Calculus, urinary tract
A stone in the ureters, bladder or kidneys that is formed from crystallised substances in the urine.
Types and causes
Kidney and ureteral stones
The majority of stones that form in the ureters and kidneys are composed of calcium oxalate or other salts crystallised from the urine. This stones are sometimes associated with a diet that is rich in oxalates (which can be found, for example in tea and leafy vegetables): high levels of calcium in the blood due to hyperparathyroidism (over-activity of the parathyroid glands); or chronic dehydration.
Other types of uretral or kidney stone are associated with certain cancers and gout. Stones that develop in these locations due to chronic urinary tract infection are termed infective. Kidney stones that fill the entire network of urine-collecting ducts at the top of the ureter are called staghorn calculi, this is due to their shape.
In third world, or developing countries, bladder stones usually form as a result of dietary deficiencies. In more developed countries, they are often caused by an obstruction to urine flow from the bladder and/or a longstanding urinary tract infection. The composition of the stones is related to the alkalinity or acidity of the urine
The most widespread symptom of a stone in the ureter or kidney is renal colic, an extreme pain under the ribs, in the back, that usually spreads into the groin. This pain can be accompanied by vomiting and nausea. There can also be haematuria (blood in the urine). A bladder stone generally causes pain and difficulty when passing urine.
Diagnosis and treatment
Investigation of a suspected calculus typically starts with microscopic examination of the urine, which can show the presence of crystals and red blood cells. The degree of alkalinity or acidity of the urine can reflect the type of stone involved. The location of a stone can often be confirmed by a plain x-ray, although CT scanning or ultrasound scanning can also be used.
Renal colic is treated with analgesic drugs and bed rest. With adequate fluid intake, smaller stones are usually passed in the urine without creating any problems. The first line of treatment for larger stones in the urinary tract is usually ESWL (extracorporeal shock-wave lithotripsy, a procedure that uses ultrasonic waves or shock waves to disintegrate the stones. Alternatively, cytoscopy can be used to crush and remove stone in the lower ureter and bladder. Occasionally in some cases, surgery may be needed to remove the stones.