Sometimes bladder stones — even large ones — cause no problems. But if a stone irritates the bladder wall or blocks the flow of urine, signs and symptoms may include:

• Lower abdominal pain
• In men, pain or discomfort in the penis or testicles
• A burning sensation during urination
• Frequent urination
• Difficulty urinating or interrupted urine flow
• Blood in the urine
• Cloudy or abnormally dark-colored urine

Bladder stones usually develop when your bladder doesn't empty completely, and the urine forms crystals. Some infections can lead to bladder stones, and sometimes an underlying condition that affects the bladder's ability to hold, store or eliminate urine can result in bladder stone formation. Any foreign materials present in the bladder tend to cause bladder stones.

The most common conditions that cause bladder stones include:

• Prostate gland enlargement. An enlarged prostate (benign prostatic hyperplasia) can cause bladder stones in men. The enlarged prostate can obstruct the flow of urine, preventing complete emptying of the bladder.
• Damaged nerves (neurogenic bladder). Normally, nerves carry messages from your brain to your bladder muscles, directing your bladder muscles to tighten or release. If these nerves are damaged — from a stroke, spinal cord injury or other health problem — your bladder may not empty completely.

Other possible causes of bladder stones include:

• Inflammation. Bladder inflammation, sometimes caused by urinary tract infections or radiation therapy to the pelvis, can lead to bladder stones.
• Medical devices. Bladder catheters — slender tubes inserted through the urethra to help urine drain from your bladder — may cause bladder stones. So can objects that accidentally migrate to your bladder, such as a contraceptive device or urinary stent. Mineral crystals, which later become stones, tend to form on the surface of these devices.
• Kidney stones. Stones that form in your kidneys are not the same as bladder stones. They develop in different ways. But small kidney stones may travel down the ureters into your bladder and, if not expelled, can grow into bladder stones.

Bladder stones are common in children in developing countries — often because of dehydration, infection, abnormalities in the urinary tract and a low-protein diet. In other parts of the world, bladder stones occur primarily in adults.

Conditions that raise the risk of bladder stones include:

• Bladder outlet obstruction. Any condition that blocks the flow of urine from your bladder to the urethra — the tube that carries urine out of your body — can lead to bladder stone formation. Bladder outlet obstruction has many causes, but the most common is an enlarged prostate.
• Neurogenic bladder. Stroke, spinal cord injuries, Parkinson's disease, diabetes, a herniated disk and a number of other problems can damage the nerves that control bladder function. Some people with neurogenic bladder may also have an enlarged prostate or other type of bladder outlet obstruction, which further increases the risk of stones.

Bladder stones that aren't expelled — even those that don't cause symptoms — can lead to complications, such as:

• Chronic bladder dysfunction. Untreated bladder stones can cause long-term urinary problems, such as pain or frequent urination. Bladder stones can also lodge in the opening where urine exits the bladder into the urethra and block urine passage.
• Urinary tract infections. Recurring bacterial infections in your urinary tract may be caused by bladder stones.