Anorectal physiology testing

This is a simple outline of the common anorectal physiology tests that are useful in practice

Patients FAQ

What is anorectal physiology testing?

It is a combination of tests that are designed to look at the function of the anus, colon and rectum (other tests look at the structure).

Why it is done?

Despite the fact that a great deal of information may be gained by expert clinical examination. some elements of function can not be assessed clinically. It provides a reproducible way of accurately measuring certain aspects of function. It can be vital in differentiating the contribution of various defects to disordered function

Where is it done?

I send my patients to GI physiology unit at the Royal London Hospital, where we get excellent service. The unit is one of the best in the country.

Anorectal manometry

There are various ways of measuring anal pressures (balloon catheters, water perfusion catheters and solid state catheters). Pressures are measured along the anal canal during resting and during maximum squeeze at intervals of 1 cm

Anorectal sensation

Measurement of rectal sensation to inflated balloon (minimum perceived volume, defaecation desire volume and maximum tolerable volume), rectal compliance can be calculated if intra rectal pressure is measured and mucosal electro sensitivity can also be measured. Measurement of rectal sensation can be useful in patients with rectal urgency and also in those with megarectum. Gross disturbance of rectal sensation may suggest a poor result following sphincter repairs

Pudendal nerve terminal motor latencies

 

This measures the function of the nerve supply to the sphincter muscles and the pelvic floor (by measuring the speed of transmission in the pudendal nerve (see diagram above). If this becomes prolonged, then it indicates neuropathy of the pudendal nerves and may decrease chance of success following sphincter repairs.

Endoanal ultrasonography

Colonic transit

This is done using either 50 radio opaque markers and getting a plain abdominal x-ray at 100 hours or using radioisotopes. This is useful to document or exclude slow transit constipation. Those with slow transit who may be candidates for surgery need upper GI motility studies as well

Evacuation proctography

This test is a simulation of the process of defaecation. A special synthetic semi-solid stool mixed with contrast is instilled into the rectum, then the patient is seated on a radioluscent commode behind a curtain and asked to defaecate. The test may shed light on a variety of defaecation disorders, revealing internal rectal intussusception, rectocoele, incomplete evacuation and sometimes anismus