1. Development History of Ureteral Stents
In the first half of the 18th century, Lorenz Heister, the pioneer of stent technology, developed a type of catheter with a naturally curved bottom for the urethra, and the development of ureteral stents can be said to have relied on this invention.
Over time, by the end of the 19th century, J. Eynard produced catheters that came in three types but lacked X-ray opacity until Roentgen's discovery of X-rays, leading to the necessity for catheters visible under X-rays.
Ureteral stents have continued to evolve over time, made from various materials such as synthetic plastic, coated fabric, etc. Until 1967, Zimskind described ureteral stents for the first time, and since then, they have become an indispensable tool for urologists, paralleling the demand for less invasive urological treatments.
2. Characteristics of Ureteral Stents:
- Excellent radiopacity.
- Easy to operate.
- Durable after placement.
- Biocompatible.
- Chemically stable in urine.
- Resistant to encrustation and infection.
- Provides good and long-lasting flow.
- Does not cause irritating symptoms.
- Affordable.
3. Indications for Ureteral Stent Placement
- In urinary stone diseases.
- Postoperative treatments: Retrograde intrarenal surgery, extracorporeal shock wave lithotripsy, percutaneous nephrolithotomy, etc.
- Secondary renal insufficiency due to obstruction.
- Trauma, benign ureteral strictures, ureteric fistulas, etc.
4. Symptoms after Ureteral Stent Placement
Although modern ureteral stents have greatly improved in quality and design, there may still be some common symptoms after placement, such as:
- Bladder irritation symptoms, flank pain, discomfort in the lower abdomen, hematuria without urinary tract infection.
- Urgency, frequency, or difficulty urinating.
However, these symptoms have been significantly reduced with the use of advanced stents and under the close monitoring of urologists, and are usually effectively managed.
- Duration of stent placement: There is no specific duration for stent retention; however, depending on the patient's condition and clinical status, the urologist will consider whether to retain or remove the stent. Stent retention can last up to one year for types of stents with reduced encrustation and infection. Typically, ureteral stents are retained for approximately 1-3 months.
5. Physiological Changes after Ureteral Stent Placement
When a double-J stent is placed in the ureter, bladder pressure can transmit retrogradely to the kidney, increasing the acute pressure within the kidney. This pressure gradually decreases and returns to normal after about 3 weeks and is directly related to the diameter and flow characteristics of the ureteral stent.
Urinary flow occurs both inside and outside the ureteral stent, except in cases of ureteral strictures, where urine can only flow inside the stent. Therefore, as the diameter of the double-J stent increases, the flow rate also increases. Additionally, urinary flow depends on various factors such as kidney pressure, stent diameter and length, bladder pressure, and urine density.
Moreover, the side holes of the double-J stent play a significant role. Stents without side holes are associated with a 40-50% reduction in flow diversion compared to those with side holes. Double-J stents cause passive dilation of the ureter due to cell toxicity or infection. Ureteral peristalsis is often reduced but returns to normal within a short period. Additionally, double-J stents increase mucus secretion and induce histological changes in the ureteral wall.