Ureteroscopes: overview and technical specifications
Ureteroscopy has become the mainstay of treatment for ureteral stones and intrarenal stones smaller than 1.5 cm and refractory to ESWL. In the past several years ureteroscopes have become smaller and more technologically advanced with better optics to facilitate ureteroscopic management of nephrolithasis. This article reviews the technical specifications of flexible and semi-rigid ureteroscopes.
Flexible ureteroscopes (Figure 1) have one working channel, a deflecting tip, and a fiberoptic viewing system (Figure 2). An “intuitive” scope has a deflection direction that coincides with the direction of the deflection control, so moving the thumb control down moves the tip of the scope down. The angle deflection can range from 1800-3100, allowing for visualization of the entire upper urinary tract including each renal calyx. The working channel on flexible ureteroscopes is typically 3.6 French (Fr), allowing for irrigation and up to a 3 Fr working device for laser fibers, baskets, grasping forceps, etc. If multiple passes into the ureter are expected, then a ureteral access sheath can be used. This facilitates repeat ureteroscopy by obviating the need to run the scope up the ureter over a wire (or enter the ureter freehand), thus saving time in the operating room. Access sheaths range from 10 fr-16 Fr and are listed by inner/outer diameter such that an 11/13 access sheath has a inner diameter of 11 Fr and outer diameter of 13 Fr. Typical lengths are 20, 28, 35, and 55 cm. Choice of length is dictated by sex (shorter in female) and location of access point (longer for more proximal). For example, a 35 cm sheath is good for proximal access in a female and mid-ureteral access in a male.
Technical specs on the most commonly employed flexible ureteroscopes are as follows:
- ACMI DUR-8 Elite – Distal diameter 8.7 Fr, working channel 3.6 Fr, length 64 cm, deflection 310° up and 170° down
- Storz Flex-X - Distal diameter 7.5 Fr, working channel 3.6 Fr, length 67 cm, deflection 270° up and down
- Olympus URF-P5 - Distal diameter 5.3 Fr, working channel 3.6 Fr, length 70 cm, deflection 180° up and 275°
|Figure 1: Flexiable Urteroscope|
|Figure 2: View from Flexible Urteroscope|
Most semi-rigid ureteroscopes (Figure 3) have dual working channels--one for irrigation and one for a wire, laser fiber, basket, etc. These chambers range from 2.5 Fr to 3.6 Fr. Those with only 1 working channel have variable sizes from 4-6 Fr. They also vary in length from 33-42.5 cm, some models also have a slight angle to them to facilitate passage in the ureter. Semi-rigid ureteroscopy is preferable for distal ureteral stones. Once above the iliac vessels rigid semi-rigid ureteroscopy can become difficult and dangerous as the ureter may not be as flexible above this point and the rigid scopes don’t bend very well, although proximal access may be feasible in female patients. For stones above the point of safe passage, flexible ureteroscopy is best.
Technical specs on the most commonly employed semi-rigid ureteroscopes are as follows:
- Gyrus ACMI MICRO-6 – 41 cm long, 6.9 Fr diameter, working channel #1=3.4 Fr and #2=2.3 Fr.
- Gyrus ACMI MICRO-7 -33 cm or 42 cm long, 7.7 Fr diameter, working channel #1=5.4 Fr.
- Stryker RU - 33cm long, 6.9 Fr diameter, working channel #1=3.4 Fr and #2=2.5 Fr.
- Storz 27410SK – 34 to 43 cm long, 7.5 diameter, working channel #1=3.6 Fr and #2=2.5 Fr.
|Figure 3: Semi-Rigid Urteroscope|
|Andrew Harris, MD
Chief Resident, University of Pennsylvania