Stones (Calculi)

Stones in the kidneys, and elsewhere in the urinary system, form when substances normally dissolved in the urine, such as uric acid or minerals, precipitate out of solution. The precipitated substances condense on a tiny centre, such asa speck of protein or a bacterium, and then gradually form a stone as more material collects and clings to it. Why stones form in some people and not in others is not clearly under. stood. One cause may be an imbalance in metabolism which causes excessive amounts of a substance to be produced and excreted. There is a limit to how much of a substance can be dissolved, and once the limit is exceeded the substance will precipitate. An obstruction in the urinary tract which interferes with the flow of urine, prolonged immobility or an infection may also cause stones to form Stones vary in their composition, shape, size and colour. calcium oxalate and calcium phosphate stones are the commonest, uric acid stones less common.

Symptoms

Once formed, stones increase steadily in size. When they pass from the kidney into the ureter they can cause a dull, aching pain in the loin that is made worse by activity, although in some cases pain is slight or absent. Sometimes a kidney stone passing down the ureter causes renal colic, one of the most severe pains the body can experience. Waves of pain start in the loin and radiate round to the navel, or if the stone has reached the lower end of the ureter the pain passes down to the groin. About seventy per cent of stones pass into the bladder and out through the urethra The remainder, however, because of their size or shape, become lodged.

Treatment

Treatment involves relieving the pain with drugs and removing the stone if the pain persists or if the stone is causing obstruction. Sometimes the stone will pass out of the body of its own accord, provided the patient drinks plenty of water. If there is obstruction, due to stones or some other cause, the pressure of urine flow above it will distend the pelvis of the kidney, forming a hydronephrosis If extensive, this will damage the kidney tissue and stop it functioning. If the obstruction occurs lower down the ureter, the ureter itself will distend, as well as the pelvis. forming hydroureter as well as hydronephrosis. Specialist investigation and treatment are then required.