ESSENTIALS OF DIAGNOSIS

• Inability to voluntarily evacuate rectal contents.

• Normal colonic transit time.

General Considerations

Obstructed defecation may result from anal stenosis, pelvic floor dysfunction, or abnormal rectal fixation. The most common cause of anal stenosis is scarring after anal surgery, in particular, inexpertly performed hemorrhoidectomies. Other causes include anal tumors, Crohn’s disease, radiation injury, recurrent anal ulcers, infection, and trauma.

Pelvic floor dysfunction, alternatively referred to as nonrelaxing puborectalis syndrome, anismus, or paradoxical pelvic floor contraction, is a functional disorder in which the neuromuscular function of the pelvic floor and anus is normal but voluntary control is dysfunctional.

In health, the puborectalis is contracted “at rest” maintaining the anorectal angle. During defecation, the muscle relaxes and evacuation occurs. In nonrelaxing puborectalis syndrome the patient does not relax the puborectalis and instead maintains or increases (paradoxical contraction) the anorectal angle. Thus, the patient performs a Valsalva maneuver against an obstructed outlet and elimination does not occur or is significantly diminished.

Patients who chronically strain at stool whether from chronic constipation or pelvic floor dysfunction may develop lengthening of the attachments of the rectum to the sacrum leading to descending perineum syndrome. The increased mobility allows for internal rectal prolapse (intussusception) and in some cases formation of solitary rectal ulcer and rectal procidentia. Intussusception causes outlet obstruction because the upper rectum moves away from the sacrum and telescopes into the more distal rectum.

Clinical Findings

A. Symptoms and Signs

Anal stenosis presents with increasing difficulty with defecation, thin and sometimes painful bowel movements, and bloating. Patients with nonrelaxing puborectalis syndrome similarly complain of straining and anal or pelvic pain, but also complain of constipation, incomplete evacuation, and a need to perform digital maneuvers to evacuate rectal contents. Patients with internal intussusception also complain of constipation, sensations of rectal fullness, or incomplete evacuation, but also note mucous discharge, rectal bleeding, and tenesmus.

Examination of the patient with anal stenosis may reveal postsurgical changes and a stenotic anal canal. Digital examination may be quite painful or impossible. Digital examination of the patient with nonrelaxing puborectalis syndrome may reveal a tender pelvic muscular diaphragm. During the digital examination if the patient is directed to squeeze to mimic holding in flatus, a paradoxical relaxation and Valsalva may occur. Similarly, if the patient is asked to “bear down” to simulate a bowel movement they may paradoxically contract the external sphincters and puborectalis muscles. Digital examination of the patient with internal intussusception may be much the same as that for nonrelaxing puborectalis but with the additional findings of a mass. The mass is the lead point of the intussusceptum. It may be anterior and ulcerated (solitary rectal ulcer) or circumferential. The ulcer is 4-12 cm from the anal verge and is the ischemic traumatized lead point of the internal intussusception. Sigmoidoscopy may reveal the circumferential intussusceptum or an ulcerated mass that appears malignant. Pathologic examination reveals diffuse submucosal cysts with a characteristic fibrosis pattern distinguishing it from colorectal malignancy.

B. Laboratory and Imaging Studies

No additional studies of the patient with anal stenosis are required, but patients with nonrelaxing puborectalis syndrome and internal intussusception should have defecography, colonic transit studies, anorectal manometry with the balloon expulsion test, and barium enema or colonoscopy.

Patients with nonrelaxing puborectalis syndrome or internal intussusception will have a normal colon on barium enema or colonoscopy and normal colonic transit to the rectosigmoid. On balloon expulsion test, they will be unable to expel the balloon.

With nonrelaxing puborectal syndrome, cinedefecography will demonstrate persistent anterior displacement of the rectum on the lateral view and paradoxic contraction of the puborectalis with attempted defecation. In the patient with internal intussusception, defecography will document intussusception.

Differential Diagnosis

Causes of anal pain include a fissure, thrombosed external hemorrhoids, perirectal abscess, malignancy, foreign body, and proctalgia fugax. Proctalgia fugax (levator syndrome), a diagnosis of exclusion, is suggested when a patient complains of pain that awakens him or her from sleep. The pain is generally left-sided, short-lived, and relieved by heat, dilation, or muscle relaxants. The patient often has a history of migraines and may report the occurrence of pain in relation to stressful events.

Other causes of obstructed defecation include fecal impaction, rectal or anal cancer, descending perineum syndrome, and rectocoele.  Fecal impaction may occur as a result of nonrelaxing puborectalis syndrome, and therapy is therefore directed toward that disorder.

Treatment

A. Medical

Mild anal stenosis may be treated successfully with gentle dilation and bulk agents. Nonrelaxing puborectalis syndrome is best treated with biofeedback. The puborectalis is retrained to relax during the act of defecation, which allows the act to proceed without obstruction. Mild to moderate intussusception is treated with bulk agents, modification of bowel habits, and reassurance. The patient is instructed to stimulate a bowel movement in the morning and avoid the urge to defecate the remainder of the day because the fullness they sense is the proximal rectum intussuscepting into the distal rectum. The urge to defecate resolves with time, as does the intussusception.

B. Surgical

Severe anal stenosis is treated surgically if there is no evidence of active disease (ie, Crohn’s disease) and healthy tissue is available to perform the anoplasty. Both procedures involve incision of the stenotic anus, mobilization of the surrounding skin, and advancement of the healthy tissue into the closure relieving the stenosis.

Prognosis

The prognosis for anal stenosis is excellent if there is no evidence of active disease. Patients with nonrelaxing puborectalis have excellent results with biofeedback, but may require retraining. Most patients with mild to moderate intussusception do quite well once they are reassured that an abnormality exists and it is not malignant.

References

Glia A et al: Constipation assessed on the basis of colorectal physiology. Scand J Gastroenterol 1998;33(12):1273.

Mertz H et al: Symptoms and physiology in severe chronic constipation. Am J Gastroenterol 1999;94(1):131.

Nyam DC et al: Long-term results of surgery for chronic constipation [published erratum appears in Dis Colon Rectum 1997 May;40(5):529]. Dis Colon Rectum 1997;40(3):273.

Source: Mark Lane Welton, MD
Portions of this article are reprinted from Way LW, Doherty GM (eds): Current Surgical Diagnosis & Treatment, 11th ed. New York: McGraw-Hill, 2003