The most common cause of voiding problems in children is rectal retention of stool

Voiding problems such as urgency, frequency, accidents, and incomplete emptying are common in children.

In a recent post, I reviewed the Physician’s Guide to MOP — an enema program to treat rectal retention of stool:

Rectal retention of stool

A few years ago, I took care of a child who presented to the hospital in urinary retention and renal failure. He had an advanced case of non-neurogenic neurogenic bladder, also called Hinman’s syndrome. After a few days of Foley catheter drainage, he improved and was able to be discharged home. He was voiding but he was not emptying his bladder completely. His residuals were around 200-300 ml. We tried everything possible: urotherapy, tamsulosin, biofeedback, and botox of the urinary sphincter, but he persisted having high residuals. As a last resort, before proceeding with a Mitrofanoff procedure, I recommended MOP: 1 month later his residual was under 100 ml.

In this post, I will go over what I tell families with regards to the why of MOP.


The function of the rectum

The small and large bowel have very different functions. The small bowel is in charge of absorbing nutrients. The large bowel processes and packages the left-overs from the small bowel. The entire small and large bowel lack sensation: if we could get inside a person and cut with scissors their small or large bowel, they would not feel a thing.

The end of the large bowel is called the rectum. The rectum is very different from the rest of the bowel as it has lots of nerve endings and sensation. A normal person can feel and tell apart gas, liquid, or hard stool in their rectums. The function of the rectum is to sense stool and then alert the brain about the need to eliminate. Although the rectum can store some stool while you find a bathroom, its function is not to store stool.

After children are potty trained, they gain the ability to void and stool when they want. In a world of Ipads, Netflix, YouTube, rigid schedules, etc, children’s attention is constantly onto something. When nature — ie, the rectum — calls them, they have to decide in bewtween YouTube or their rectum. Most times they chose to keep doing what they are doing, gradually strechning the size of the rectum, and gradually becoming numb to  the rectum calls for attention. Eventually, the rectum becomes a storage organ and not a sensing organ, and the child is able to walk around like if nothing is happening with a rectum filled with a ridicoulsly large amount of stool:


The case for MOP

For many years, I tried to treat this problem with oral laxatives. First, I was prescribing Miralax and it was not working. Families complained their children would not take it and that it was impossible to find the right amount to give.

Subsequently, I started recommending bowel cleanouts before starting the daily Miralax. I told the families to give 1 full bottle of Miralax in 1 quart of Gatorade over a morning, during the weekend. If drinking 1 capful of Miralax in one glass of water was hard for most children, imagine 1 bottle of Miralax in 1 quart of Gatorade! The main issue with the Miralax approach was that even if the rectum could be cleaned out for a few days, it was already stretched and numb, resuming its poop storage function after a few days.

Miralax given by mouth in someone with rectal retention of stool tends to cause diarrhea, as the liquid stool goes around the impacted stool.

With MOP the treatment is delivered to the area that most needs it and it is effective immediately. The bowel movement happens right then so the family does not have to worry about when is the Miralax or Ex-lax going to kick in and whether that would be during the recital, soccer game, or winter concert.

MOP is simple to understand and simple to implement.



The most common cause of voiding problems in children is rectal retention of stool. The easiest and most effective way of taking care of rectal retention is with MOP.

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