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بنام خدا
Defecography
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Overview:
• Definition • Anatomy • Method of assessment • Indication • Preparation • Instrument • Contrast media • Technique • Recording • Other technique • Technique pitfalls • Parameters • Abnormalities Findings
Definition: Dynamic rectal examination (DRE) or defecography or proctography.
• DRE provides a dynamic assessment of the act of defecation by recording the rectal expulsion of a barium paste. • DRE provides qualitative and quantitative information on the function of anorectal and pelvic floor function, and the effectiveness of the anal sphincter and rectal evacuation.
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Anatomy
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Method of assessment
• Barium enema • Colon transit time • MR defecography
Indications for dynamic rectal examination are:
1. Outlet obstruction (disorder of defecatory or rectal evacuation), caused by intussusception, enterocele or spastic pelvic floor syndrome. 2. To distinguish between anterior rectocele and enterocele. 3. Fecal incontinence combined with outlet obstruction in intra-anal intussusception.
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Preparation
• No bowel preparation was used • It was deemed more physiological to observe how anorectal morphology altered during defaecation without preparation. • Two hours prior to the examination the patient ingests 135 ml of liquid barium contrast to opacify the small bowel. • In females the vagina is coated with 30 ml amidotrizoic acid 50% solution gel. • The use of tampons and gauzes soaked in barium should be avoided, because they can impaire pelvic-function.
LEFT: Pathology is suspected because of a great distance between rectum and vagina. No oral contrast had been given. RIGHT: After ingestion of liquid barium contrast a large enterocele is seen.
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Instrument:
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Contrast media
• The ideal rectal contrast has to simulate stool in weight and consistency. • Barium paste approximates to the consistency of feces • (Evacu-Paste 100) is a convenient paste.
Recording
• The fluoroscopic screening of the rectum (one frame per second) and the function of the pelvic musculature and the continence mechanism is assessed. • The whole procedure of DRE should be recorded on video or DVD. • Dynamic recording enables the examiner to follow the movements of the rectum, facilitating the diagnosis of rectocele, enterocele and intussusception, as well as to evaluate the function of the anal sphincter. • The duration of examination is about 15 minutes.
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Technique (The four dynamic phases) • images are obtained with the patient at: 1. Rest 2. maximal sphincter contraction (squeezing) 3. maximal strain certain muscles (straining) 4. defecation (push the barium paste)
Procedure:
1. The barium paste is injected until the patient experiences discomfort due to rectal distension or until about 250 ml has been instilled. (Liquid barium sulphate (50 ml) was instilled into the rectum, which was then insufflated with air to drive the contrast material proximally and outline the rectal mucosa.) 2. Then, the patient is asked to sit on a special commode. It is important that the patient is sitting during the procedure, since much of physiological nature of defecation is lost when the patient is lying down.
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X-ray:
1. Initially the patient is screened in left lateral projection at rest without consciously contracting any pelvic muscles and a spot film is taken. 2. The patient then maximally contracts the pelvic floor muscles ('squeeze') which results in a more tense muscular diaphragm and in elevation of the entire pelvic floor a spot film or video is taken. 3. Then, a fast-film sequence was obtained during straining with closed sphincters .
defecation:
1. Finally the patient is asked to empty the rectum as completely as possible. 2. An estimate of the completeness of defecation and measurement of pelvic floor descent can be made.
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Rest, start of defecation and end of defecation
Additional x-ray:
• Additional oblique or anteroposterior (AP) views should be taken of any unexplained radiographic feature seen on the lateral views.
• An S-shaped rectum may simulate an intussusception in lateral projection.
• Some patients give a history of various unusual maneuvers (digital support of vagina or perineum) to aid defecation. (Allowing the patients to demonstrate the maneuvers).
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On the left lateral and an AP-view of a patient with an intussuseption on both views.
On the left lateral and an AP-view of a patient with an S-shaped rectum which simulates an intussuseption on the lateral view.
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Normal defecography.
• (A) At rest. • (B) Note the deeper impression exerted by the puborectal sling (arrow) and the cranial migration of the distal rectum during forced contraction. • (C) During straining with closed sphincters, caudal migration of the anorectal junction is seen (asterisk). • (D) During evacuation, the anal canal opens with loss of puborectalis impression.
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Interpretation
Parameters
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Anorectal angle
• The anorectal angle (ARA) is measured between the anal canal longitudinal axis and the posterior rectal line, parallel to the longitudinal axis of the rectum. • At rest = 90 - 100°. • maximal sphincter contraction (squeezing) = (70 - 90°) • maximal strain certain muscles (straining) = >100) • during defecation = (110 - 180°)
• ARA is an indirect indicator of the puborectal muscle activity.
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• Normal pelvic floor movements. • (A) Mid-sagittal T1- weighted SPGR image obtained at rest after IV administration show normal position of the bladder B, vaginal vault V, and rectum in relationship to the pubococcygeal line (white line). The black lines make the anorectal angle (ARA) and their crosspoint represents the anorectal junction (ARJ). • (B) Mid-sagittal T1- weighted SPGR image obtained during squeezing in the same patient show normal minimal elevation of the pelvic floor and sharpening of the ARA. • (C) Mid-sagittal T1- weighted SPGR image obtained during straining in the same patient show normal minimal descend of the pelvic floor and widening of the ARA.
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Perineal descent
• This is "the caudad movement of the pelvic floor (anorectal junction) straining". • Defecation normally involves a relaxation of the pelvic floor (levator ani), leading to descent of the perineum. • Normal perineal descent or elevation is less than 4 cm from the pubococcygeal line in either direction (superior or inferior). • less than 3.5 cm relative to the resting position, when the bony landmarks (bis-ischiatic line and tip of the coccyx). • Indirectly represents the elevation and descent of pelvic floor. • Its clinical significance is still controversial
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Findings of rectal descent:
• Horizontal rectum during push • Delayed or incomplete rectal emptying • Delayed or incomplete rectocele emptying • Rectum protruding into anal canal • Long rectum in the bottom three inches of the pelvis
Efficiency of emptying/evacuation
• Normally, there is 90-100% evacutaion of rectal contents.
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Anal canal width
• Again measured during maximal evacuation, this is usually less than 2.5 cm.
Anal canal length
This is measured during maximal evacuation.
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Abnormalities Findings
• Rectocele • Rectal prolapse • Sigmoidocele • Intussusception • Spastic pelvic floor syndrome (Paradoxical puborectalis contraction) Abnormal perineal descent
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Rectocele • This is the most common finding with this type of imaging. • A rectocele can be defined as an anterior or posterior bulge of the rectal wall beyond the extrapolated line of the wall. • Significantly more anterior rectoceles were found in female patients in males. • Almost always in females, this is an anterior rectoceles where the anteiror rectal wall bulges forward, into the vagina. • In males, the prostate gland gives more support in this area compared to the vaginal cavity, so rectoceles, especially anterior rectoceles are uncommon in males. Less commonly and in males, there may be posterior rectoceles, where the rectum bulges posteriorly. • Anterior rectoceles may occur in individuals without complaints of the anorectal region as a posiible normal phenomenon. This may only be a significant finding if there are symptoms of obstructed defecation. • Usually rectoceles greater than 3 cm and those that do not empty are clinically significant.
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Rectocele seen during straining (right)
Rectal prolapse/Internal rectal intussusception • The rectum may be seen to prolapse, whether internally or externally. • Intussusception of the rectum is an invagination of the rectal wall, which begins as a circular fold 6 to 8 cm up in the rectum and develops into a condition in which the entire rectal wall folds in towards the rectal lumen. • There can be difficulty differentiating between internal intussusception and a normal rectal fold. • The thickness of the intussusception is half the width of the intussusception (the intussusception is a doubled over layer of rectal wall). • The intussusception can be intra-rectal, intra-anal or finally extra-anal as a rectal.
1 : Intra-rectal intussusception, 2 : Intra-anal intussusception, 3 : Extra-anal intussusception (rectal prolapse)
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Enterocele and Sigmoidocele • Enterocele is a prolapse of peritoneum that contains a section of small intestine. Sigmoidocele is a prolapse of peritoneum that contains a section of sigmoid colon. • In females, these prolapses usually descend between the rectum and the vagina. • An enterocele is a peritoneal sac that has herniated downwards along the ventral rectal wall. As DRE is routinely performed with small bowel and vaginal contrast, loops of small bowel are then seen to fill the gap between the vagina and the rectum. • Grade 1 is maximally reaching down to the distal half of the vagina, and partial or complete reduction of the rectal lumen. Grade 2 is as grade 1, but reaching down to the perineum. Grade 3 is protruding out of the anal canal to form a rectal prolapse.
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Normal findings at rest (left); during defecation there is a rectocele, that is pushed downward by an enterocele .
Spastic pelvic floor syndrome
• On the left a schematic lateral view on the levator ani and external sphincter ani muscles is shown. The puborectal muscle should be contracted at rest (sharp anorectal angle). During defecation the puborectal muscle should relax allowing passage of the stool.
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Spastic pelvic floor syndrome Dyskinetic Puborectlis Muscle Syndrome
• The puborectal muscle should be contracted at rest (sharp anorectal angle). • During defecation the puborectal muscle should relax allowing passage of the stool. • Spastic pelvic floor syndrome denotes a persistent contraction of the pelvic floor muscles during defaecation. • It represents a functional disorder of the pelvic floor muscles causing an outlet obstruction.
• Characteristic findings of defecography include a lack of pelvic floor descent and paradoxical contraction of the puborectalis muscle. • Another less specific feature is an aberrantly deep impression of the puborectalis sling on the posterior rectal wall at rest. • The etiology is unknown. Psychological factors may play a role.
• Evacuation time longer than 30 seconds is highly predictive of dyskinetic puborectalis muscle syndrome, having a positive predictive value of 90%.
Anismus (pelvic floor dysynergia)
• People with a tight internal anal sphincter have a big bowl-shaped rectum that empties slowly through a narrow, short anal )کاسه ای) opening that never opens up. • The patient may not be able to relax under the conditions, leading to relaxation failure of puborectalis and false positive diagnosis of anismus. • It has also been reported that there is a high false positive rate of anismus diagnosis with anorectal manometry for similar reasons.
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LEFT: Hypertonic sphincter (during defecation). RIGHT: Impression of hypertonic puborectal muscle (non-relaxing during defecation).
• Note abnormally deep puborectal impression (arrow) at rest (A) and at evacuation phase (B). During evacuation phase, there is lack of pelvic floor descent.
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Descending perineum syndrome Excessive pelvic floor descent during defecation is often caused by pudendal nerve injury resulting from a combination of obstetric trauma and chronic straining.
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• Defecation normally involves a relaxation of the pelvic floor (levator ani), leading to descent of the perineum. "the caudad movement of the pelvic floor or the anorectal junction during straining" • From the proctogram, descent is calculated by drawing an imaginary line (the pubococcygeal line) between the most inferior point on the pubic bone and the tip of the coccyx. • Normal perineal descent or elevation is less than 4 cm from the pubococcygeal line in either direction (superior or inferior).
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• If the perineum descends >3.5 or 4 cm, descending perineum syndrome may be diagnosed. • The anorectal angle is more than 130° at rest and increases to more than 155° during straining. • Incontinence is frequently associated with this syndrome.
Patients with or without abnormal perineal descent had similar frequencies of Rectocele, rectal prolapse, rectal intussusception, and enterocele.
42-year-old woman with fecal incontinence after perianal fistula repair. Black line indicates pubococcygeal line. Midsagittal T1-weighted SPGR image obtained 1-at rest shows normal position of bladder, vaginal vault, and anorectal junction (arrow) in relation to pubococcygeal line. 2- during squeeze shows normal elevation of pelvic floor and sharpening of anorectal angle. 3- during strain shows normal minimal descent of pelvic floor. 4- during defecation shows abnormal descent of anorectal junction (long white arrow) and vagina (solid black arrow), moderate rectocele (open arrow), and moderate cystocele
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Megarectum
• This is excessive width (>9 cm) of the rectum at the level of the distal sacrum and incomplete evacuation.
Y.Zahedpasha.M.D.Oct.2007
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