How to choose stent size and length
The choice of diameter is dictated by the nature of the obstruction. In benign strictures, the tissues are compliant, and urine can drain around the outside of the tube as the ureter dilates—a 6 F stent is sufficient. In malignant and ischemic lesions, the wall is rigid, no dilation occurs, and therefore an 8 F stent is required.
Length is determined in two ways:
- Height-based calculation (most reliable): for height up to 175 cm, a 22 cm stent is used; 175–195 cm — 24 cm; above 195 cm — 26 cm.
- Direct measurement using markers on the guidewire, but this method is often erroneous in a tortuous ureter.
Exceptions: for an urostomy, the stent should be no longer than 22 cm; for a kidney transplant, 12 cm is sufficient.
Plastic and metallic stents
Polymeric (plastic) stents are cost-effective and easy to place. However, they frequently encrust with salts, cause severe dysuria, and require regular replacement. Devices with a hydrophilic coating pass through strictures more easily but are more expensive.
Metallic stents last significantly longer, but are harder to position and prone to migration.
- Memokath is made of nitinol (a shape memory alloy). When flushed with 50°C water, it expands, fixing securely. Cold water makes it contract, allowing the stent to be easily removed even after several years.
- Uventa and Allium are self-expanding, large-caliber, long stents (20–30 F).
Important: after metal placement, the mucosa often swells. To be safe, a temporary nephrostomy for 24 hours may be required.
Insertion technique and troubleshooting
First, the stricture is dilated with a balloon or bougies. Then the stent is pushed over a stiff guidewire. Ideal position: the upper pigtail curl is in the renal pelvis, and the lower one is just beyond the ureterovesical junction (an excessively long loop in the urinary bladder increases pain).
Difficult situations:
- Tortuous ureter: navigated using a combination of a hydrophilic guidewire and a curved-tip catheter, then straightened with a stiff guidewire and a peel-away sheath.
- Formation of a false passage: the procedure is stopped immediately. Antibiotics are prescribed, a safety nephrostomy is placed, and the attempt is repeated in 3–7 days.
- Impassable stricture: the push-pull maneuver is used — the tip of the guidewire is snared in the urinary bladder and pulled out through the urethra, allowing the stent to be advanced with force.
Replacement and removal
Plastic models are replaced primarily retrogradely: in a filled bladder, the lower curl is snared, the stent is extracted outward, and a guidewire for the new tube is introduced directly through its lumen.
Monitoring stent function by ultrasound alone can be misleading (reflux itself causes upper tract dilation), so the picture is always correlated with blood biochemistry.
Briefly: answers to topical questions
What early and late complications are possible after ureteral stenting?
The following complications are possible after ureteral stenting:
- Dysuria — pronounced stent-related symptoms; an excessively long loop in the urinary bladder increases dysuria.
- Encrustation — frequently occurs with plastic stents.
- Infection.
- Hematuria.
- Occlusion — any stent eventually becomes occluded.
- Migration (dislodge) — metallic stents are prone to displacement.
- False passage — a complication that may occur during stricture cannulation.
- Erroneous placement of the stent tip in the perirenal space — a possible insertion complication requiring repositioning.
What diagnostic imaging methods are used to monitor the position and function of a ureteral stent?
A combination of various diagnostic imaging methods is used to monitor the position and function of ureteral stents, as no ideal method exists.
- Ultrasound — with Doppler sonography to assess the resistive index or ureteric jets. Conventional ultrasound may be uninformative due to reflux along the stent, so its findings are correlated with blood biochemical parameters.
- Intravenous urography — used to assess patency.
- Cystography — used in contrast or radionuclide variants.
- Renography — performed, inter alia, with the use of a diuretic.
Rule of caliber: "Benign gets 6, Malignant gets 8". In benign processes, 6 F is enough (the ureter will stretch); in malignant tumors, tissues are rigid — an 8 F lumen is needed.
Class and exam questions
What to do if the lower end of the stent is mistakenly placed in the perirenal space?
It can be retrieved retrogradely (by snaring it through the bladder) or antegradely (by performing a new renal puncture, catching the stent with a catheter and snare, and pulling it back into the system).
How to eliminate the formation of guidewire loops in the retroperitoneal space?
It is necessary to maintain access using a super-stiff guidewire and a peel-away sheath, the size of which must be 1 F larger than the stent itself.
What is the problem with stenting a ureteroileal anastomosis?
Mucous obstruction (requiring a lumen >8 F) and urine reflux due to bowel peristalsis may occur. The solution is to bring the distal end of the stent directly outward into a urostomy bag.
What else to study on this topic
- High-pressure balloon dilation of ureteral strictures
- Rendezvous technique in extra-anatomic stenting
- Percutaneous management of ureteral fistulas and urinary leaks
- Suprapubic bladder catheterization under ultrasound guidance
- Ureteral occlusion technique for severe incontinence
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