Kidney Stone Institute

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Kidney Stone Institute

Kidney Stone Terms

The purpose of the urinary tract is to filter waste products from the blood and excrete these substances and excess water in the form of urine. Find out about:

Kidney regions

kidney regionsBladder - the storage area for urine between episodes of urination.

Calyx - beginning of the urine collecting system. A kidney typically has 6-10 calyces. Stones in the kidney are typically found within a calyx. During stone surgery it is essential to be able to inspect all calyces for stones and stone fragments.

Collecting System - term used to refer to the entire area from bladder to calyces.

Cortex - outer solid portion of kidney where blood is filtered.

Distal ureter - the final portion of the ureter. The portion of the ureter between the bony pelvis and the bladder. The narrowest portion of the ureter is found as the ureter enters the bladder. Stones in this location will often pass spontaneously. Until they do they usually irritate the bladder and produce symptoms similar to bladder infections.

Infundibulum - the infundibulum is the passage from the calyx to the renal pelvis. A single infundibulum may accept urine from several calyces. A kidney will usually have three to seven infundibulae.

Lower pole - the bottom part of the collecting system. Stones in this location are generally the most difficult to treat. Stone fragments tend to persist in this location and act as seeds of recurrent stones.

Medulla - inner solid portion of kidney where urine is formed and concentrated.

Mid pole - middle portion of the collecting system usually composed of infundibulae which often drain a single calyx.

Middle Ureter - the portion of the ureter which overlies the bony pelvis. The ureter narrows as it crosses over the large blood vessels supplying the legs. Stones often become lodged in this position. Because these stones overly the bone, they are not easily seen by regular x-rays and are poor candidates for ESWL therapy.

Papilla - extreme end of pyramid where urine leaves the kidney. This is the area where kidney stones are thought to begin.

Pelvis - the renal pelvis is the central point to which all infundibulae drain. In the renal pelvis stones may grow to large size.

Proximal ureter - the portion of the ureter between the kidney and the bony pelvis. Stones often become lodged in this area. In the past, stones in this position were difficult to treat safely. Now this area is readily accessed with a flexible ureteroscope.

Pyramid - area of medulla where urine is excreted into drainage system.

Upper pole - the top portion of the collecting system usually drained by 1-2 infundibula and 3-5 calyces.

Ureteropelvic Junction - the region where the renal pelvis joins the ureter. This is the first narrowing into which stones may get stuck as they pass out of the renal pelvis. Stones obstructing in this area often fall back into the kidney and are associated with episodic symptoms.

Ureter - the ureter is the long narrow muscular tube which allows urine to drain from the kidney to the bladder.

Urethra - the connection between the bladder and the outside world.


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Kidney stone terminology

Crystal - microscopic organized aggregation of salts which can grow into a stone.

Fragment - pieces of stone after breaking a stone during treatment. Urologists have only been able to confidently detect fragments since CT scans gained widespread use and we are unsure of their significance. In general stone fragments less than 2 mm are unlikely to cause significant problems. Fragments between 2 and 4 mm may potentially cause problems, but have a reasonable chance of passing on their own and treatment of asymptomatic stones is generally not recommended. Fragments greater than 4 mm are likely to cause problems if they leave the kidney and are generally a sign of treatment failure if they persist after an attempt to clear a stone.

Randall’s Plaques - small calcium deposits on the tips of the renal papilla. These are increasingly thought to play an important risk factor for future stone formation.

Renal colic - term used to describe the common severe symptoms associated with a kidney stone obstructing the ureter. Common complaints include unpredictable onset of severe pain, usually beginning in the back and radiating to the groin. Nausea and vomiting often accompany this severe pain. Patients suffering renal colic are easy to identify in the emergency room as they are often found in agony draped over the admitting nurse’s desk.

Staghorn Stone - a unusual type of stone usually associated with chronic urinary tract infection. These large complex stones can fill an entire kidney and if untreated can destroy a kidney and may be a threat to life. These stones are usually treated by percutaneous nephrolithotomy.

Stone - crystal which has grown large enough too be seen. Stones less than a millimeter can be discovered with a CT scan. The largest stones can be as big as your fist.

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Kidney stone treatment terminology

Cystoscope - specialized endoscope for examination and treatment of urethra and bladder. Usually 6-8 mm in diameter.

Endoscopes - a wide variety of specialized telescope like instruments are used in stone treatment. They are available in different sizes and in rigid and flexible forms. Each endoscope has specific advantages and limitations and availability of proper instrumentation for a particular situation is essential.

Extracorporeal Shock Wave Lithotripsy (ESWL) - radiologically guided destruction of stones by ultrasonic shock waves.

Lithotripsy - the process of breaking stones.

Nephroscope - specialized endoscope for examination and treatment of kidney disease. Usually 8-9 mm in diameter.

Nephrostomy Tube - plastic tube used to drain the kidney through a hole in the back into a urine collection bag. Tubes vary in size from 2-7 mm.

Percutaneous Nephrolithotomy (PCNL) - clearance of stones working through a tunnel created through the back into the kidney. Stones are destroyed or removed intact.

Stent - small (about 2 mm diameter) plastic tube used to temporarily drain the kidney when the ureter is obstructed or non-functional.

Ureteral Access Sheath - a 4 mm diameter tube used to provide rapid access to the ureter and kidney. Very effective for ureteroscopic clearance of kidney stones.

Ureteroscope - specialized endoscope for examination and treatment of ureteral disease. Usually less than 3 mm in diameter

Ureteroscopy - treatment of stones with small scopes passed up the urinary tract through the urethra. Stones are directly visualized and destroyed with a laser or extracted intact.

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Radiology tests

CT scan - computed tomography (CT) is the most effective way to look for kidney stones. It uses radiation and computers to generate a cross-sectional view of the abdomen and pelvis. Usually performed without contrast for stone disease. If other non-stone issues are being addressed, administration of oral and intravenous contrast media may be required

Flouroscopy - flouroscopy is used during stone surgery to provide live images.

Intravenous Pyelogram - intravenous pyelography was the traditional test used to examine the urinary tract in detail. It uses radiation and intravenous injection of contrast media to demonstrate the collecting system. As this test has largely been replaced by the more accurate CT, the IVP is rarely requested and limited to addressing specific questions which it can uniquely answer.

Magnetic Resonance Imaging - MRI generates images by the highly sensitive detection of vibration of water molecules in response to a pulse of high power magnetism. Unfortunately, because kidney stones contain minimal water they are seen only as “black holes” on MRI images.

Plain x-ray - plain x-rays of the kidney, ureter and bladder (KUB) are the traditional method of looking for kidney stones. One or two x-rays pictures are taken using radiation. Unfortunately this test tends to miss many stones.

Ultrasound - imaging using ultrasonic energy to look into the body. Unfortunately it is a poorly reliable test for kidney stones but is often used during pregnancy when radiation based imaging is avoided.

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A doctor's referral is not required to make an appointment.

1-888-326-3830 (toll-free)


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Outside of these hours, you can call us and speak with a registered nurse who will review your symptoms and make recommendations to help you get appropriate care.