When crystals in the urine form into a mass, the mass is known as a calculus or stone, and if a calculus forms within the bladder, it is referred to as a bladder stone. In many cases, a person can have a bladder stone and not have any symptoms, but sometimes it can cause pain or lead to blood in the urine.
How do bladder stones form?
The bladder is a balloon-like organ in your pelvic area, and its function is to store urine from the kidneys. The two kidneys are like filters, removing waste products from your blood. They mix these waste products with water, creating urine, which passes through a pair of tubes, known as the ureters, to the bladder. The urine stays in the bladder until you feel the urge to urinate, and then it is released through a tube called the urethra.
One of the waste products removed from the blood is urea, and when urea stays in your bladder for too long, it begins to join together, forming crystals. After a while these crystals begin to harden and form calculi, or bladder stones. (If the calculi form in the kidneys, they are known as kidney stones.)
How common are bladder stones?
In the UK, bladder stones are not common, but even so, each year about 6,000 people in England go into hospital for treatment related to bladder stones. The majority of bladder stones are found in men over 50 years old due to prostate enlargement. Only 20 to 40 cases a year are in children.
What are the causes that can lead to the formation of a bladder stone?
The most likely cause for a bladder stone developing is not being able to completely empty your bladder, so some urine remains in your bladder after urination. There are several reasons why a person may have trouble emptying their bladder:
- Prostate enlargement - In men, a small gland between the penis and the bladder is known as the prostate. It surrounds the urethra. The prostate helps produce semen, but as men age, the prostate often gets larger, putting pressure on the urethra. One in three men over the age of 50 have an interruption of their normal flow of urine due to an enlarged prostate.
- Cystocele - In women, the bladder can become weak and drop down on to the vagina, affecting the normal flow of urination as it leaves the bladder; excessive straining, such as during childbirth, from chronic constipation or due to heavy lifting can lead to a cystocele.
- Bladder diverticula - Pouches known as diverticula can form on the wall of the bladder, and if they grow too large, they can make it difficult to empty the bladder fully; these pouches can be a result of an infection or enlarged prostate, or they may simply be there from birth.
- Neurogenic bladder - In this condition, the person cannot empty their bladder fully because the nerves that control the bladder are not working properly. People who have this condition usually have some type of spinal cord injury or they have damage to their nervous system caused by a disease such as spina bifida or motor neurone disease. About 10% of people with neurogenic bladder will develop bladder stones.
- Bladder augmentation surgery - One type of treatment for incontinence is to enlarge the bladder by using a piece of bowel to make it larger; around 5% of people who have this type of surgery will develop bladder stones.
- Diet - Though not a common cause of bladder stones in the UK, in developing countries diets high in fat, salt and sugar and low in vitamins A and B increase the risk of developing bladder stones.