Introduction

Urinary tract foreign bodies have been infrequently reported in the veterinary literature, with previous studies describing retrograde transurethral migration of vegetal material^1,2,3 and transenteric migration of foreign material into the urinary bladder.⁴ Although reports are lacking, the clinical experience of the authors is that implanted devices, including urinary catheters, are regularly damaged after patient-induced trauma, with resultant fragments developing into foreign bodies. Furthermore, ureteral stents are increasingly placed in a minimally invasive manner for treatment of urinary tract disease and may migrate or require removal.^{5,6,7,8,9,10,11,12,13,14}

Historically, traditional surgical techniques were often required to remove urinary tract foreign bodies and to replace or reposition medical implants. Minimally invasive endoscopic retrieval of intraluminal foreign bodies has also been used for retrieval and repositioning of urinary tract foreign bodies and implants. Limitations of cystoscopy in small animals include availability of equipment and patient size. Complications of cystoscopic interventions in dogs and cats can include trauma to the urethral bladder mucosa, transient urethritis, urethral perforation, and bladder rupture.¹³ Additionally, expertise is required to successfully perform cystoscopy, and associated costs can be excessive in some cases. As access to equipment and imaging technologies (such as fluoroscopy) have advanced in veterinary medicine, novel minimally invasive treatment options have become available. As such, some cases of urinary tract foreign bodies or malpositioned implants may be better treated with novel minimally invasive options, compared with traditional management strategies.

Endovascular snare systems are designed for retrieval and manipulation of foreign objects within the cardiovascular system or hollow organs with fluoroscopic guidance. These snare systems have been used in humans for retrieval of vascular foreign bodies (eg, catheter fragments, guidewires, stents, and sheath fragments)¹⁵ and for ureteral stent removal.^16,17,18 Benefits of this system include minimal periprocedural discomfort, ease of retrieval, and short procedural time.^{16,17,18,19,20,21,22} Use of fluoroscopic-guided snare devices has been described in veterinary cases for the retrieval of intravascular foreign bodies.^23,24,25

To the authors' knowledge, the use of an endovascular snare device for manipulation or retrieval of objects within the urinary tract has not been reported in veterinary medicine. The objectives of the study presented here were to report the removal or repositioning of urinary tract medical implants in dogs and cats by use of an ESS under fluoroscopic guidance and to report the procedural usefulness and complications in dogs and cats undergoing these procedures.

Materials and Methods

Procedures

Four categories of procedures that included use of the ESS to manage urinary tract implants were performed, including transurethral retrieval of vesicourethral implants, transurethral stent repositioning, transnephric stent retrieval, and cystoscopic-assisted transureteral ureteral stent retrieval. Fluoroscopic guidance was used for all procedures. In all procedures, the orientation of the repositioned or retrieved foreign body was optimized for atraumatic retrieval, and the course of the ESS and retrieved or repositioned implant was visualized fluoroscopically for the duration of each procedure.

Transurethral retrieval of vesicourethral implants—Patients were placed in either left or right lateral recumbency. The urethra was intubated with a 0.035-inch × 180-cm hydrophilic guidewire,^a and the guidewire was passed retrograde from the urethra into the bladder. In each case, the wire was passed until it coiled within the bladder. A 6F to 7F introducer sheath and dilator combination^b was introduced into the urethra over the hydrophilic guidewire, and a snare catheter (6F to 7F)^c was passed retrograde over the guidewire (through the sheath) until it was beyond the trigone and seated within the bladder or urethra. The catheter was held in place while the guidewire was removed. Multilooped snares^c of various loop diameters were passed retrograde through the snare catheter until the snare emerged from the snare catheter with loops fully deployed. The multiple loops were passed over the implant or foreign material, and once engaged, the snare catheter was passed over the loops and snare wire to close down the loop width and secure the implant within the device (Figure 1). The snare wire and catheter were withdrawn as 1 unit, and tension on the 2 devices was maintained to prevent the foreign body from dislodging (Figure 2). The fluoroscopy unit was moved as needed to visualize the removal of the foreign body or ureteral stent and snare wire–catheter device antegrade from the urethra.

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Fluoroscopic images of the removal of a urinary bladder foreign body by use of an ESS in a 5-year-old castrated male Chihuahua. A—The foreign body (asterisk) can be seen within the urinary bladder, and a hydrophilic guidewire (plus sign) has been introduced to allow for placement of the snare catheter. B—The snare catheter (arrowhead) is present within the urinary bladder, and the snare has been introduced into the snare catheter after removal of the guidewire. C—The snare has been deployed into the urinary bladder and will be manipulated until the foreign body (asterisk) is engaged within the snare loops. D—The snare has been pulled into the snare catheter after engaging with the foreign body (asterisk) to lock the foreign body in position.

Citation: Journal of the American Veterinary Medical Association 258, 9; 10.2460/javma.258.9.983

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Transurethral ureteral stent repositioning—The patients were placed in lateral recumbency, and a hydrophilic safety guidewire (0.035 inches × 260 cm)^a was already in place from the percutaneous stent placement, over which a 6F introducer sheath and dilator^d were seated into the distal portion of the ureter as previously described.²⁶ A second guidewire was passed into the sheath and into the ureter; the sheath was then removed from both guidewires and replaced over the second guidewire. Once the sheath was in place, a snare catheter^c was passed through the sheath over the guidewire and into the ureter. Once the snare catheter was seated, it was held in place while the guidewire was removed antegrade. A multilooped variable diameter snare^c was passed retrograde through the snare catheter and was deployed in the distal portion of the ureter. With fluoroscopic guidance, the multilooped snare was passed over the distal pigtail of the malpositioned ureteral stent. Once the snare engaged the stent, the snare catheter was passed over the snare wire to decrease the loop width and secure the ureteral stent within the device.

The snare wire, catheter, and entrapped pigtail of the stent were pulled caudally as a single unit until the distal pigtail of the stent was appropriately positioned in the bladder. The stent was then released from the snare by pushing the snare out of the snare catheter and loosening the snare loops. Fluoroscopic assessment confirmed appropriate stent positioning.

Transnephric ureteral stent retrieval—Patients were placed in dorsal recumbency, and transnephric ureteral stent retrieval was performed percutaneously (1 dog) or via a standard midline laparotomy (1 dog and 1 cat). Percutaneous ultrasound guidance²⁶ or open access to the renal pelvis was gained as previously described. Following the passage of an 0.018- or 0.035-inch hydrophilic guidewire^a to coil several loops within the renal pelvis, a 6F or 7F introducer sheath and dilator^b were inserted over the guidewire and into the renal pelvis; the dilator was subsequently removed. With fluoroscopic guidance, a snare catheter (3.2F, 6F, or 7F)^c was introduced into the renal pelvis over the guidewire and the guidewire was removed. A multilooped snare (2- to 4-mm-diameter, 6- to 10-mm-diameter, or 12- to 20-mm-diameter loops)^c was passed into the renal pelvis through the snare catheter, and the snare was deployed so that the loops were expanded. The snare was passed onto the proximal pigtail of the ureteral stent, and the snare catheter was passed antegrade over the loops and snare wire to close down the loop width and secure the ureteral stent pigtail within the device (Figure 3). The locked snare device and ureteral stent were removed as 1 unit through the introducer sheath.

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Image depicting the interaction between a snare catheter (arrowhead), snare (arrow), and ureteral stent (asterisk) prior to tightening the snare loops around the pigtail of a ureteral stent before removal.

Citation: Journal of the American Veterinary Medical Association 258, 9; 10.2460/javma.258.9.983

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Fluoroscopic (A through C) and intraoperative (D) images of a 6-year-old castrated male domestic shorthair cat undergoing transnephric ureteral stent removal. A—An 18-gauge over-the-needle catheter (star) has been inserted into the renal pelvis, and nephropyelography has been performed. The ureteral stent can be seen extending from the renal pelvis into the ureter (asterisk). B—A 0.035-inch guidewire (plus sign) has been inserted into the renal pelvis and advanced into the proximal portion of the ureter. C—A snare catheter (arrowhead) has been inserted into the renal pelvis, and the snare has been deployed in an attempt to engage the ureteral stent. D—Intraoperative image of the kidney (K) with the insertion site (arrow) for the equipment visible on the greater curvature of the kidney.

Citation: Journal of the American Veterinary Medical Association 258, 9; 10.2460/javma.258.9.983

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Cystoscopic-assisted transureteral ureteral stent retrieval—The patient was placed in dorsal recumbency, and a cystoscope was introduced into the urethra and used to visualize the ureteral orifice of interest. A hydrophilic guidewire (0.035 inches × 180 cm)^a was passed retrograde into the ureter and renal pelvis to the location of a migrated stent; the guidewire was passed until it was coiled within the renal pelvis (Figure 4). The cystoscope was removed over the guidewire, and a 6F snare catheter was passed retrograde up the guidewire and into the renal pelvis. Following removal of the guidewire, a multilooped snare^c with 18- to 30-mm-diameter loops was passed retrograde through the snare catheter until the snare emerged from the snare catheter with loops fully deployed. The multiple loops were passed over the ureteral stent, and once engaged, the snare catheter was passed over the snare wire and loops to decrease loop width and secure the ureteral stent within the device. The snare wire and catheter were withdrawn as 1 unit, maintaining tension on the 2 devices to prevent the foreign body from dislodging. The fluoroscopy unit was moved as needed to visualize the removal of the ureteral stent and snare wire–catheter device antegrade from the urethra.

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Fluoroscopic images from a 3-year-old spayed female Newfoundland undergoing cystoscopic-assisted transureteral ureteral stent removal. A—The entire ureteral stent (asterisk) can be seen within the renal pelvis after retrograde movement, and a hydrophilic guidewire (plus sign) has been introduced to allow for placement of the snare catheter (arrowhead). B—The snare has been deployed into the renal pelvis, and an attempt is being made to snare the ureteral stent pigtail. C—The ureteral stent has been engaged in the snare and can be seen midureter after partial removal with the ESS.

Citation: Journal of the American Veterinary Medical Association 258, 9; 10.2460/javma.258.9.983

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Results

Discussion

An ESS was used successfully for removal or repositioning of urinary implants, including ureteral stents or retained urinary catheters for 18 procedures in 14 dogs and 3 cats. The device allowed for a quick, minimally invasive solution, thereby avoiding nephrotomy, ureteromy, and cystotomy. No patients developed any known complications associated with use of the ESS, further supporting this as a safe alternative to more invasive procedures.

Transurethral retrieval of urinary catheter fragments and ureteral stents was the most common procedure performed, followed by transurethral repositioning of ureteral stents, transnephric retrieval of ureteral stents, and cystoscopic-assisted transureteral stent retrieval. The usefulness of ureteral stents in small animals is comparable to humans, for which indwelling ureteral stents have been placed for the purpose of temporary or permanent relief of ureteral obstruction secondary to benign or malignant obstruction or following management of primary genitourinary disease.^{5,6,7,8,9,10,11,12} Complications of indwelling ureteral stents in humans have been documented to occur in as many as 80% to 90% of patients and include lower urinary tract signs, recurrent infection, migration, malposition, encrustation, obstruction, and fracture.²⁷ Inevitable replacement or removal of ureteral stents in humans has warranted investigation into minimally invasive methods of retrieval. Historically, endoscopic retrieval has been the standard of care, although the requirement for deep sedation and local or general anesthesia as well as increased discomfort to the patients associated with cystoscopy have motivated a search for alternative approaches. More recently, fluoroscopic-guided snare retrieval has been reported with success in human medicine.^{16,17,18,20,21,22}

Reports of ureteral stent replacement or removal in veterinary patients are uncommon. In a study²⁸ of dogs with ureteral stents in place for treatment of benign obstructions, stent removal or replacement was reported in up to 16% of patients and reasons for removal or replacement included stent obstruction, migration, or recurrent infection.²⁸ In previous studies,^7,29 cats that underwent ureteral stent placement for benign ureteral obstruction had a documented stent exchange rate ranging from 27% to 44% as a result of stent occlusion, uroabdomen, or severe refractory cystitis and lower urinary tract signs. The common occurrence of these complications requires the evaluation of additional techniques for stent removal or replacement. Fluoroscopic-guided retrieval of ureteral stents without adjunctive endoscopy has been performed in human medicine because of the advantages of reduced procedural time and improved patient comfort.^{16,17,18,19,20,21,22} It is the authors' opinion that the benefits to the patients of the present study are similar to those reported in human medicine. In addition, some veterinary patients may be too small for cystoscopy.

In the patients of the present study, all retained vesicourethral implants were urinary catheter fragments. In these patients, urinary catheters had been placed for management of a primary neurologic or urinary disorder, and catheters were damaged secondary to patient-induced trauma with subsequent retrograde migration into the urinary bladder.

Minimally invasive retrieval of stents or retained vesicourethral implants in small animals has traditionally been performed with cystoscopy³⁰; however, patient size limitations, equipment availability, and lack of necessary expertise have required the need to pursue open surgical procedures. The techniques described in the present study provided an alternative minimally invasive approach for management of malpositioned urinary tract implants, which can be applied to almost any dog or cat. It should be mentioned that a subset of these patients may have undergone procedures performed successfully with either endoscopy or fluoroscopic-guided ESS, and the decision to pursue retrieval with the ESS was clinician dependent.

Additionally, percutaneous transnephric ureteral stent retrieval may be an alternative to open transnephric retrieval, both of which were successfully demonstrated within our patient population. Limitations that might prohibit application of this technique to all veterinary patients may include the price of equipment (although the cost is less than that of traditional surgery or endoscopy), necessary expertise, and small size of some patients.

Although snare retrieval of ureteral stents has been reported in the human literature, to the authors' knowledge, ESS retrieval of retained vesicourethral implants has not been previously reported in the veterinary literature. Endovascular foreign body retrieval with snare devices has been previously described,²³ although infrequently. Published reports include a case series of intravascular foreign bodies retrieved with an endovascular snare in 5 dogs, 1 goat, and 1 horse,²⁴ as well as successful endovascular snare retrieval of migrated jugular vein catheters in 3 dogs.²⁵ In both reports,^24,25 a goose-necked single loop snare wire and catheter were used. One of the unique advantages of this system is the 90° orientation of the snare loop to the wire body when deployed from the catheter, allowing retrieval of linear objects that exist parallel to the lumen. A multilooped snare^c was employed for use within the urinary tract in all patients of the present study for several potential advantages, including the capture of nonlinear structures such as pig-tailed devices. Additionally, the multilooped ESS may have had an increased success rate (compared with a single loop wire) as a result of the urinary tract's varied and often larger luminal diameter, such as what is encountered in the urinary bladder.

An advantage of the ESS is the wide range of sizes available. Snare catheters are available in 3.2F, 6F, and 7F, with corresponding wire loop diameters ranging from 2 to 4 mm up to 27 to 45 mm. The versatility in catheter size and loop diameter is suitable for veterinary use given the wide range of patient sizes, as exemplified by successful use of the device in the dogs and cats of the present study. The patients in which the smallest systems were used included a dog and cat that underwent transnephric ureteral stent retrieval, for which working space within the renal pelvis was presumably limited. On the basis of the outcomes and patient sizes reported, snare loop diameters ranging from 12 to 20 mm to 18 to 30 mm are appropriate for most dogs and cats for manipulation of retained implants or malpositioned ureteral stents. The use of smaller snare loop diameters (2 to 4 mm and 6 to 10 mm) and associated catheters may be necessary within the renal pelvis or ureter or when trying to grasp a foreign body in the urethra, although the successful use of a snare wire loop diameter of 12 to 20 mm in the renal pelvis of 1 patient suggested a wide range of usefulness in veterinary patients.

In the present study, all patients that underwent stent retrieval with the ESS required general anesthesia, whereas 4 of 7 patients that underwent retained vesicourethral implant retrieval required general anesthesia. The minimally invasive nature of the snare device procedure and associated short procedural time allow for sedation and not general anesthesia in many affected patients; this is an advantage over open surgical and endoscopic techniques and further reduces total costs. Sedation, rather than general anesthesia, should be considered when removing retained vesicourethral implants with the snare system, unless contraindications exist including anticipated extended procedure time or individual patient risk factors such as compromised laryngeal function.

In the present study, 3 animals underwent ureteral stent repositioning transurethrally (n = 2) or transnephrically (1). All 3 procedures were secondary to a primary procedure during which inappropriate ureteral stent positioning occurred. The successful manipulation or retrieval of ureteral stents from the distal portion of the ureter and renal pelvis within the reported cohort suggests that this technique may be used to troubleshoot inappropriately placed devices within the urinary tract.

In the present study, the successful performance of transnephric snare retrieval of an inappropriately sized ureteral stent in 1 cat, fractured stent in 1 dog, and migrated stent in 1 dog demonstrated the potential usefulness of this technique in small animals of almost any size. Perhaps more important than patient size is the size of the renal pelvis, which must allow for enough working space for the introducer sheath and dilator and the snare catheter and wire as well as for manipulation of these devices. A 3.2F, 6F, and 7F catheter were used to access the renal pelves in the 2 dogs and cat of the present study; the authors suggest that catheter size be selected on the basis of patient size and renal pelvic diameter. Percutaneous ultrasound-guided transnephric ureteral access has been previously described for the purpose of placing ureteral stents,²⁶ and this method of access was successfully performed in 1 dog, although ESS retrieval of ureteral stents from the renal pelvis remains novel. Additionally, cystoscopic-assisted transureteral renal pelvis access for retrieval of a migrated ureteral stent in a single patient demonstrated another method of accessing the renal pelvis without requiring an open approach. Cystoscopy in small animals is limited by patient size as well as access to appropriate equipment and expertise, which should be considered prior to attempting removal of ureteral or renal foreign bodies.

One procedural complication was reported in the present study. This complication occurred during the attempted retrieval of a retained vesicourethral implant in a male dog. The implant, which had been secured within the ESS, became dislodged at the pelvic flexure on withdrawal. The stability of the interlocked snare device requires close association of the snare wire to the catheter, which is maintained by countertension between the snare and catheter. Suboptimal tension by the operator likely led to loss of this connection with resultant dropping of the implant in the distal portion of the urethra before removal. Maintaining appropriate tension and optimizing the grasp on the body or ends of implants that are being retrieved is likely a comparable challenge for cystoscopic retrieval of ureteral implants or stones, and additional case numbers would be helpful in comparing procedural complications and outcomes between the 2 approaches. The longer path of the male urethra and relatively narrow lumen may have also played a role in this technical complication. The pliable nature of the retained vesicourethral implants within this cohort allowed the implants to be grasped at the tip or midbody, leading to folding and compression within the snare catheter and urethra at the time of withdrawal. The authors suggest that attempting to grasp the midbody of comparably pliable vesicourethral implants may be a more reliable method of grasping and withdrawing it, as opposed to grasping the end or tip of a retained implant; the size and position of a retained vesicourethral implant relative to bladder and urethral size may not allow for such precise positioning of the snare in some instances.

Some limitations should be recognized. The implant that is to be removed or manipulated must be radiopaque and of appropriate size to allow for adequate visualization and retrieval through a transnephric or transurethral approach. Additionally, the implant to be retrieved should be flexible and pliable enough to allow for safe, atraumatic retrieval. Fluoroscopy was used in all procedures and was considered necessary in the patients for which ESS manipulation of retained urinary implants was performed in conjunction with additional fluoroscopic-guided procedures. The exposure of clinicians and patients to radiation during fluoroscopic-guided ESS retrieval for retained implants, as a stand-alone procedure, may be avoided if alternative methods of retrieval such as cystoscopy are used. This should be considered in all patients undergoing these procedures. Procedural duration was not available in the subset of cases undergoing transnephric retrieval of ureteral stents or transurethral stent repositioning and therefore could not be compared with alternative approaches. Finally, the present study included a relatively small number of patients, and long-term outcomes were not reported; therefore, the morbidity incurred by patients from this technique may have been underappreciated.

In conclusion, within the cohort of the present study, transurethral and transnephric manipulation or retrieval of medical implants from the renal pelvis, ureter, bladder, or urethra by use of a fluoroscopic-guided, multilooped snare wire and catheter system was feasible and successfully performed in all patients. The success of this procedure is contingent on clinician comfort and skill with fluoroscopic-guided techniques, and appropriate patient selection is essential. Finally, this technique may avoid additional cost, morbidity, or time incurred by open or endoscopic approaches.