Clinics & Inpatient Care Units

Urology - Kidney Stone Centre

Kidney Anatomy

The kidneys are two bean-shaped organs found under the ribs on either side of the upper abdomen. They filter toxins and excess water from the blood to produce urine, produce important hormones, regulate blood pressure and regulate the level of blood electrolytes.

Urine produced by the kidneys drains through thousands of tiny tubules into the renal pelvis. It then drains down to the bladder through a tube called the ureter.


Lower Urinary Tract

The ureters drain urine into the bladder, which is then emptied via the urinary passage (the urethra). Pain usually disappears once kidney stones pass into the bladder. It is much easier, and usually painless, for stones to pass out through the urethra, because the urethra is about twice the diameter of the ureter.

Stones can form in the bladder as well, but bladder stones are treated differently than kidney stones. Bladder stones are much more common in men and are usually caused by infections or bladder blockage from the enlargement of the prostate.

Telescopes can be passed up the urinary passage (the urethra) and into bladder. A telescope for looking at the inside of the bladder is called a cystoscope, and can be used to perform a special X-ray test called a retrograde pyelogram (IVP or CT or U/S) or to insert a small tube called a stent to unblock a kidney. An even smaller telescope, called a ureteroscope, can be inserted into the ureter and passed up to the kidney to break up and remove many types of stones.


Anatomic Anomalies Promoting Stones

Horseshoe kidney – this occurs when the kidneys become fused together in the middle. They are usually found lower in the abdomen than is usual and often have a narrow ureteropelvic junction (UPJ). Kidney stones may develop and result in blockage at the UPJ.

Solitary kidney – sometimes only one kidney forms instead of two. This only becomes a problem if that single kidney becomes blocked with a kidney stone.

Pelvic kidney – normally during fetal growth the kidneys rise from the pelvis into the upper abdomen. Sometimes this does not happen so that one kidney is in its normal position, while the other kidney remains in the pelvis.

Medullary sponge kidney – some people have kidneys that are more prone to form kidney stones because the tiny tubules that drain into the renal pelvis are larger than normal, resulting in slower drainage and crystal formation.

Crossed, fused renal ectopia – sometimes one of the kidneys can cross to the wrong side during fetal development and fuse with the other kidney. This abnormality of development seldom causes any problems.

Kidney stones can also form if a kidney is partially blocked, as urine becomes stagnant in the kidney resulting in crystal and stone formation. Blockage of the kidney causes it to swell – a process called hydronephrosis that can be diagnosed by ultrasound or X-rays.

There are many other reasons for kidney stones to form, and many are listed on the risk factors page.