KIDNEY STONES - A PRIMER

What is a kidney stone?

It is a crystalline structure that forms in the kidney from an excess amount of minerals salts that are present in the urine.  They vary in size from 1 to 2 millimeters up to 30 - 40 millimeters.  There are five major types of kidney stones:  calcium oxalate (most common), calcium phosphate, uric acid (seen in gout patients), struvite (from chronic urinary infections) and cystine (inherited type).

What causes kidney stones?

Kidney stones occur in 10% of the U.S. population with the geographical Southeast having the highest incidence.  Hot, arid climates and reduced water consumption are the most common risk factors.  Other causes include increased salt intake, increased consumption of calcium and oxalate-rich food, such as rhubarb, spinach and nuts, high protein diets and sedentary jobs.

Specific medical disorders that lead to stone formation include:  gout; hyperparathyroidism, an excess hormone secretion that results in high calcium levels; and low urinary citrate.  Citrate is a natural inhibitor of stone formation. 

When do kidney stones require medical treatment?

 Kidney stones require immediate treatment when they cause obstruction of the urinary tract.  This is commonly seen when the stone migrates from the kidney into the ureter, the tube that drains the kidney to the bladder.  Stones located in the kidney are usually asymptomatic and can be treated electively when they reach a size of 5 millimeters or more. 

What treatments are used?

For stones in the kidney that are less than 2 millimeters, a shock-wave lithotripsy can be used to fragment the stone and allow it to pass.  For larger stones, the kidney can be percutaneously entered from the back of the kidney to fragment and remove the stone.  For stones in the ureter, either a small scope can be inserted through the bladder into the ureter and a laser can be utilized to break the stone or a less invasive ESWL.

Can kidney stones be prevented?

They can be prevented using dietary modifications.  These include:  increasing water intake, reducing salt intake and limiting calcium and oxalate consumption.  For uric acid stone formers, limiting protein rich foods will help prevent development.  Other medical therapies include:  thiazide diuretics (to reduce calcium excretion), potassium citrate (to increase urinary citrate) and Allopurinal (a drug that blocks uric acid formation).