Interventional Strategies for Urinary Disease

Chapter 195


Interventional Strategies for Urinary Disease




Interventional endoscopy (IE) involves the use of endoscopic visualization with other contemporary imaging, such as fluoroscopy, ultrasonography, or both, to perform minimally invasive diagnostic and therapeutic procedures. Interventional radiology (IR) uses fluoroscopy, with or without ultrasonography, to guide access to vessels and various lumens for the delivery of specific materials (stents, chemotherapy agents, embolization particles) for diagnostic and therapeutic purposes. These modalities are being employed for numerous endourologic procedures in veterinary patients and have become very popular over the past 5 to 10 years.


This chapter briefly reviews the use of IR/IE in the management of various abnormalities of both the upper and lower urinary tracts of veterinary patients. The relatively high incidence of upper and lower urinary tract disease, combined with the invasiveness and morbidity associated with traditional surgical techniques, makes the use of minimally invasive procedures appealing. Such endourologic procedures are considered the standard of care in human medicine, a trend that is occurring in veterinary medicine as well. There are many advantages to IR/IE techniques compared with traditional therapies. As a minimally invasive alternative, IR/IE contributes to reduced perioperative morbidity and mortality, shorter anesthesia times, and shorter hospital stays. In addition, some procedures provide treatment or palliation for diseases for which previously there were no good therapeutic alternatives (e.g., ureteral stenting or a ureteral bypass device for ureterolithiasis or ureteral strictures and palliative stenting for malignant urethral or ureteral obstructions). The main disadvantages are that these procedures are technically challenging, require expensive specialized equipment, and are routinely available in only a small number of institutions around the world. Furthermore, appropriate training in IR/IE is essential and the learning curve can be steep.



Equipment


Most IR/IE procedures are performed in a clean angiography or endoscopy suite with fluoroscopy. A traditional fluoroscopic unit often is sufficient, but a C-arm unit has the advantage of mobility, permitting imaging in multiple tangential views. Occasionally, ultrasonography is useful to guide percutaneous needle access into vessels or other structures (e.g., renal pelvis, urinary bladder).


Various flexible and rigid endoscopes are used for IE procedures. Rigid cystoscopy is commonly performed in female animals for urethral, bladder, and ureteral access. Recommended endoscope diameters (at the tip) range from 1.9 to 4 mm, depending on the size of the patient. Flexible ureteroscopes are used for urethral and bladder access in male dogs (2.5 to 2.8 mm) and for ureteral access in animals large enough to accept such diameters (>15 kg). Rigid nephroscopes are needed (5.3 to 7.3 mm) for percutaneous nephrolithotomy (PCNL) procedures. Different types of intracorporeal lithotriptors and lasers are available for various IE procedures such as ultrasonic, electrohydraulic, pneumatic, shock wave, and holmium: yttrium-aluminum-garnet (holmium:YAG) lithotriptors, and the diode-type laser (see Web Chapter 70). In addition, an arsenal of catheters, wires, stents (both metallic [urethral] and polyurethane [ureteral]), and baskets are useful for the varied patient population in veterinary practice. A subcutaneous ureteral bypass (SUB) device is now more commonly used for the treatment of feline ureteral obstructions. This is a nephrostomy catheter and a cystostomy catheter that are attached subcutaneously to a shunting port that allows urine to drain directly from the kidney to the bladder, without the need to salvage the ureter.



Kidney and Ureter



Interventional Approach to Nephrolithiasis


The direct treatment of nephroliths is necessary only when they become problematic, which is the case less than 10% of the time in the authors’ experience. Nephroliths are considered problematic when one of the following occurs: recurrent urinary tract infections (despite administration of appropriate antibiotic therapy for >8 to 12 weeks), pyelectasia or hydronephrosis, worsening renal function, pain and discomfort, or resulting intermittent ureteral obstruction. Traditional open surgical options to treat problematic nephroliths (e.g., nephrotomy, nephrectomy) are associated with frequent complications and high long-term morbidity. In a clinical study of dogs, approximately 43% had stone fragments remaining after surgery and 23% had procedure-related complications (Gookin et al, 1996). Additionally, 67% of dogs had evidence of renal azotemia that developed following nephrectomy. In a feline study of normal cats there was a 10% to 20% decrease in the glomerular filtration rate of the kidney in which a nephrotomy was performed (King et al, 2006). It is important to realize that in healthy animals the renal hypertrophic mechanisms are still functional, but in clinically affected dogs and cats this process already has been exhausted, which makes the change in renal function more dramatic. The use of less invasive approaches, such as extracorporeal shock wave lithotripsy (ESWL) (for stones of <1.5 to 2 cm) or PCNL (for stones of >1.5 to 2 cm), has been shown to be associated with preservation of renal function in humans. PCNL is highly effective in removing all stone fragments in the calices and does not require cutting of the nephrons. Instead, tissues are spread apart with the use of a balloon dilation kit to allow an endoscope and intracorporeal lithotriptor to remove the stone debris effectively.



Extracorporeal Shockwave Lithotripsy


ESWL is a minimally invasive alternative for the treatment of small calculi in the renal pelvis or ureters. ESWL uses external shock waves that pass through a water medium (either a wet or dry unit) and the soft tissue of the patient. The shock waves are directed under fluoroscopic guidance. The stone is shocked anywhere from 1000 to 3500 times at different energy levels for implosion and powdering of the stone. The debris is then permitted to traverse the ureter into the urinary bladder over a 2- to 12-week period. ESWL is believed to be very safe for the kidney, although subclinical intrarenal hemorrhage does occur. The severity of the damage is dose dependent. Studies have shown minimal to no decreases in glomerular filtration rate both short and long term after ESWL in patients with kidney stones. Availability of ESWL is limited, however. For stones of larger sizes (>1.5 to 2 cm), PCNL often is recommended in both humans and veterinary patients alike (see next section).



Percutaneous Nephrolithotomy


In humans, PCNL is considered the standard of care for nephroliths or proximal ureteroliths too large to be treated with ESWL or laser lithotripsy (>1.5 to 2 cm). PCNL also has been performed successfully in clinical veterinary patients. This procedure has been shown to have minimal or no negative effect on renal function in both children and adults with large stone burdens, solitary kidneys, or renal insufficiency. This minimally invasive endoscopic procedure allows access to the renal pelvis through a small sheath that is placed under fluoroscopic guidance (Figure 195-1). Once a tract is made into the renal pelvis, a nephroscope and intracorporeal lithotrite are used for stone fragmentation and removal. The aim is to minimize morbidity and preserve as much renal function as possible while removing all stone fragments to prevent the development of a ureteral obstruction and progressive renal insufficiency. The success rate of PCNL has been documented at 90% to 100% in both the adult and the pediatric human populations, and the authors have experienced the same in veterinary patients.




Interventional Approach to Essential Renal Hematuria


Essential (idiopathic) renal hematuria is a rare condition in which a focal area of bleeding in the upper urinary tract results in long-term hematuria, iron deficiency anemia (if chronic) and the potential for clot formation, or blood calculi. In people, any hemangioma, angioma, or vascular malformation present may be visualized ureteroscopically and subsequently cauterized via ureteroscopy. Idiopathic renal hematuria is diagnosed most commonly in very young large-breed dogs and occurs bilaterally in 25% to 33% of affected patients. For unilateral disease, usually confirmed by cystoscopy, ureteronephrectomy was previously recommended to minimize blood loss. Currently, nephrectomy should be considered contraindicated because of the risk of progressive bilateral disease and the availability of kidney-sparing techniques.



Ureteroscopy


It is possible to perform ureteroscopy in dogs larger than approximately 15 kg for visualization of renal hemorrhage. This procedure is challenging to perform in dogs because the canine ureter typically is less than 2 mm in diameter and the smallest ureteroscope currently available is approximately 2.5 mm in diameter. Ureteral access is obtained via cystoscopy; a guidewire is advanced up the ureter into the renal pelvis and the endoscope is advanced over the guidewire under fluoroscopic and endoscopic guidance (Figure 195-2). The ureteral and renal pelvic mucosa are examined; if a bleeding lesion is identified, electrocautery can be applied endoscopically to stop the bleed.




Sclerotherapy


The use of silver nitrate and povidone-iodine as cauterizing agents is an alternative method for mitigating upper urinary tract bleeding. This can be done in any dog (male or female), regardless of size. Under cystoscopic and fluoroscopic guidance, the cauterizing agent is infused into the renal pelvis through a ureteral occlusion balloon catheter. In a recent study in which sclerotherapy was used for the treatment of IRH complete cessation of macroscopic hematuria occurred in 4 of 6 dogs within a median of 6 hours (range, postoperative to 7 days). Two additional dogs improved, one moderately and one substantially. None of the dogs required nephrectomy. Ureteroscopy for electrocautery has only been performed in a small number of patients, and this is typically reserved for patients that have failed sclerotherapy. There were no complications noted from the procedure when a stent was placed postinfusion.

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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Interventional Strategies for Urinary Disease

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