Why do we grow stones in the urinary tract?

Stones disease of the urinary tract

Stone disease or urolithiasis is surpassed only by prostatic disease when we look at the total urology workload. Stones can occur in all parts of the urinary tract, including the pelvicalyceal system of the kidney, the ureter, the bladder and occasionally in the urethra. Symptoms are often provoked because of an obstruction or from a result of urinary tract infections.

During the last 150 years we have seen a change in the pattern of stone incidence. Bladder stones which were once extremely common, particularly in children, and were one of the few conditions successfully treated by surgery before the advent of anaesthesia and antisepsis, are now much less common than ureteral and kidney stones. Lithotomy or 'cutting for stone', was often performed by specialist surgeons who travelled up and down the country. They used a perineal approach to the bladder, placing the patient in the lithotomy position. A bladder sound (curved bougie) was placed via the urethra into the bladder to locate the stone.

A captivated audience was often needed to hold down the unfortunate patient for the surgeon’s theatrical intervention. The operation was often completed in seconds. Nowadays, upper tract calculi are much more common than bladder calculi and the incidence is rising.

The stones range from the uncommon staghorn calculus (7 % of stones), which fill the complete pelvicalyceal system, to small stones developing in the pelvicalyceal system that may migrate and obstruct the ureter. Acute ureteric obstruction causes severe pain and presents as the surgical emergency known as ureteric colic. Most stone disease is, however, asymptomatic or otherwise presents non-urgently in an outpatient clinic.

In developed countries stone disease in childhood is now rare. Peak incidence of stone disease is in early adulthood and declines slowly thereafter. Males are affected two and a half times more often than females. Unfortunately, there is a high incidence of recurrent stones.

The formation of urinary stones

Generally and on a global scale, urinary stone incidence is increasing. This has been put down to four major reasons; dehydration (due to the lack of safe drinking water in many developing countries); an unbalanced diet high in protein and salt; a more sedentary life style and obesity. In most people urine contains certain chemicals that prevent crystals from forming. At times, certain materials may become concentrated in the urine and form solid crystals. These crystals can lead to the development of stones when materials continue to build up around them, similar to how a pearl is formed in an oyster. The incidence of urolithiasis, or stone disease, is around 12 % by the age of  70 for males and 5-6 % for females in the United States. The majority of stones contain calcium, with most being comprised of a material called calcium oxalate. Other types of stones include substances such as calcium phosphate, uric acid, cystine and struvite.

A number of risk factors play major roles in stone formation. The first is loss of body fluids (dehydration). When one does not consume enough fluids during the day, the urine often becomes quite concentrated and darker.

This increases the chance that crystals can form from materials within the urine, because there is less fluid available to dissolve them. Diet can also affect the probability of stone formation. A high-protein diet can cause the acid content in the body to increase. This decreases the amount of urinary citrate, a good chemical that helps prevent stones. As a result, stones are more likely to form. A high-salt diet is another risk factor, as an increased amount of sodium passing into the urine can also pull calcium along with it. The net result is an increased calcium level in the urine, which increases the probability for stones. Intake of oxalate-rich foods such as leafy green vegetables, nuts, tea or chocolate may also worsen the situation. Certain bowel conditions can also increase the risk such as chronic diarrhea, Crohn‘s disease, and gastric bypass surgery. Obesity is also an independent risk factor for stone formation. Finally, a family history of stones, especially in a first-degree relative (parent or sibling), dramatically increases the probability of having stones.

Stone types

In most cases analysing stones will contribute with the further management of the patient. If this is not possible however, the chemical nature of the stone can often be inferred from the radiological findings. The stone types most commonly encountered are calcium oxalate (>80 %), with urate stones being the next most common, followed by struvite and the rare cystine stone.

Calcium-containing stones

Four out of every five urinary stones are calcium stones. These stones are normally a mixture of calcium and oxalate, and less so calcium and phosphate or a combination of all three. The most common is calcium oxalate. Most patients who suffer from calcium stones have a condition called hypercalciuria, or too much calcium in the urine. This may be because the patients absorb too much calcium from the intestines or from their bones. Extensive research has shown that most of these stones are developed because of additional dietary factors. A high protein diet, high salt intake and vitamin D, and a low fluid intake are major factors existing in patients with regard to these stones. Calcium stones and especially calcium oxalate stones are often the hardest and most difficult to fragment. This is where the Swiss LithoClast® Master is most useful as its three-way energy system breaks, fragments and evacuates even the hardest of calculi.

Uric acid stones

Uric acid calculi often form in patients who are dehydrated, have a low intake of f luids, who have a high protein diet and those who suffer from gout. Certain genetic disorders may also contribute to the patients’ risk of developing urinary stones.
Other causes of uric acid stones are myeloproliferative disorders and chemotherapy. The majority of uric acid stones can be treated medically. Treatment involves a high f luid intake to maintain an output of at least 2 l of urine a day and the adjustment of the urinary pH to 6.5-7.0. This can usually be achieved by an oral dose of 1 g of sodium bicarbonate 3-4 times a day. This dose may need to be varied and so it is important to ensure that patients monitor their urine pH with test strips and adjust the dose of bicarbonate accordingly. If increased hydration and adjustment of pH do not achieve dissolution or prevent recurrence, the latter usually due to patient non-compliance, then uric acid excretion can be reduced by specific medication. This regimen should prevent most recurrences.

This may be because the patients absorb too much calcium from the intestines or from their bones. Extensive research has shown that most of these stones are developed because of additional dietary factors. A high protein diet, high salt intake and vitamin D, and a low fluid intake are major factors existing in patients with regard to these stones. Calcium stones and especially calcium oxalate stones are often the hardest and most difficult to fragment. This is where the Swiss LithoClast® Master is most useful as its three-way energy system breaks, fragments and evacuates even the hardest of calculi.

Struvite stones

Struvite stones normally occur after a urinary tract infection or a high alkaline urine. They are more common in females than males. These type of stones are often large in size and are prone to quick growth. They can often develop without any symptoms or warning. Surgical removal of the stone, either by ESWL, percutaneous techniques or open surgery, is usually required although successful dissolution of struvite has been reported.

Cystine stones

Cystinuria disease is an inherited condition that is presented by the formation of cystine stones in the urinary tract. The patient would need two copies of a defective gene, one from each parent, for the condition to be present at birth. It affects 1 in 20’000 people. These patients normally suffer from recurrent episodes of stone formation and their management is multi-modular. Cystine stones make up only 1 % of all stones and deserve mentioning mainly because the correct diagnosis is often delayed. Many patients are subjected to frequent surgical procedures before appropriate preventive measures are initiated. The family history is important as this condition is due to an inherent error in metabolism, which is charact- erised by increased excretion of the amino acids, cystine, ornithine, arginine and lysine.