Under the right conditions, water and minerals combine to create crystals and stones. Towering stone formations called stalactites and stalagmites grow in caves where water drips though mineral-laden rock roofs.  In the human body, crystals and stones can form in urine, which is a combination of water, minerals and other waste products filtered out of the blood by the kidneys.  If the balance between water and mineral concentrations in the urine tips in the wrong direction, or if the urine becomes too acidic, crystals may form from minerals and coalesce into kidney stones. The physical consequences depend on the size and location of the stones.

Location matters

Stones can form anywhere in the kidney’s “collecting system,” which begins with the calyx, a hollow chamber emerging from the middle of the organ. Urine made by each of your two kidneys fills its calyx and then passes into a long, narrow tube called the ureter. Each ureter connects its kidney high in the back of the abdomen, one on the right side of the spine and the other on the left,  to the bladder located , deep in the center of the pelvis below. The bladder is a reservoir where urine is stored until it is released from the body. Symptoms of kidney stones depend on their size and location in the collecting system and on the presence or absence of other problems such as infection.

When confined to the kidney’s calyx, the most common stones, made of calcium, are small and cause no symptoms. But the calyx is also the site where large, branched stones called staghorn calculi can grow and fill the hollow structure, clinging to the kidney tissue and damaging it even to the point of kidney failure. Staghorn calculi are associated with recurrent urinary tract infections caused by bacteria that that cause precipitation of magnesium along with calcium.  Staghorn stones are often found as a result of the patient developing fever, back pain and cloudy painful urination – all symptoms of kidney infection. These elaborately branched stones may encase bacteria and grow to huge size before producing symptoms such as blood in the urine, unless a small portion breaks off and passes into the ureter.

The worst pain: when a stone stretches the ureter

A kidney stone may pass from the calyx and through the ureter unnoticed, but if it stretches and irritates the narrow tube as it moves along the resulting pain is intense and colicky, waxing and waning in spasms – and often described the worst pain someone has ever experienced.  Ureter pain is felt in the back, between the ribcage and pelvis, or sometimes in the groin or in the testicle. Sometimes fever and bloody urine accompany the pain. Once the stone passes out of the ureter to the bladder, pain disappears.

Bladder gravel

In the bladder, the stone may remain or pass out through the urethra with urination, causing pain with or without bleeding. When stones accumulate in the bladder they are something like gravel, irritating the lining and precipitating frequent need to urinate, burning urination, bloody urine and low pelvic pain. They may also lower the threshold for bladder infections as bacteria cling to the stones, triggering more stone formation and more symptoms. In medieval times, when clothing was changed infrequently and bathing was a yearly event, bladder infections and stones were so frequent and caused such miserable symptoms that people called stonecutters traveled England’s countryside and cities, peddling the ability to remove bladder stones via an incision between the rectum and the urethra.  There are even reports of people performing the procedure on themselves.

Who gets kidney stones?

Kidney stones are more common in men that women and tend to run in families. Obesity, chronic bladder or kidney infections, inflammatory bowel disease or a history of gastric bypass, surgery, and prior history of stone formation are all risk factors, as are some rare forms of kidney disease and even rarer parathyroid gland tumors. Doctors don’t know exactly why people form stones, but dehydration is almost always a factor in their appearance. When water intake is low the kidney responds by making urine very concentrated and deep yellow. Concentrated urine contributes to the conditions that promote kidney stone formation. Morning urine is much more concentrated than daytime urine because most people do not drink water during the night. Deliberate lack of drinking water during the day in order to avoid the need for bathroom use makes some people such as surgeons and airline pilots particularly prone to kidney stones. People who live in very dry climates or who lose a lot of water through perspiration may have very concentrated urine without realizing that they are chronically dehydrated.

Diet may play a role

Another factor correlated with kidney stone formation is a high protein diet, which increases urine acidity, promoting crystallization of calcium.  High salt diets aggravate the tendency to form stones because as the kidney gets rid of excess sodium, it also pulls calcium into the urine. Curiously, while calcium supplement use may produce kidney stones, calcium from food sources does is not a problem. Rarely, uric acid stones occur in people who have the genetic tendency to gout, or who are taking diuretic hormones.

Treatment

Treatment of kidney stones, like their symptoms, depends on stone size and location. Often, a period of pain control and hydration is often enough to get the patient through the acute problem. If not, the stone can be retrieved from the bladder through a cystoscope passed in through the urethra. A ureter can also be dilated through the scope to remove a stone stuck there. Another technique, called lithotripsy, employs ultrasonic waves applied externally to bombard and shatter stones, rendering them small enough to pass out of the body.

Followup

Beyond the acute phase of treatment, patients who have passed stones need evaluation for conditions like gout, urinary tract infection, and problems with calcium metabolism. Analysis of the stone’s composition can help, especially if it is not the common calcium type. Staghorn stones require more aggressive measures, possibly including open surgical removal.

Anyone who has suffered through the life of a kidney stone needs to be vigilant about drinking water, enough to keep urine very light in color at all times. Weight loss if appropriate, decreasing dietary salt and protein from animal sources, and avoiding calcium and Vitamin D supplements are all helpful in prevention of further stones. Sunlight is a safer source of Vitamin D in those at risk for kidney stones.