Which structure does the renal calculus commonly obstruct as it passes through the ureter?

• A. Ureteropelvic junction
• B. Ureterovesical junction
• C. At the pelvic brim
• D. The infundibulopelvic ligament

Answer: (C)

The renal calculus, or kidney stone, commonly obstructs certain anatomical landmarks as it moves through the ureter. Among these potential sites, the pelvic brim is notable due to its critical position in the urinary tract.

As kidney stones descend from the renal pelvis through the ureter, they may encounter various constricting points. The pelvic brim represents one of these natural constrictions where the ureter crosses the pelvic inlet at the level of the sacral vertebrae. This region can act as a significant barrier due to the narrowing of the ureter, often leading to an obstruction if a calculus is present.

In addition, the ureteropelvic junction and ureterovesical junction are also sites that typically can experience obstruction from urinary calculi. However, the pelvic brim is the specific area that this question highlights, regarding the anatomical location through which a stone traditionally obstructs as it descends into the ureter.

Thus, the presence of a stone at the pelvic brim is a common occurrence and aligns with clinical observations regarding the passage of renal calculi through the urinary tract.