A ureterolith is a kidney stone that has moved from its formation site into the ureter, the tube connecting the kidney to the bladder. Once lodged, it can cause obstruction and discomfort.
Anatomy of the Ureter
The ureters are muscular, narrow tubes that transport urine from the kidneys to the urinary bladder. Each ureter measures approximately 20 to 30 centimeters (8 to 12 inches) in length and has a diameter of 3 to 4 millimeters. Urine moves through these tubes not by gravity alone, but through wave-like muscular contractions called peristalsis, which propel the urine downward.
Originating from the renal pelvis in each kidney, the ureters descend through the abdomen and into the pelvic cavity. They are situated behind the peritoneum. The ureters follow an “S” shaped curve, passing over various structures before finally entering the bladder. This pathway is important for understanding where stones might encounter resistance.
Common Obstruction Sites
Ureteroliths are most commonly located at specific points along the ureter where natural narrowings occur. The first common site is the ureteropelvic junction (UPJ), the area where the renal pelvis, the funnel-shaped part of the kidney that collects urine, transitions into the ureter. This is the most superior constriction point.
A second frequent location for obstruction is where the ureter crosses over the iliac blood vessels as it enters the pelvis. This crossing represents a natural bend and narrowing in the ureter’s path, making it susceptible to stone impaction.
The third and most common site for a ureterolith to become lodged is the ureterovesical junction (UVJ). This is the point where the ureter enters the bladder wall. The ureter passes obliquely through the bladder wall, creating a narrow segment that acts as a one-way valve to prevent urine backflow into the kidneys. This intramural portion is the narrowest part of the entire ureter.
Impact of Location
The specific location of a ureterolith significantly influences the type and intensity of symptoms experienced. A stone lodged in the upper ureter, near the kidney, often causes pain in the flank or lower back. This pain may be dull or sharp and can be felt in the side or back without radiating to other areas.
As the ureterolith moves lower in the ureter, the pain shifts and may radiate. Stones in the mid-ureter can cause pain that moves towards the front of the abdomen or lower down into the groin. When a stone reaches the distal ureter, close to the bladder, it can lead to symptoms that mimic bladder issues, such as increased urinary frequency, urgency, or discomfort during urination. The location of the stone also guides diagnostic imaging choices and is important for determining the management approach.