Obstructed Defecation

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.