction of puborectalis muscle, puborectalis syndrome, and spastic pelvic floor syndrome (Rao and Meduri 2011).
The term “dyssynergic defecation” is better fit to describe the plurality of the muscles involved and the alteration of their coordination (Rao and Meduri 2011).
Signs of Dyssynergic Defecation
Initially the defecographic signs indicated as diagnostic elements were the accentuation of the puborectalis impression and the reduction of the ARA during the evacuation (Mahieu et al. 1984b).
The puborectalis impression is the indentation that the puborectalis muscle forms immediately above the anorectal junction, on the rear side of the rectum (Shorvon et al. 1989). Normally, with the beginning of the expulsion phase, in conjunction with the relaxation of the muscle, this impression disappears (Mahieu et al. 1984b).
In some cases of dyssynergic defecation, the persistence of this footprint has been observed (Mahieu et al. 1984b). Halligan et al. subsequently found that this sign is not useful to differentiate individuals with functional alterations from healthy ones (Halligan et al. 1995a, 2001). The parameters that have proved to be more sensitive to this diagnosis are the prolonged evacuation (>30 s) and the partial removal of the contrast medium (<60 %). The association of the prolonged evacuation with the incomplete emptying has a positive predictive value of 90 %. Another sign that’s present, although not constant, is the reduced opening of the anal canal (Halligan et al. 2001).
Of the various methods used for the diagnosis of dyssynergic defecation (imaging techniques, balloon expulsion test, manometry, electromyography), none can be considered the gold standard for diagnosis. The reliability of the diagnosis is given by the concordance of more techniques (Rao and Meduri 2011).
3.1.2 Altered Defecation by Inadequate Propulsion
A normal evacuation requires an adequate intrarectal pressure and anal muscle relaxation. The pressure increase achieved by the voluntary contraction of the diaphragm and of the abdominal muscles causes an increase of the intrarectal pressure. Halligan et al. described an altered defecation characterized by prolonged emptying time, descent of the anorectal junction below 3 cm, and intrarectal reduced pressure in the absence of other changes (Halligan 2008). Faucheron et al. described a very similar form of evacuative alteration, defined as rectal akinesia (Faucheron and Dubreuil 2000).
In the same patient a reduced intrarectal pressure and a paradoxical contraction or insufficient relaxation of the pelvic muscles can coexist (Bharucha and Pemberton 2013).
3.2 Structural Anorectal Abnormalities
3.2.1 Descending Perineum
It is the condition where, during the evacuation, the anorectal junction descends more than 3–4 cm compared to the resting position.
3.2.2 Descended Perineum
The anorectal junction at rest appears positioned more than 3–4 cm below the pubococcigeal line or the ischial tuberosities (Fig. 17.6).
Fig. 17.6
Barium proctography . Lateral proctography at rest. Descended perineum: the anorectal junction appears to be located 8 cm below the pubococcygeal line (nv < 4). It’s a sign of weakness of the muscular-fascial supports of the pelvic floor. A protrusion (p) of the rectal anterior wall is also present, indicating that the rectovaginal septum had already failed in resting conditions
The descended perineum is considered to be the consequence of a structural failure of the muscle-fascial supports of the pelvic floor, as a result of protracted efforts during the evacuation. These efforts can also cause the stretching of the pudendal nerve with secondary neuropathy (Halligan 2008).
With aging, the frequency of the descended perineum grows and the frequency of the descending perineum decreases, due to the loss of elasticity of the muscle-connective tissue support. The pudendal neuropathy can evolve into the sphincter denervation, resulting in incontinence (Pemberton 1990). Other factors that can damage or weaken the pelvic floor are childbirth, high BMI, nutritional deficiencies, and diseases of the collagen (DeLancey et al. 2007).
3.2.3 Megarectum
Megarectum is an alteration in which the transverse medium rectal diameter is greater than 6.5 cm (Piloni et al. 1993). It is a condition rarely seen in healthy subjects. A transverse diameter greater than 8.1 cm in an adult male and 6.9 cm in an adult woman should lead to further investigation (Palit et al. 2014). It can be associated with an increased threshold in the rectal sensitivity, which can cause evacuative difficulties (Meunier et al. 1979).
3.2.4 Increase of the Rectosacral Space
A rectosacral space greater than 1 cm can be a sign of a large mesorectum and can be associated with an external rectal prolapse (Mackle and Parks 1986).
3.2.5 Rectocele
Rectocele is the herniation into the vagina of the anterior rectal wall; it is associated with herniation of the posterior vaginal wall (posterior colpocele). In addition to the rectocele, the posterior colpocele can be associated with enterocele, sigmoidocele, or peritoneocele.
The rectoceles can be classified according to position (low, medium, high), size (small <2 cm, medium 2–4 cm, large >4 cm), or degree (type I with bulging in the upper vagina, type II extending to the vaginal introitus, type III extending beyond the vaginal introitus) (Zbar et al. 2003). Rectoceles smaller than 2 cm are a normal finding in nulliparous women (Shorvon et al. 1989). A useful subdivision for the clinical diagnosis is the distinction in rectocele by distention, rectocele by displacement, and mixed rectocele (Maglinte et al. 2013). The first type is associated with dyssynergic defecation (Pucciani et al. 1996). The vaginal apex and the uterus are in the normal position. This type of rectocele is the consequence of a chronic evacuative effort. It is positioned above the hymen. The second type, rectocele from dislocation, is the result of damage to the rectovaginal septum at childbirth. It is located below the hymen and associated with failure of the pelvic floor muscles and of the perineal body (Marti et al. 1999) (Fig. 17.7). It results in excessive descent of the vaginal apex and of the uterus. The third type, the mixed type, is caused by a failure of muscle tissue caused by dyssinergic defecation (Fig. 17.8). The type 2 rectocele shows a broader anorectal angle at rest and during evacuation, greater descent of the anorectal junction, and a more frequent association with intussusception: 61 % of the cases (Pomerri et al. 2001).
Fig. 17.7
Barium proctography . Lateral radiograms during the evacuation. Rectocele: herniation into the vagina (v) of the anterior rectal wall. Rectocele from dislocation: the rectocele protrudes 2 cm beyond the hymen plane (parallel line to the longitudinal axis of the pubis (P), passing through the posterior margin of the vaginal fork) (h); an excessive descent of the vaginal apex can be observed. This type of rectocele is the result of damage to the rectovaginal septum after childbirth. In anterior vaginal axis dislocation corresponding to posterior vaginal prolapse (pvp)
Fig. 17.8
MR proctography. Fast T2 sequence weighted on the midsagittal plane, obtained in patients with dyssynergic defecation. A large rectocele filled with contrast pushes forward the posterior vaginal wall and stretches of the perineal body without emptying. The anterior wall of the rectocele extends beyond the plane of the hymen. It’s a mixed rectocele
Symptomatic Rectoceles and Their Measurement
Rectocele occurs most frequently during evacuation. A large rectocele is more likely to be symptomatic. The size of the rectocele is measured as the distance between the extended line of the anterior border of the anal canal and the tip of the rectocele (López et al. 2001) or, according to other authors, from the ideal line demarcating the normal position of the anterior rectal margin (Shorvon et al. 1989) (Fig. 17.9a, b). The first measurement is easier to achieve, but it overestimates the true depth of the rectocele. The evaluation is completed by measuring the width of the rectocele, that is, its height starting from its basis (Palit et al. 2014). The percentage of emptying is measured by the difference of its area before and after the evacuation. A normal retention should not exceed 10 % of the initial area (Halligan et al. 1994). The amount of the retained contrast medium is considered, however, extremely variable even in asymptomatic subjects; the evacuative difficulties cannot be evaluated only on the basis of this retention. Also, there is no consensus on the relationship between the size of rectocele and the emptying (Greenberg et al. 2001).
Fig. 17.9
Barium proctography . Measurement of the rectocele: (a) distance between the extended line of the anterior border of the anal canal and the tip of the rectocele. This measurement is easier to achieve, but it overestimates the true depth of the rectocele (b) distance between the ideal line demarcating the normal position of the anterior rectal margin and the tip of rectocele
An interesting pathophysiological observation is that rectoceles which do not retain barium do not show any difference in pressure compared to the proximal rectum; on the contrary, rectoceles with trapping in 64 % of the cases show a sharp drop in pressure compared to the proximal rectum. They behave as inert rectal pouches. However, no differences have been found in evacuative difficulty between the two groups (Halligan et al. 1995b). Regardless of the depth of the rectoceles, it was detected that an attempt of evacuation in the toilet, after the end of the examination, significantly increases the percentage of emptying (Maglinte et al. 2011).
Symptoms of the Rectoceles
A rectocele may determine a feeling of incomplete evacuation, use of digital maneuvers (introduction of the finger into the vagina and pressure on its posterior wall or lifting and thrust back of the perineum) to facilitate emptying. The surgery can improve the emptying of the rectocele and reduce the associated vaginal bulge (Van Laarhoven et al. 1999). The rectocele-dyssynergia association reduces the chances of success of the surgery (Karlbom et al. 1996).
Rectoceles in Males
Small rectoceles may be present also in men, especially after total prostatectomy (Cavallo et al. 1991).
3.2.6 Posterior-Lateral Herniations of the Rectum
They may result from a failure of the iliococcygeal muscle during childbirth. They are defined as ischiorectal hernia if they have a depth greater than 4 cm (Grassi et al. 1995).
3.2.7 Intussusception
Definition, Classification, and Morphology of the Intussusception
The intussusception is the introversion at full thickness of the rectal wall into the lumen of the rectum. The diagnosis of the intussusception, unlike that of the rectocele, happens at the end of the evacuative phase when the intussusception of the rectum is maximum and it is possible, thanks to the rectal emptying, to distinguish the invaginated segment from the segment that surrounds it (Kelvin et al. 1994). The invagination limited to the rectum is called intrarectal (Figs. 17.10 and 17.11); it’s called rectoanal if it enters the anal canal (Fig. 17.12). A more detailed classification of the intussusception is the one made by the Oxford Radiological Grading System. It includes five degrees: grade I corresponds to high rectorectal intussusception (the top of the invagination stops above the proximal edge of the associated rectocele); grade II, when the apex of the invaginated segment descends to the entrance of the rectocele; grade III, when the apex of the invaginated segment descends to the upper margin of the anal canal; grade IV, when the apex of the invaginated segment enters the anal canal; and grade V, when the invaginated segment protrudes outside the anal canal (it corresponds to the external rectal prolapse) (Shorvon et al. 1989).
Fig. 17.10
Barium proctography . Rectorectal intussusception. Lateral proctography reveals circumferential rectal infolding during evacuation. The intussusception is limited to the rectum and does not go below the upper rectoanal margin
Fig. 17.11
MR proctography. Fast T2 sequence weighted on the midsagittal plane, obtained at the end of the evacuation. Large cystocele (c) and rectorectal intussusception i) (the rectal walls fold into the rectum but do not enter the anal canal)
Fig. 17.12
Barium proctography . Rectoanal intussusception. The lateral proctography toward the end of the evacuation reveals the circumferential infolding of the rectal walls during evacuation. The apex of the intussusceptum enters the anal canal. Measurement (a) of the thickness (dashed line): distance between the edge of the intussuscipiens and the contour of the intussusceptum. The depth of the intussusception (b) (continuous line): distance between the starting point of the intussusception and the anorectal junction
This classification is useful to follow the evolution over time of the intussusception. Sometimes the rectum appears collapsed after emptying and still under pressure, and this can lead to suspect an intussusception. In these cases, to settle the question, the frontal radiogram is useful. It will show that a collapsed rectum looks like an inverted “3” that can be mistaken for an intussusception (McGee and Bartram 1993).
The intussusception is by definition circumferential. It can be predominantly front or rear. The thickness between the edge of the invagination and the surrounding segment is 3 mm or more.
Pathogenetic Hypothesis
The most credited pathogenetic hypothesis is that the intussusception is secondary to a lack of, or incomplete, relaxation of the levator ani resulting in straining during defecation and subsequent failure of the muscle-fascial structures of support (Pucciani 2008).
The evacuative difficulties may damage the anal sphincters over time. In some rectoanal intussusceptions, an excessive opening of the anal canal is observed (Pomerri et al. 2001).
Symptomatic Intussusceptions
The intussusception is present in 50 % of the asymptomatic population. In symptomatic subjects its thickness is significantly greater: the average anterior thickness is 8 mm versus 4 mm in asymptomatic subjects; the average posterior thickness is 5 mm versus 3 mm in asymptomatic subjects. There are no significant differences in the depth of the intussusception (Dvorkin et al. 2005a). The ratio between the diameter of the invaginated segment and the surrounding intestinal wall appears higher than 2.5 in symptomatic subjects (Pomerri et al. 2001).
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