Chapter 16 — Obstructed Defecation Syndrome (ODS)

Obstructed defecation syndrome means difficulty emptying the rectum, despite a normal urge to pass stool. The patient strains. The patient often does not empty fully, even after straining hard. This chapter explains obstructed defecation syndrome in full. It covers presentation, examination, differential diagnosis, investigations, and management. This is the same pattern used for every disease chapter in this manual.

16.1 What Is Obstructed Defecation Syndrome

Obstructed defecation syndrome is not one single disease. It is a group of conditions. Each condition blocks the normal passage of stool out of the rectum, in a different way.

Some causes are anatomical. Something physically blocks or traps the stool. A rectocele is one example. Rectal intussusception, described in Chapter 15, is another.

Some causes are functional. The pelvic floor muscles fail to relax properly during straining. This is called pelvic floor dyssynergia, or anismus. No physical blockage is present. The muscles simply work against the patient, instead of with him.

Many patients have more than one cause together. A rectocele and dyssynergia often coexist. Careful assessment separates them. This is essential, since treatment differs sharply between an anatomical cause and a functional one.

16.2 Why It Happens

A rectocele is a bulge of the front rectal wall into the back wall of the vagina. It forms where the tissue between the rectum and the vagina, called the rectovaginal septum, has weakened.

Childbirth is the leading cause of this weakness. A difficult delivery, a large baby, or an assisted delivery with forceps all add to the risk. Chronic straining, over many years, adds further strain to an already weak septum.

During straining, stool can push into the rectocele instead of moving forward and out. The stool becomes trapped in this pouch. The patient feels incomplete emptying, even after prolonged straining.

Pelvic floor dyssynergia has a different cause. The puborectalis muscle and the external sphincter should relax during straining. In dyssynergia, they contract instead. This is often a learned pattern, built up over years of habitual straining, rather than a structural problem.

Rectal intussusception, described in Chapter 15, can also obstruct defecation. The folding rectal wall itself blocks the passage of stool, acting much like a one-way valve that will not open properly.

A retroverted uterus can add to the picture in some women. Chapter 17 covers this specific cause in full detail.

16.3 Classification

Obstructed defecation syndrome is best classified by its underlying cause, since this decides the treatment.

Anatomical causes — a rectocele, a rectal intussusception, a rectal prolapse, or an enterocele, which is a pouch of small bowel that descends into the rectovaginal space.

Functional causes — pelvic floor dyssynergia, or a general disorder of rectal sensation and coordination.

Mixed causes — an anatomical finding, such as a small rectocele, together with a functional element, such as dyssynergia. This combination is common, and both parts need attention.

A rectocele itself is often graded by its depth on defecography. A small rectocele, under 2 centimetres, is common and often has no symptoms at all. A large rectocele, over 4 centimetres, is more likely to trap stool and cause symptoms.

16.4 Presentation

Follow the history-taking method described in Chapter 2. Certain features are typical of obstructed defecation syndrome.

A sense of incomplete emptying, even immediately after passing stool.

Prolonged, excessive straining, often for many minutes at a time.

A need to use digital support to complete defecation. The patient may press a finger against the perineum, or inside the vagina, to help push stool through.

A feeling of blockage, or of stool sticking, inside the rectum during defecation.

A need for repeated attempts to fully empty the bowel, sometimes returning to the toilet several times within an hour.

Use of laxatives, enemas, or manual evacuation, in a more severe or long-standing case.

Ask specifically about digital splinting. Many patients feel embarrassed to mention this. They will not volunteer it unless asked directly. Ask gently, following the approach described in Chapter 2.

16.5 Examination

Follow the sequence from Chapter 3. Several steps need particular attention for obstructed defecation syndrome.

See Chapter 4 for the inspection method. Ask the patient to strain during inspection. A rectocele, a prolapse, or an intussusception may all become visible only on straining.

Digital rectal examination, described in Chapter 5, should assess resting tone, squeeze pressure, and the coordination of the pelvic floor on straining. Ask the patient to bear down during the

examination. In a normal pattern, the puborectalis relaxes, and the anal canal opens. In dyssynergia, the muscle tightens instead. This paradoxical tightening can often be felt directly by the examining finger.

A bimanual examination, with one finger in the rectum and one in the vagina, is especially useful in a woman with suspected rectocele. Ask the patient to strain during this examination. A rectocele is felt as a bulge of the front rectal wall into the examining vaginal finger. This same bimanual technique, performed with the patient straining, is also the key examination for a retroverted uterus, described fully in Chapter 17.

Assess for any degree of rectal prolapse or intussusception at the same visit, following the methods described in Chapters 14 and 15.

16.6 Differential Diagnosis

Several conditions overlap closely with obstructed defecation syndrome. Careful assessment separates them.

Rectal intussusception — described fully in Chapter 15. It often coexists with a rectocele, rather than replacing it as the sole cause.

Rectal prolapse — described in Chapter 14. A full-thickness prolapse can itself cause symptoms of obstructed defecation.

Slow transit constipation — a whole-colon problem, rather than a rectal outlet problem. The two can coexist, and investigations, described below, help distinguish them.

Retroverted uterus — covered fully in Chapter 17. This cause is specific to women, and is often missed unless specifically examined for.

Anal stenosis — described in Chapter 18. A narrowed anal canal can also cause difficulty with evacuation, though the mechanism is different from a true outlet obstruction.

A careful history and a thorough bimanual examination usually narrow this list considerably, before any investigation is ordered.

16.7 Investigations

Defecography, described in Chapter 8, is the key investigation for obstructed defecation syndrome. It shows the rectum, and any rectocele, during active straining and defecation. It also shows whether the rectocele empties completely, or traps contrast material.

MRI defecography is a modern alternative. It avoids radiation exposure. It can also show the bladder, uterus, and other pelvic organs at the same time, which is useful when a retroverted uterus is suspected.

Anorectal manometry, described in Chapter 8, assesses resting and squeeze pressure. It can also test for a normal relaxation response during simulated straining, which helps confirm or exclude dyssynergia.

A balloon expulsion test is a simple, useful screening test for dyssynergia. A balloon is placed in the rectum, and the patient is asked to expel it. Difficulty expelling the balloon, despite normal pressures elsewhere, suggests a coordination problem rather than a structural blockage.

Colonoscopy is advisable in an older patient, or in any patient with red flag symptoms, to exclude another cause of the symptoms.

16.8 Principles of Management

Correctly identifying the cause matters more than any single treatment. A structural rectocele needs a structural repair. Dyssynergia needs retraining, not surgery. Treating the wrong cause disappoints the patient, and rarely helps.

Conservative treatment is the correct first step in almost every patient, regardless of the underlying cause. This includes dietary fibre, adequate fluid intake, and correcting the habit of excessive straining.

Pelvic floor physiotherapy, including biofeedback training, is the primary treatment for dyssynergia. It is highly effective in a well-motivated patient. Surgery has no useful role in dyssynergia alone.

Surgery is considered for a symptomatic rectocele that clearly correlates with the patient's symptoms, once conservative treatment has been tried and has failed.

16.9 Surgical Techniques for Rectocele

Transvaginal repair — the rectocele is approached and repaired through the vagina. This is a well-established approach, often performed jointly with, or by, a gynaecologist.

Transanal repair — the rectocele is approached and repaired through the anal canal. This avoids a vaginal incision, and suits a colorectal surgeon's usual approach.

Transperineal repair — the rectocele is approached through the perineum, between the vagina and the anus. This approach also allows repair of the perineal body at the same time, if it is weakened.

Stapled trans-anal rectal resection, known as the STARR procedure — a circular stapling device removes a strip of the redundant, prolapsing rectal wall, correcting both a rectocele and a coexisting intussusception in the same operation.

Ventral mesh rectopexy, described in Chapter 14, is used when intussusception is the dominant finding, with or without a coexisting rectocele.

No single technique suits every patient. The choice depends on the size and position of the rectocele, whether intussusception coexists, and the surgeon's own training and experience.

16.10 Special Situations

Rectocele with coexisting dyssynergia — needs pelvic floor physiotherapy first, even when a rectocele is present. Surgery on the rectocele alone often disappoints, if the dyssynergia is not also addressed.

Rectocele with rectal intussusception — needs assessment of both findings together, following the approach in Chapter 15. A single operation, such as the STARR procedure, may address both at once.

Suspected retroverted uterus — needs the specific bimanual assessment described in Chapter 17. Do not assume a rectocele is the sole cause of symptoms in a woman, without considering this possibility.

Young patient with mild symptoms — conservative treatment and pelvic floor therapy should be tried thoroughly, and for a reasonable period, before any surgery is considered.

Recurrent symptoms after surgery — needs careful reassessment. A missed functional component, such as dyssynergia, is a common reason for a disappointing surgical result.

16.11 Complications of Treatment

Conservative treatment and biofeedback carry very little risk. The risks below apply mainly to surgery.

Persistent symptoms, if a coexisting functional cause, such as dyssynergia, was not identified or treated.

Dyspareunia, or pain during intercourse, particularly after a transvaginal repair.

Bleeding or infection at the operative site.

Recurrence of the rectocele over time.

Anal stenosis, described in Chapter 18, as a rare complication of stapled procedures such as STARR.

16.12 Common Mistakes to Avoid

Offering surgery for a rectocele found on imaging, without confirming it is the true cause of the patient's symptoms.

Missing dyssynergia, and proceeding straight to surgery, when biofeedback would have served the patient better.

Failing to ask directly about digital splinting, out of a mistaken sense that the patient will volunteer this detail unprompted.

Missing a retroverted uterus as a contributing cause, in a woman with unexplained obstructed defecation.

Treating a small, asymptomatic rectocele found incidentally on imaging, when it is not the cause of the patient's complaint.

16.13 Recording and Follow-Up

Record the suspected cause, the key examination findings, and the treatment plan chosen. For example: "Obstructed defecation syndrome, rectocele 3 cm on bimanual examination, digital splinting present. Plan: pelvic floor physiotherapy, defecography to confirm, review in 8 weeks." Arrange a follow-up visit to check symptom response before considering any surgical referral.

16.14 Why This Chapter Matters

Obstructed defecation syndrome is easy to misdiagnose, and easy to mistreat, if its cause is not correctly identified first. A careful history, a thorough bimanual examination, and the right investigation together point to the true cause, whether structural or functional. The next chapter turns to a specific, often overlooked cause in women: a retroverted uterus, and its relation to obstructed defecation.