How to Approach Uroliths from the Kidney to the Urethra

 Minimally invasive techniques to treat urolithiasis require specialized equipment to fragment the stones, such as the Holmium:YAG laser.  The Holmium:YAG laser has not been successful in fragmenting all uroliths in horses, and smaller stones may be easier to fragment with this laser.  Other means for lithotripsy include ballistic and electrohydraulic lithotripters, but these cannot be used with flexible endoscopes. The prevalence of urolithiasis in equines is thought to be low (0.04-0.7% of equines, depending on the sample population), and uroliths have been found most commonly in the bladder, but can occur anywhere within the urinary tract. Geldings and stallions are more commonly affected than mares, likely due to the smaller diameter of the urethra in males. Most uroliths in horses are made of calcium carbonate in calcite crystal form, with variable amounts of other minerals. 1 A clinical workup for horses with urolithiasis should include a thorough ultrasound exam of the whole urinary tract, bloodwork to determine kidney function, as well as cystoscopy, in addition to a regular physical exam. After determination of location and size of the urolith(s), the feasibility of a minimally invasive approach should be assessed. Whether or not such approach is chosen will depend on availability of equipment, experience and comfort of the surgeon with the equipment, location and size of the urolith(s) and financial commitment of the owner. Two challenges have to be overcome for the minimally invasive removal of uroliths: most stones will have to be fragmented effectively to be removed through natural orifices or small incisions, and removal of the fragments has to be reliable and complete. Minimally invasive devices to fragment stones include laser lithotripters, ballistic and electrohydraulic lithotripters, and possibly extracorporeal shockwave units and their use is described below with respect to lithotripsy of cystic calculi. Laser lithotripsy in horses has been reported using the Pulsed Dye Laser (wavelength 504 nm)or the Holmium:YAG Laser (wavelength 2,100 nm) and it provides the advantage of fragmentation under visual guidance with a flexible endoscope, as both wavelengths can be transmitted via a flexible fiber. The Pulsed Dye Laser is very effective at fragmenting large uroliths, but because of its costly maintenance and the greater effectiveness of the Holmium:YAG Laser in human endourology, it is no longer available, to this author’s knowledge. The Holmium:YAG Laser has received mixed reviews with respect to its effectiveness at fragmentation of larger stones in horses. In 7 of the 15 reported cases, laser lithotripsy either did not affect the stone at all (3 of 7cases), or resulted only in creation of a crater or groove (maximum 2cm deep) and laser lithotripsy was abandoned at that point (4 of 7cases). In the remaining 8 of the 15 reported cases, fragmentation of the uroliths into fragments of maximum 1 cm diameter was successful. Possibly, smaller uroliths are more likely to be fragmented successfully than large uroliths, although urocystoliths as large as 12 cm in diameter have been fragmented successfully. Laser lithotripsy of cystic calculi is performed in standing, sedated horses via the biopsy channel of a flexible endoscope either through a perineal urethrotomy or through the urethra, even in male horses. Continuous lavage with saline solution facilitates visualization and prevents overheating of the bladder, although periodic lavage with the endoscope removed is oftentimes needed to regain adequate visibility of the