How does a high-pressure neurogenic bladder cause problems?
It can cause urine leakage and kidney damage.
Figure 1 represents a normal bladder. The wall of the bladder is yellow, the inner lining of the bladder (mucosa) is pink and the urine is gold.
A normal, thin-walled bladder can expand easily with little change in pressure. The urine is shown in gold and the bladder muscle in yellow. A nearly empty bladder (on the left) can expand easily to accommodate the extra volume as it fills. Because it can expand, a full bladder (on the right) will still have a pressure of nearly zero. This low pressure is important because it prevents leakage, and it protects the kidneys from high pressure.
Add urine volume
No change in bladder pressure
A high-pressure bladder will not expand very well when urine is added to the bladder. Its thick walls will resist stretching. Instead, the added volume will cause a rise in pressure in the bladder. This added pressure will be relieved in one of two ways. Either the urine will back up into one or both kidneys, or the urine will leak out the urethra (incontinence).
Pressure rises because bladder can't stretch
Add urine volume
When elevated pressures back up into the kidney over a long period of time (months to years), hydronephrosis will develop. Hydronephrosis literally translates to “water swelling of the kidney." Here it is shown on just one side (right) for comparison. However, it can happen on both sides. Hydronephrosis can persist even when the bladder is empty. The swelling of the ureters leads to loss of the 'meat' of the kidney. This eventually leads to kidney failure.
It can cause bladder infections (also known as urinary tract infections, or "UTIs")
Many people who have a neurogenic bladder use a catheter to empty their bladder. This leads to bacteria growing in the urine. This is not necessarily a bladder infection; the bacteria are just living in the urine. You don’t experience symptoms of an infection unless the bacteria invade the wall of the bladder. As long as the person empties their bladder regularly, the number of bacteria in the bladder will be frequently reduced to very low numbers, and no infection will result. Here you see a bladder with several bacteria (in green).
For more on the difference between bacteria in the urine and a true bladder infection, watch this video by Dr. Elliott.
Here we see that when the bladder is emptied, most of the bacteria are emptied out with the urine. By keeping the number of bacteria in the urine low by frequent catheterization, infections are prevented.
When the bladder pressure is elevated by the thick-walled bladder that doesn't stretch well, that acts like a “pressure cooker” for the bacteria. The pressure pushes the bacteria into the wall of the bladder and into the meat of the kidney, and eventually the bloodstream. This invasion of bacteria from the urine (where is it harmless) into the actual tissues of the body (where it causes damage) is what leads to the symptoms of a urinary tract infection.
We have three main methods to lower the bladder pressures to help prevent kidney damage, bladder infections and incontinence. These are medication pills, Botox injections, and bladder enlargement surgery. Because these treatments relax the bladder muscle, they are almost always combined with self-catheterization 4-6 times a day to empty the bladder.
Pills such as oxybutynin or tolterodine are known as anticholinergic medications. They are taken by mouth 1 to 4 times a day. They are absorbed in the stomach and work in the bladder to relax the bladder muscle. Side effects can include dry eyes, dry mouth and constipation. These are usually what we try first.
Botox injections are performed using a small scope/camera through the urethra (Figure 8). The procedure only takes 5-10 minutes and can be done awake in the office. We inject the Botox into about 10-20 different spots in the bladder muscle. The medication lasts about 6 months and then can be repeated. Most insurance companies require that we try several pills first before they will pay for Botox.
When pills and Botox don’t work, bladder enlargement surgery (a.k.a., bladder augmentation) is the best option. This works even in the worst-case scenarios. The bladder is opened in the middle like a clamshell and then a segment of intestine is added to the top of it. This more than doubles the volume of the bladder; and, because the intestine is much more flexible than the diseased bladder, the pressures in the bladder drop dramatically.