I've been told by my NS that constipation, with a ventriculoperitoneal shunt, will cause pressure headaches. Essentially, your body is trying to maintain an equilibrium of pressure, and when you have more stool in your peritoneal area, it increases the pressure in your abdomen, so then the CSF backs up into your ventricles (causing headaches or worse shunt problems) to equalize the pressure. I notice that I get pressure headaches when I'm super backed up, however i've never had shunt failure due to constipation.

In a (possibly related, possibly unrelated) topic, I had a bowel obstruction about 7 years ago. My intestines were covered with scar tissue about an inch thick. I had just had acute appendicitis with a full surgical extraction (not laproscopic). The doctor hypothesized that the scar tissue developed as a response to the CSF draining into that area. Basically he said that CSF is not a naturally-occurring substance in the abdomen and so my body developed scar tissue as a response. My NS said that this was NOT the case and that CSF actually has a very similar composition to the fluids in your abdomen and would not directly cause the formation of the scar tissue. He said it was more likely a response to the appendicitis and debris from the infection. I don't know which (if either) is true, particularly because it seems that my NS is sometimes motivated by saving face and evading blame.

All this is to say that if you have a shunt that drains into your abdomen, it is likely affected by constipation. It'd be nice if someone else could corroborate or refute this with their own experience. I hope this was helpful and i'll be thinking of you and your son and sending him positive recovery and wellness vibes from Minnesota!