Anorectal Physiology Testing

The shared diagnostic toolkit used to evaluate Rectal Prolapse (Procidentia), Solitary Rectal Ulcer Syndrome (SRUS), Rectocele, Constipation, and pelvic floor disorders generally. Content below is from a textbook reference chapter (Sabiston Ch52 - Pelvic Floor Disorders & Constipation), not primary literature. The chapter refers readers to the ASCRS Consensus Statement of Definitions for Anorectal Physiology Testing and Pelvic Floor Terminology for fuller detail.

Anorectal physiology laboratory tests

Evaluate anal canal pressures to determine anal reflexes, anal sensation, and electromyography recruitment.

• Anorectal manometry — evaluates the high-pressure zone (the length of the anal canal), the resting pressure (mostly due to the internal sphincter), the maximum voluntary pressure and squeeze pressure (due to the external sphincter). Performed by placing a manometry catheter with a water-filled balloon at its tip in the anal canal, with the balloon lying within the rectal lumen. Normal resting pressure: 40–80 mmHg. Also provides information on intrarectal pressures, reflexes, rectal sensation, and rectal compliance; high-resolution manometry can provide greater resolution and minimizes motion artifacts.
• Balloon expulsion test — evaluates the patient’s ability to expel a balloon inflated with 50–60 cc of water/gas/air, simulating stool.
• Pudendal nerve terminal motor latency — measures conduction of the pudendal nerve from its emergence at the ischial spines to the internal anal sphincter, via a transducer. Normal value: 2.0 ± 0.2 ms. Prolonged values are seen in traumatic injuries (spinal cord), stretch injury from obstetric trauma due to prolonged labor, chronic stretch injury (as in long-standing defecation disorders), sacral nerve root damage, or chronic diseases (e.g. diabetes). Typically measured with a special electrode taped to the examiner’s index finger, which stimulates the pudendal nerve while a recording electrode at the base of the finger measures the anal sphincter contraction response.
• Electromyography — records the change in basal electrical activity of motor units of the external sphincter and puborectalis muscle during activity. Patients with inappropriate or paradoxical puborectalis contraction fail to show a relaxation of the muscles when asked to push (relevant to Constipation’s “anismus” subtype).

Imaging to evaluate the pelvic floor and colonic transit

• Endoanal ultrasound — evaluates the integrity, thickness, and possible abnormalities (scars, fistulas) of the internal and external anal sphincter.
• Defecography — a dynamic study of the anorectum and pelvic floor during defecation. Provides information on anatomic abnormalities (rectocele, rectal prolapse, internal rectal intussusception, cul-de-sac hernia) as well as functional disorders (nonrelaxation or paradoxical puborectalis contraction, perineal descent, degree of rectal emptying). Dynamic images captured with fluoroscopy, with the rectum and vagina opacified with radiographic contrast and the patient seated on a radiolucent commode. When performed with MRI (“MRI defecography”), the rectum is opacified with a mixture of ultrasonography gel and gadolinium. MRI’s advantages: high-quality images of pelvic soft tissue/viscera, no ionizing radiation. Its limitation: performed supine, which doesn’t reproduce normal (upright) defecation conditions.
• Colonic transit time — a test of colonic inertia. The patient ingests 24 radio-opaque markers in a capsule (Sitzmarks) and refrains from laxatives/mechanical measures that could interfere with colonic function. Marker progression through three colonic areas (right, left, rectosigmoid) is studied on plain abdominal films taken every other day until day 7. In the healthy population, 80% of markers should be expelled by day 5. Patients with slow-transit constipation or colonic inertia retain a significant portion of markers through the entire study period.

Open items / gaps

• No primary literature yet establishing these tests’ sensitivity/specificity for specific diagnoses — presented here as standard technique descriptions.