Kidney stones or renal calculi are hard crystalline mineral materials formed in kidneys or urinary tract from minerals in urine. These stones are named on the basis of their locations; for example if it is in the kidney it is called nephrolithiasis and likewise if in ureter, ureterolithiasis etc. It is also classified by their chemical compositions like calcium-containing etc. Majority of people with kidney stones are males in the range of 30 and 40 years whereas they tend to occur at a later age in females. Kidney stones are formed when there is decrease in urine volume and/or excess presence of stone-forming substances in urine. People having medical conditions such as gout and those taking certain medications or supplements are at risk for developing kidney stones. Kidney stone formation is also related to dietary and hereditary factors.
Kidney stones are generally eliminated from body through urine. There may be quite a few stones that form and get eliminated from body without any symptoms in an individual but when stones increase in size they start obstructing ureter, which leads to a condition known as postrenal azotemia alogn with ureteral spasms resulting in excruciating pain, generally felt in flank, lower part of abdomen, and groin. This condition is termed as renal colic. This can be associated with symptoms like nausea, vomiting, hematuria, fever, pus in urine, and pain with urination. This condition generally comes episodically and lasts for an hour or so, beginning in flank region and radiating to groin. A confirmatory diagnosis of renal stones is done after a detailed medical history, physical assessment, urine analysis, radiographic tests, ultrasound, and blood draws. If a stone is asymptomatic, then wait-and-watch approach is reasonable. If the stone produces symptoms, then pain relieving medications are given first like nonsteroidal antiinflammatory medications or opiates. In severe cases, surgical intervention may be required, e.g. extracorporeal shock wave lithotripsy in which stones can be fragmented into smaller pieces. In some cases, more invasive type of surgery may be necessary like laser lithotripsy or percutaneous nephrolithotomy. Sometimes, ureteral stent may need to be placed in ureter so as to bypass obstruction and provide symptom relief, and prevention of ureteral strictures after stone removal.
Pathophysiology of Kidney Stones or Renal Calculus
When urine becomes concentrated, it causes a chemical reaction and when specific materials join together resulting in an object which is quite large and cannot pass through urine, it results in formation of kidney stones. Minerals like calcium oxalate and phosphate, ammonium phosphates, uric acid, calcium carbonate etc. get crystallized resulting in a hard deposit which is called renal/kidney stone. Generally, these crystals get eliminated from body through urine but in some instances they get stuck to lining of kidney or get deposited in regions where urine flow is unable to carry it. These then accumulate and become a stone. The stones can be of a size of a grain of sand to as large as golf ball. Majority of stones are formed in kidney but some may traverse to other parts of urinary system such as ureter or bladder and keep on growing in size. The common form of kidney stone is calcium stone, uric acid stone. Calcium stones are formed by build up of calcium along with oxalate, phosphate, and/or carbonate. Calcium stones accounts for more than 85% of the stones combined. Men are more prone to develop kidney stones. A build up of uric acid results in uric acid stone. They account for around 10% of the stones.
Classification and Types of Kidney Stones or Renal Calculus
Kidney stones are solid pieces of material which forms in the kidney from the substances present in urine. Normally, urine contains chemicals that prevent or inhibit the crystals from forming; however, these inhibitors sometimes do not work for everyone.
The Common Forms Of Stones Are :
- Calcium Oxalate stone.
- Calcium Phosphate Stone.
- Uric Acid Stone.
- Struvite Stone.
- Cystine Stone.
- Crixivan (Indinavir) Stone.
- Ammonium Uric Acid.
Etiology And Risk Factors of Kidney Stones or Renal Calculus
- Kidney stones are formed as a result of decrease in urine volume and presence of excessive stone forming substance in urine. The most common form of kidney stone has calcium along with oxalate and/or phosphate. Majority of kidney stones are formed of calcium.
- Dehydration increases risk for kidney stones. People residing in hot or dry regions are more prone to get dehydrated resulting in forming of stones.
- Any obstruction to the flow of urine also results in stone formation.
- Urinary tract infections can also cause formation of kidney stones. These stones are called infection stones.
- Metabolic disorders such as inherited disorder of metabolism tend to change composition of urine and increases likelihood of formation of stones.
Some Medical Conditions Also Increase The Risk Of Developing Kidney Stones or Renal Calculus:
- Gout causes chronically increased uric acid in blood and urine and results in uric acid stone formation.
- Presence of high amounts of calcium in urine is an inherited condition causing stones in more 50% of cases.
- Hyperparathyroidism, cystinuria, etc. increases the risk of stone formation.
- Medical conditions like diabetes and high blood pressure also increases risk of kidney stones.
- People who have inflammatory bowel disease are at increased risk of developing stones.
- People who have undergone intestinal surgeries are also at increased risk for stones.
- Medications like certain diuretics, antacids which have calcium in them also increase risk of stones.
- Dietary factors such as a high intake of animal proteins, excessive salt intake, excessive sugar, and foods high in oxalate like spinach also increase risk for kidney stones.
Signs and Symptoms of Kidney Stones or Renal Calculus
Kidney stones may cause severe pain whereas in some instances do not produce symptoms at all. If the stone is small in size and does not obstruct urine flow, it usually causes no pain. However, if it increases in size and passes into the ureter causing obstruction, it can result in acute and crippling pain. As the stones migrate from the kidney into the ureter towards the bladder, it causes mild to severe pain in the back. This pain moves with the stone around to the side of the abdomen as well as groin. Some patients may also have blood in their urine (hematuria). Sometimes the blood is not visible to the naked eye and is visible under a microscope. After the stone has passed in urine, it leads to a drastic reduction in the pain. Sometimes patients may also experience dull back or flank pain though it is not that common. Some patients who have large stones "sand" with discomfort, i.e. they will pass gritty material in their urine usually with blood.
In some cases kidney stones may not produce symptoms at all. These are known as "silent" stones. Mostly, patients with kidney stones have sudden onset of acute cramping pain in low back or the sides, groins, or in the abdominal area not relieved by position changes. This pain is generally waxing and waning and is called renal colic. This pain can be acute or severe to a degree that it is accompanied by nausea as well as vomiting. Patients describe this pain as worst pain they have ever experienced. Kidney stones also cause hematuria. If there is urinary tract infection with stones, then there may be fever with chills along with pain. Other symptoms like problems with urination, urinary urgency, testicular pain etc. may also be present as a result of kidney stones.
Treatment of Kidney Stones or Renal Calculus
- Majority of the kidney stones eventually pass through urinary tract by themselves within 48 hours with liberal fluid intake.
- Home care includes consuming lots of fluids, as most stones pass with increased intake of fluids.
- Ibuprofen can also used as an antiinflammatory medication.
- When over-the-counter pain control medications do not work, then Toradol, which is an injectable antiinflammatory, and narcotics are used for pain control.
- Intravenous pain medication can be given if nausea and vomiting are present.
- Factors which influence ability to pass stones are: The size of person, previous passage of stone, enlarged prostate, pregnancy and size of stone. Stones larger than 10 mm generally do not pass without treatments.
- Medications which are used to help frequency of stone passage are: medications like nifedipine and Flomax.
- If the kidney stones do not pass by themselves, then a procedure named lithotripsy is carried out. This procedure is done by using shock wave to shatter a large stone into smaller fractions to allow them to pass easily through urinary system.
- If these treatment methodologies are ineffective in stone removal, then surgical procedures are done by making a small incision in skin or via an instrument called ureteroscope which is passed through urethra and bladder up into ureter.
- Preventative measures which can be taken to avoid formation of kidney stones are: Drinking more water, dietary changes. People prone to formation of kidney stones based on calcium oxalate need to limit their consumption of foods high in oxalates like spinach, beets, wheat germ etc.
Investigations for Kidney Stones or Renal Calculus
- Medical history and physical examination.
- A helical CT scan without contrast material is a common test to detect stones or obstruction within the urinary tract.
- Intravenous Pyelogram (IVP) can also detect urinary tract stones, but this test carries a high risk of complications, takes longer, and involves higher radiation exposure than thenon-contrasted helical CT scan.
- Ultrasound examination can be done in pregnant women or those people who should avoid radiation exposure.
- CT scan.
- Tests such as urine studies to look for blood.
- CT urography.