Kidney stones, also called renal calculi, are solid concretions (crystal aggregations) of dissolved minerals in urine; calculi typically form inside the kidneys or bladder. The terms nephrolithiasis and urolithiasis refer to the presence of calculi in the kidneys and urinary tract, respectively.

Overview

The kidneys are a pair of organs that are primarily responsible for filtering metabolites and minerals from the circulatory system. These secretions are then passed to the bladder and out of the body as urine. Some of the substances found in urine are able to crystalize, and in a concentrated form these chemicals can precipitate into a solid deposit attached to the kidney walls. These crystals can grow through a process of accretion to form a kidney stone. In medical terminology these deposits are known as renal calculi (Latin renal, "kidney" and calculi, "pebbles").

Renal calculi can vary in size from as small as grains of sand to as large as a golf ball. Kidney stones typically leave the body by passage in the urine stream, and many stones are formed and passed without causing symptoms. If stones grow to sufficient size before passage—on the order of at least 2-3 millimeters—they can cause obstruction of the ureter. The resulting obstruction with dilation or stretching of the upper ureter and renal pelvis as well as spasm of muscle, trying to move the stone, can cause severe episodic pain, most commonly felt in the flank, lower abdomen and groin (a condition called renal colic). Renal colic can be associated with nausea and vomiting due to the embryological association of the kidneys with the intestinal tract. Hematuria (bloody urine) is commonly present due to damage to the lining of the urinary tract.

Within the United States, about 10–15% of adults will be diagnosed with a kidney stone, and the total cost for treating this condition was US$2 billion in 2003. The incidence rate increases to 20–25% in the Middle East, because of increased risk of dehydration in hot climates. (The typical Arabian diet is also 50% lower in calcium and 250% higher in oxalates compared to Western diets, increasing the net risk.) Recurrence rates are estimated at about 10% per year, totalling 50% over a 5–10 year period and 75% over 20 years. Men are affected approximately 4 times more often than women.

History

The existence of kidney stones has been recorded since the beginning of civilization, and lithotomy for the removal of stones is one of the earliest known surgical procedures. In 1901, a stone was discovered in the pelvis of an ancient Egyptian mummy, and was dated to 4,800 BCE. Medical text from ancient Mesopotamia, India, China, Persia, Greece and Rome all mentioned calculous disease. Part of the Hippocratic oath contains an admonition about the dangers of operating on the bladder for stones. The Roman medical treatise De Medicina by Cornelius Celsus contained a description of lithotomy, and this work served as the basis for this procedure up until the 18th century.