This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
The pain in the lateral thigh and pubic regions continues to be intense and unremitting. The patient is admitted to the hospital for observation and possible surgical intervention. Given this paicular pattern of renal colic and the anatomy of the renal system, it is suspected that a stone has stopped moving and is lodged. 
Select and explain. 
A. At the junction of the renal pelvis and ureter, B. Midureter as it passes beneath the gonadal vessels, C. At the pelvic brim, D. In the intramural poion of the ureter where it penetrates the bladder
C: At the pelvic brim
Answer: C: At the pelvic brim 
Explanation: The ureters narrow at the renal pelvis, at the pelvic brim, where they cross the iliac vessels and enter the deep pelvis, and at the urinary bladder. Thus, the probability of a nephrolith lodging in the ureter at the pelvic brim is high and is confirmed by the pattern of referred pain.