Anal investigations

Anorectal manometry

• Measures pressures generated by anal sphincter muscles, sensation in the rectum, and the neural reflexes that area needed for normal bowel function
• Detects functional sphincter weakness
• Detects abnormal sensation
• Decreased resting pressure - isolated internal sphincter dysfunction (normal 40-80mmHg)
• Decreased squeeze pressure - isolated external sphincter dysfunction
• Performed via intra-anal transducer (can be balloon catheter, water perfused tube catheter, or solid state micro-transducer)

Balloon expulsion test

• Evaluates the ability to expel a balloon inflated to 50-60mL, simulating stool

Electromyography

• Records the change from basal electrical activity of motor units of the external sphincter and puborectalis during activity
• Patients with inappropriate or paradoxical puborectalis contraction fail to show a relaxation of the muscles when asked to push

Endorectal US

• Structural abnormalities of anal sphincters, rectal wall, puborectalis muscle
• USS is better for internal sphincter, while MRI is better for external sphincter
• Can be used to delineate complex fistula anatomy

Defecography

• Dynamic study of the anorectum and pelvic floor during defecation
• Barium defecography is generally done at Austin, but MRI is also available (gives more information on soft tissue)
• Enterocoele
• Rectocoele
• Rectal prolapse
• Cul-de-sac hernia
• Also provides information on functional aspects such as non-relaxation of puborectalis and degree of rectal emptying
• Anal sphincter length, anorectal angle, pelvic descent

Pudendal nerve terminal motor latency

• Measures conduction of the pudendal nerve from its emergence at ischial spine to the internal anal sphincter, by the use of a transducer
• Normal times are 2.0 +/- 0.2ms
• Prolonged values seen in traumatic injuries, chronic stretch injury, sacral nerve root damage or chronic disease
• Not used routinely