Methods of Evaluation of Anorectal Causes of Obstructed Defecation

Abstract

Obstructed defecation is a complex disorder that results in impaired propagation of stool from the rectum. It is one of the major subtypes of functional constipation and can be secondary to either functional or anatomic etiologies. Patients with obstructed defecation typically present with symptoms of abdominal discomfort, a sensation of incomplete evacuation and rectal obstruction, passage of hard stools, the need for rectal or vaginal digitation, excessive straining, and reduced stool frequency. Evaluation of obstructed defecation is multimodal, starting with a thorough history and physical examination with focus on the abdominal, perineal, and rectal examination. Additional modalities to elicit the diagnosis of obstructed defecation include proctoscopy, colonic transit time studies, anorectal manometry, a rectal balloon expulsion test, defecography, electromyography, and ultrasound. The results from these studies should be taken in the context of each patient's clinical situation, as there is no single criterion standard for the diagnosis of obstructed defecation. Surgery is typically a last resort for these patients and the majority of patients will have good symptomatic management with diet and lifestyle changes. Patients who are found to have functional mechanisms behind their obstructed defecation also benefit from pelvic floor exercises and biofeedback therapy.

Keywords: anorectal manometry; colonic transit time; defecography; diagnosis; diagnostics; digital rectal examination; electromyography; functional constipation; obstructed defecation; proctoscopy; rectal balloon expulsion; ultrasound.

Fig. 1

Sitzmark test at day 10 in a patient with colonic inertia. Retained markers are distributed throughout the colon. In a normal patient, greater than 80% of markers are evacuated prior to imaging. An abnormal study is defined as retention of 20% or more markers beyond day 4, corresponding to 5 markers in a typical test. In obstructed defecation, retained markers will collect in the rectum or rectosigmoid. (Photo credit: A. S. Kumar, MD.)

Fig. 2

Anorectal manometry. Normal tracing of resting tone during a pull-through maneuver. Note that the pressure measurement progressively increases from the 4 cm level to 2 cm level and that a small decrease in pressure occurs at the 1-cm level as well as a precipitous drop to zero as the probe exits the anal canal. (Photo credit: Lee E. Smith.)

Fig. 3

Anorectal manometry—Rectoanal inhibitory reflex (RAIR). Each spike (thin arrow) corresponds with insufflation of the rectal balloon. (A) Normal RAIR waveform. Relaxation of the internal sphincter occurs following balloon insufflation (thick arrow). (B) Absence of RAIR in Hirschsprung disease. No RAIR follows insufflation of the rectal balloon. (Photo credit: Adapted with permission from Dr. Lee E. Smith).

Fig. 4

Anorectal manometry—strain maneuver. (A) Normal. Relaxation of the sphincter during the strain maneuver. (B) Anismus. Paradoxical increase (arrow) in sphincter pressure during the strain maneuver (Photo credit: Adapted with permission from Dr. Lee E. Smith).

Fig. 5

Electromyography. (A) Normal activity of the puborectalis muscle at rest and during coughing, squeezing, and straining. (B) Paradoxical increase of activity during straining in a patient with paradoxical puborectalis contraction (arrow). (Photo credit: Adapted with permission from Dr. Lee E. Smith).

Fig. 6

Defecography. R is the rectum; A is the margin of the distal anus. (1) The rectum at rest. (2) The rectum during voluntary squeeze. The arrow indicates the angle created (depicted in white) by the puborectalis muscle pull. (3) The rectum during evacuation. The anorectal angle (depicted in white) opens as the puborectalis muscle relaxes. (Photo credit: Adapted with permission from Dr. Lee E. Smith).

Fig. 7

Defecography. (A) Enterocele. V marks the vagina. E marks the enterocele as it descends between the vagina and rectum. (B) Rectocele. R marks the rectocele. A marks the margin of the distal anus. (C1 and C2) Intussusception of the rectum. Note the progressive infolding of the rectum. (Photo credit: Lee E. Smith and Anjali Kumar.)