A 42-year-old woman undergoes imaging for flank pain and is found to have a ureteric stone. Non-contrast CT shows the stone is located at the level of the pelvic brim, just above the pelvic inlet. At which of the following sites is a ureteric stone most commonly impacted?

Explanation

## Most Common Site of Ureteric Stone Impaction **Key Point:** The **ureterovesical junction (UVJ)** is the most common site of ureteric stone impaction, accounting for approximately 60–70% of all ureteric calculi. It is the narrowest segment of the entire ureter. ### Three Physiological Narrowings of the Ureter | Site | Location | Frequency of Impaction | Anatomical Reason | |---|---|---|---| | Ureteropelvic junction (UPJ) | Junction of ureter and renal pelvis | ~20% | Transition zone; relatively narrow | | Crossing of iliac vessels / Pelvic brim | Where ureter crosses common iliac vessels at pelvic inlet | ~20% | Change in direction; vascular compression | | **Ureterovesical junction (UVJ)** | **Intramural portion of ureter entering bladder** | **~60–70%** | **Narrowest part of ureter; oblique intramural course** | ### Why UVJ is the Most Common Site **High-Yield:** The UVJ is the **single most common site** of ureteric stone impaction because: 1. **Narrowest lumen** — the intramural ureter (1–5 mm) is the narrowest segment of the entire urinary tract 2. **Oblique course** — the ureter traverses the bladder wall at an oblique angle, further reducing the effective lumen 3. **Functional valve mechanism** — the ureterovesical valve prevents vesicoureteral reflux but also creates a physiological bottleneck for descending stones ### Clinical Pearl Per Campbell-Walsh-Wein Urology (12th ed.) and Bailey & Love's Short Practice of Surgery (27th ed.), the UVJ is cited as the most frequent site of stone impaction. Stones here classically cause pain radiating to the ipsilateral testis/labium majus (L1 dermatome) and may produce urinary urgency/frequency due to bladder irritation. ### Regarding the Other Options - **Option A (Crossing of iliac vessels):** This is anatomically the same region as the pelvic brim/pelvic inlet — where the ureter crosses the common iliac vessels. It accounts for ~20% of impactions and is a genuine narrowing, but is **not** the most common site. - **Option B (Ureteropelvic junction):** Accounts for ~20% of impactions; the second most common site overall. - **Option D (Pelvic brim/pelvic inlet):** The pelvic brim and the crossing of iliac vessels refer to the same anatomical region. This is a common site (~20%) but not the most common. Some older Indian surgical texts have listed it as most common, which is a source of confusion; contemporary references consistently rank the UVJ as most common. ### Imaging Findings at UVJ - **Non-contrast CT (NCCT):** Stone at the ureterovesical junction with proximal hydroureteronephrosis; "rim sign" (periureteral edema) may be present - **Ultrasound:** Dilated ureter and renal pelvis; stone may be visible just above bladder entry - **Plain radiograph:** Radiopaque stone overlying the bony pelvis near the bladder base ### Management Implications - **Expectant management:** Stones <5 mm at UVJ have ~70–80% spontaneous passage rate; alpha-blockers (tamsulosin) facilitate passage - **Intervention:** Ureteroscopy with laser lithotripsy for stones >10 mm or those failing conservative management **Reference:** Campbell-Walsh-Wein Urology, 12th edition; Bailey & Love's Short Practice of Surgery, 27th edition.