What is the STING Procedure and What Does an Ectopic Kidney Mean?
STING Procedure
The STING procedure (Subureteral Transurethral INjection) is a minimally invasive endoscopic technique that involves injecting a bulking agent (0.2-0.8 ml) beneath the intravesical portion of the ureter to create a valve mechanism that prevents backward flow of urine from the bladder into the kidney (vesicoureteral reflux). 1
How It Works
- The procedure uses cystoscopy to inject bulking material (historically Teflon/polytetrafluoroethylene, now more commonly dextranomer-hyaluronic acid copolymer [Deflux®] or polyacrylate-polyalcohol copolymer [Vantris]) into the submucosal space at the ureterovesical junction
- This creates a "mound" that lengthens and supports the ureteral tunnel, preventing reflux 2
- The injection can be performed using different techniques, with STING and HIT (hydrodistention implantation technique) being the two main approaches 2
Success Rates and Considerations
According to the most recent European guidelines, endoscopic injection has variable success rates depending on reflux severity 3:
- Grade I-II reflux: 78.5% success with one treatment
- Grade III: 72% success
- Grade IV: 63% success
- Grade V: 51% success
- If the first injection fails, a second attempt has 68% success, and a third has 34% success
- Overall aggregate success with one or more injections reaches 85% 3
Important Caveats
- Success rates are significantly lower in duplicate collecting systems (50% vs 73% for single systems) and neuropathic bladders (62% vs 74% for normal bladders) 3
- The procedure carries a risk of late ureteric obstruction, particularly with older materials like Teflon, which can cause giant-cell foreign-body granulomas requiring ureteric reimplantation years later 4
- Modern bulking agents (Deflux® and Vantris) have different properties: Deflux is absorbable, easier to inject with lower obstruction risk but may lose efficacy over time; Vantris is non-absorbable, more difficult to inject with higher obstruction risk but potentially more durable 2
Ectopic Kidney
An ectopic kidney is a congenital anomaly where the kidney fails to ascend to its normal lumbar position during fetal development and remains in an abnormal location, most commonly in the pelvis. 5
Key Characteristics
- Occurs in approximately 1 in 900 to 1 in 3,000-7,000 individuals 5, 6
- Results from arrested migration during embryogenesis when the kidney normally ascends from the pelvis to the lumbar region
- Can be simple ectopia (abnormal location on the same side) or crossed ectopia (ureter crosses the midline) 6
Clinical Significance
While often asymptomatic, ectopic kidneys are more susceptible to complications due to their abnormal positioning 5:
- Ureteropelvic junction obstruction (UPJO) - the most common complication
- Recurrent urinary tract infections
- Stone formation
- Vesicoureteral reflux
- Abnormal vascular supply (often from iliac arteries rather than the aorta) 6
- May present as a pelvic mass in adults 7
Diagnostic Approach
- Ultrasound is the first-line imaging modality
- Three-dimensional CT urography provides detailed anatomical information about the kidney's position, vascular supply, and any associated obstruction 6
- DMSA scan or DTPA renogram assesses differential kidney function 7
Management Considerations
- Treatment depends on whether the ectopic kidney is functioning and whether complications are present
- For non-functioning ectopic kidneys with severe hydronephrosis, nephrectomy prevents long-term complications 7
- For functioning kidneys with obstruction, minimally invasive approaches like laparoscopic pyeloplasty can be performed, though the abnormal anatomy and vascular supply require careful surgical planning 6
- When treating vesicoureteral reflux in a solitary ectopic kidney, modified endoscopic techniques with guidewire assistance can be used to ensure precise injection placement and avoid complications 8