Most people do not realize that about one third of the kidney is hollow on the inside. This portion is called the collecting system. Kidney stones rest in the collecting system until they attempt to pass down through the ureter toward the bladder. The ureter is the tube that connects the kidney to the bladder.
Stones that are simply resting within the hollow part of the kidney usually do not cause pain. When stones try to pass down the ureter toward the bladder, they have the potential to cause pain. Pain that is the result of a kidney stone occurs when the stone completely or partially blocks the flow of urine from kidney to bladder. This can happen where the kidney meets the ureter or at any point along the course of the ureter. The pressure increases upstream from the point of obstruction and causes severe pain. Think of it like a running garden hose - if someone kinks the hose, all the pressure builds up upstream from the kink. If this happens in the ureter and kidney, then it results in the severe pain and spasms known as "renal colic."
To see a diagram of the Anatomy of the Urinary System.
Expectant Management (trying to pass the stone)
In general, the larger the stone, the less likely it will be to pass. That being said, many patients are able to successfully pass quite large stones, particularly if they have previously passed stones.
Surgical Options - Stones 2 cm or smaller
Surgical Options – Stones larger than 2 cm
Stones this large are best treated with a procedure called a Percutaneous Nephrolithotomy (PCNL). This is performed by using larger telescopes and instruments placed directly through the back and into the kidney. The stone is then broken up and the pieces are sucked out. A radiologist will place a guidewire through the back immediately prior to surgery to allow access for the larger scopes. After the procedure, the patient will have 2 catheters coming out of their back. One is usually removed the day after surgery and the larger tube is usually removed a few days later in the office. Typically a PCNL requires an overnight stay in the hospital.
See a picture of how PCNL works.