Ureteric Constrictions

Ureteric constrictions are anatomical narrowings along the course of the ureter where the lumen is naturally smaller. These sites are clinically important because they are common locations for obstruction by kidney stones (urolithiasis), narrowing due to fibrosis, or injury during surgery. Most individuals have three classical sites of constriction along the ureter.

Classical Constriction Sites

Constriction Site Location Clinical Note 1. Ureteropelvic junction (UPJ) Where the renal pelvis transitions into the ureter Most proximal narrowing; common site for congenital obstruction 2. Pelvic brim Where the ureter crosses the common/external iliac artery Ureter is compressed between the artery and pelvic wall 3. Vesicoureteric junction (VUJ) Where the ureter enters the posterolateral aspect of the urinary bladder Most common site of stone impaction overall

Functional Significance

• Transit regulation: These narrowings may slow urine flow, which can help modulate pressure transmission

• Reflux prevention: At the vesicoureteric junction, a functional flap valve prevents backflow of urine during bladder contraction

Clinical Relevance

• Kidney stones: Stones ≥5 mm often become lodged at constriction points, especially the VUJ

• Ureteric colic: Pain is most severe when stones are stuck at a constriction and cause proximal dilation

• Hydronephrosis: Obstruction at any of these points can lead to urine back-up and renal pelvis dilation

• Surgical planning: Awareness of constrictions helps avoid damage during stenting, ureteroscopy, or open surgery

Additional (Variable) Constriction Sites

Some individuals may exhibit additional mild constrictions, particularly:

• At the crossing of the gonadal vessels in the abdomen

• Near the iliac bifurcation, especially in cases of vessel tortuosity

Despite variability, the three classic sites remain the most clinically significant and are key to interpreting ureteric imaging and managing urinary tract obstruction.