Following the description of percutaneous arterial catheterization by Seldinger in the 1950’s, angiography developed into a widely-utilized and essential diagnostic tool in human medicine. Technological advances have since helped transform this diagnostic modality into a sub-specialization with enormous therapeutic potential. Interventional radiology (IR) involves the use of contemporary imaging techniques such as fluoroscopy and specialized equipment such as catheters, guidewires, and stents for therapeutic purposes. The field has grown considerably over the past 20 years and IR techniques are considered the gold standard to treat a variety of conditions in humans.
Despite applications in veterinary medicine, IR techniques have not been widely adopted. Examples in the veterinary literature include coil embolization to treat patent ductus arteriosus, stenting for tracheal collapse, coil embolization of the carotid and maxillary arteries for treatment of hemorrhage from guttural pouch mycosis in horses, and coil embolization of canine intrahepatic portosystemic shunts.
Advantages and Disadvantages
The use of IR techniques in veterinary patients offers a number of advantages to more traditional therapies. These procedures are minimally invasive and can therefore lead to reduced peri-operative morbidity and mortality, shorter anesthesia times and shorter hospital stays. Some less equipment-intensive procedures can result in reduced costs as well. In addition, some techniques such as chemoembolization of tumors or palliative stenting for malignant obstructions offer treatment options for patients with various conditions that may not be amenable to standard therapies or when the standard-of-care treatments are associated with excessive morbidity, cost, or poor outcome.
The primary disadvantages of IR include the required technical expertise that is not part of traditional veterinary training, the specialized equipment necessary (fluoroscopy with or without digital subtraction capabilities), and the initial capital investment necessary to provide a suitable inventory of catheters, guidewires, balloons, stents and coils.
Equipment and Technique
As most of these procedures are minimally-invasive (performed through natural orifices or small holes in the skin), traditional sterile operating rooms are not required, but recommended. Most of these procedures are performed in clean angiography suites. The entry sites receive a traditional sterile scrub, and operators wear full lead gowns, lead thyroid shields, caps, gowns, and masks. The radiation exposure during these procedures can be minimized by following well delineated ALARA (“As Low As Reasonably Achievable”) guidelines. The operator should review radiation safety protocols that discuss minimizing exposure time, proper collimation, source to image distance, and shielding.
For many of the more commonly performed IR procedures, a traditional fluoroscopy unit is sufficient. A C-arm fluoroscopy unit has the advantage of mobility of the image intensifier permitting multiple tangential views without moving the patient. Occasionally, ultrasonography is useful for percutaneous needle access into vessels or other structures. Digital subtraction angiography (DSA) and “road-mapping” are specialized, computer software, imaging techniques based on fluoroscopy that allow high resolution images to be obtained with minimal use of contrast agent which is often a concern in our relatively small veterinary patients. DSA is required for super-selective angiograms of small caliber vessels and those vessels in the head (or where there is substantial overlying bone that makes visualization difficult).
Before performing these procedures, the operator should be familiar with basic IR equipment including guidewires, dilators, vascular sheaths/introducers, angiography catheters, stents, and embolic agents. There is an abundance of information available through various medical textbooks although little information currently exists in the veterinary literature.
Endoscopy, in combination with fluoroscopy, can be used for various minimally invasive interventions as well. This modality is termed interventional endoscopy (IE). Some examples include endoscopic ureteral stenting, percutaneous nephrolithotomy (PCNL), cystoscopic-laser ablation (CLA) of ureteral ectopia, and endoscopic retrograde cholangiopancreatography (ERCP) with biliary stenting. These endoscopic procedures are facilitated by the use of fluoroscopy to aid in the guidance of an assortment of guidewires, catheters and stents. The various endoscopes used include, but are not limited to, the following types: rigid cystoscopes (ranging in size from 1.9 mm to 7mm diameter), flexible ureteroscopes (ranging in size from 2.7-3.4 mm diameter), nephroscopes (5.3-7.3 mm), and side-view duodenoscopes (7.5-11 mm diameter).
Interventional Endoscopy (IE) involves the use of endoscopic equipment with other contemporary imaging modalities, such as fluoroscopy and/or ultrasound, to perform diagnostic and therapeutic procedures in virtually any part of the body accessed endoscopically (gastrointestinal, biliary, respiratory, urinary tract, etc).
Currently, an expanding investigation of the use of some novel techniques in veterinary medicine has been undertaken. The combination of endosocpy and fluoroscopy allows for one to visualize and gain access into small orifices that would otherwise require more invasive surgical technique. A good example of this is the placement of a biliary stent into the common bile duct via the major duodenal papilla with endoscopic and fluoroscopic guidance. Many of these interventional procedures are considered the standard-of-care in human medicine, and are currently being investigated in veterinary medicine. The use of these techniques are expanding as these modalities are becoming more widely available.
The invasiveness and morbidity associated with some traditional surgical techniques (i.e. biliary re-routing surgery, ureterotomy for ureteral obstructions, or nasopharyngeal surgery for nasopharyngeal stenosis) makes the use of minimally invasive alternatives using IE appealing. The advantages of such procedures are the minimally invasive nature, the lower morbidity, shorter hospital stays, and sometimes even the lack of alternative options. The disadvantages are that these procedures are technically challenges, require specialized equipment, and require specialized training.
This talk is a brief overview of some of the minimally invasive interventional endoscopic procedures actively being performed in veterinary medicine as well as some promising future applications currently under investigation. A large number of the procedures we are currently performing are in the urinary tract (ureteral stenting, laser lithotripsy, urethral stenting, urethral bulking agent injections for incontinence, etc), and this will not be the focus of this discussion, as another session will focus on endourology.
- A C-arm fluoroscopy unit is ideal for most of the IE procedures we are currently performing. This unit has the advantage of mobility of the image intensifier, permitting various tangential views without moving the patient and positioning of the patient where endoscopy is easiest (i.e. at the end of the table for rigid cystoscopy). Ultrasonography is useful for percutaneous needle access into structures (gall bladder, renal pelvis, etc) making portable ultrasound very valuable. Guidewires of various size, shape, length, and stiffness, as well as catheters and stents of various materials, shapes, and sizes are needed for each procedure.
Endoscopes are used to guide the operator toward the orifice where visualization and access is needed (i.e. common bile duct, ureteral orifice, nasopharyngeal stenosis). Various flexible and rigid endoscopes are used for interventional endosurgical techniques. Flexible gastroduodenoscopes (6 mm and 8 mm), bronchoscopes, and ureteroscopes (7.5-8.2 french) are classically used for various body system interventions. Rigid endoscopes (1.9-7.5 mm) are also useful for cystoscopy and rhinoscopy. An adult (11 mm) or pediatric (9mm) side-view duodensocope is necessary for endoscopic retrograde cholangiopancreatography (ERCP) and biliary stenting. Other specialized catheters and guidewires are needed for the particular procedure (see presentation).
Nasopharyngeal stenosis (NPS) is a pathologic narrowing within the nasopharynx caudal to the choanae resulting in a variable degree of inspiratory stertor. This can occur as a congenital anomaly or be secondary to an inflammatory condition (aspiration rhinitis), surgery, trauma, or a space-occupying lesion. Traditional therapy involves surgery or serial balloon dilatation procedures. Balloon dilatation is minimally invasive and utilizes interventional technique via fluoroscopy and endoscopy, but can result in re-stricture in a few days to a few weeks. We have found that stenting of this nasopharyngeal region allows for a more permanent fixation and results in both dogs and cats have been extremely promising.
Under both fluoroscopic and rhinoscopic guidance a hydrophilic Weasel? guidewire is advanced caudally from the nares through the ventral nasal meatus, through the stenotic opening, and down the esophagus. This is viewed inside the nasopharynx with retroflex rhinoscopy, and from the outside with fluoroscopy. Once the stenotic lesion is identified a percutaneous transluminal angioplasty balloon, preloaded with a metallic stent (balloon expanded metallic stent—BEMS) is advanced over the guidewire and centered over the stenotic lesion. Using both fluoroscopic and endoscopic viewing the balloon is inflated (with a 50:50 mixture of contrast and saline) and the waist of the stenosis is subsequently broken with the balloon.
As the balloon expands, the stent deploys. Once the stenosis is open, the balloon is deflated and removed over the wire, and the stent is left to remain in place. The stent will re-epithelialize in a few weeks (approximately 2-6 weeks). The size (length and width) of the stent and balloon are chosen based on Computed Tomography (CT), which is done prior to the procedure. The patients usually go home the same day as the procedure with antifibrotic doses of gluococorticoids (prednisone 0.5 mg/kg), 2 weeks of antibiotics and tramadol as needed for any discomfort.
Tracheal stenting can per performed for a variety of reasons including tracheal neoplasia, tracheal stenosis, and most commonly tracheal collapse. At the University of Pennsylvania tracheal stenting is classically performed using fluoroscopic guidance alone, without the assistance of endoscopy. There are quite a number of veterinarians who perform tracheal stenting under tracheoscopic guidance making this interventional endoscopic (IE) procedure reasonably common. Tracheal stenting will be discussed for a full session so I will defer to that lecture for further details of this procedure.
Tracheal Foreign Body Retrieval
Tracheal foreign bodies are seemingly uncommon to encounter. When you do, having a fast, safe, and effective approach for retrieval is imperative. Most internists would use an endoscope and grasper or basket. In very small animals this requires extubation and a very small endoscope, which can result in hypoxia, hypercarbia and minimal or no ventilation. Using endoscopy with a retrieval basket, in conjunction with fluoroscopy, helps to guide you to the object and watch the wires entrap the prior to removing the basket. For radiolucent objects this would be done with endoscopy alone, but for radio-opaque material this can be easily done with a retrieval basket and fluoroscopy alone, directly through the endotracheal tube, preserving ventilation (see presentation) and foregoing the need for tracheoscopy.
Esophageal Balloon Dilation and Esophageal Stenting
Esophageal strictures are frustrating to treat for both veterinarians and physicians. Patients classically present with signs of regurgitation. Strictures in the esophagus can be secondary to reflex esophagitis (commonly post-anesthesia), caustic substance ingestion, medications sitting on the esophageal mucosa for lengths of time (i.e. doxycycline tablets in cats), from esophageal foreign bodies, etc. Many alternative therapies have been tried because recurrence is very common. Balloon dilation or bougienage procedures using endoscopic guidance is currently the treatment of choice in veterinary medicine.
Regardless of the intervention chosen, many of these strictures recur and present as a monetary and clinical dilemma for our feline and canine patients. In human medicine fluoroscopy, in conjunction with endoscopy, is used for dilation of esophageal strictures, allowing better visualization that the waist of the stricture is not just stretched, but completely broken. With a similar theory to the NPS cases, esophageal strictures would ideally be balloon dilated with a stent left in place to keep the stenotic lesion open for the time it would take the tissue to re-stenose. The biggest concern about doing this in the esophagus is that this area is very motile (vs the nasopharynx) and food will need to pass through the area.
The risk of the stent migrating into the stomach, or proliferative tissue growth around the ends of the stent material, makes permanent stenting for benign disease less than ideal. In order to circumvent these concerns pliable stents with a shape that would ideally hold up again peristalsis (dumb-bell and self expanding) have been tried. Knowing that the stenotic tissue will heal over 14 or more days, having a stent that can be removed or resorbed (polylactic acid or PDS stents) in a few months is being investigated. This has been studied in humans for some time and we too have now been intently investigating this option.
Using both fluoroscopic and endoscopic guidance, the stent is centered over the esophageal stenosis inside its delivery system. Once deployed the stent is expanded in place and tacked with a suture (either endoscopically or manually placed suture) to prevent stent migration into the stomach. The preliminary results thus far have been promising. In the future this may be a consideration at the time of 2nd or 3rd balloon dilation to avoid serial anesthetic procedures and high costs.
Esophageal-jejunal Feeding Tubes
Enteral methods of feeding are preferred over parenteral nutrition in humans due to the benefits on gut mucosal integrity, barrier function, and lower complication rates. Jejunal feeding in small animal patients is controversial. In animals that are intolerant of gastric feedings, have intractable vomiting, have pancreatitis where pancreatic exocrine duct by-pass is desired, or are unconscious and regurgitation or reflux is a concern (ventiled animals), feeding directly into the jejunum is recommended.
Classically this has been done via surgical or laparoscopic technique with a high complication and orad dislodement rates. Due to the ease of placing a nasal feeding tube or an esophagostomy feeding tube, tubes have been able to be placed into the jejunum from the nares (NJ) or esophagus (EJ) with fluoroscopy +/- endoscopy, eliminating the complications associated with septic peritonitis or unnecessary gastric or jejunal orifices. NJ and EJ tube placement is aided with fluoroscopy visualizing the guidewire and catheter placement into the duodenum and into the jejunum. If an upper GI endoscopic procedure is being performed at the same time (see pictures in presentation) than wire placement across the pylorus can be done through the endoscope. This technique is fast, effective and fairly inexpensive when compared to surgical placement and parenteral access and intensive care monitoring of TPN.
Colonic obstructions are rare in small animal patients. They can be due to neoplastic lesions, strictures, or granulomatous lesions. In humans, colonic stents have been available for over a decade and are most commonly placed for people with neoplasia who are a prohibitive surgical risk or resection holds little chance of surgical cure. They have been used as a mechanism to help deobstipate for bowel preparation prior to resection and anastomosis.
In humans, colonic stents can either be placed through the endoscope for direct visualization while they are deployed, or they can be placed over a guidewire under fluoroscopy alone. They are preferred to be placed through the scope for precise stricture localization, for proximal tumor locations and to guide the stent across acute angulations in the colon. In humans clinical success is seen in up to 95% of patients. At the University of Pennsylvania we have placed 4 colonic stents in cats to date; 3 for tumors and 1 for a stricture. In all cases colonoscopy was done to visualize the lesion and help localize the lesion fluoroscopically. A guidewire was then advanced through the stenotic lesion. Under fluoroscopic guidance a self-expanding metallic stent (SEMS) was placed across the stenotic lesion or tumor and the stent was deployed.
Patency was re-established immediately in all cases and subsequent deobstipation was achieved. All cats were fecally continent, and no stent migrations were seen. The stent was visualized to be incorporated into the colonic mucosa within 4 days in one cat that was re-scoped.
- Extrahepatic biliary obstructions present a great dilemma as they induce life-threatening metabolic derangements, causing excessive morbidity and mortality. Surgical treatment is often indicated, but the outcome with biliary re-routing surgery holds such a high risk, with the mortality rate ranging from 25-70% in dogs and over 75% in cats. If the metabolic derangements can be relieved by a fast and effective decompressive procedure than future surgical interventions for a more definitive fixation may be safer for the patient. We will discuss two options that can be performed in veterinary patients 1) endoscopic drainage through the common bile duct (ERCP) and 2) laparoscopic assisted biliary drainage by cholecystostomy tube placement.
Endoscopic Retrograde Cholangiopancreatotgraphy (ERCP) and Biliary Stent Placement
Endoscopic retrograde cholangiopancreatography (ERCP) is an IE technique used for the diagnosis, and potential treatment, of biliary tract disease, pancreatitis, or pancreatic obstructive lesions. To date biliary stents have been successfully placed in a small handful of normal purpose-bred dogs, and clinical investigation is underway. Using a side-viewed duodenoscope the major duodenal papilla is visualized and cannulated with a sphinctertome catheter. Once a retrograde cholangiogram and pancreatogram are performed a guidewire is advanced into the common bile duct under fluoroscopic guidance. Then, through the endoscope, a polyurethrane stent is advanced over the wire. With fluoroscopic and endoscopic guidance the stent is advanced into the common bile duct, transverses the major duodenal papilla and exits into the duodenum. This can be left in place until the obstructive lesion resolves (ie pancreatitis), or a permanent metallic stent can be used in the case of neoplasia. This bypasses the need for re-routing biliary surgery for EHBDO.
Laparoscopic Cholecystostomy Tubes
Laparoscopic cholecystotomy tubes have been reported in a small number of clinical veterinary patients. They can be accomplished with very short anesthesia times. An 8 or 10 french locking loop pig-tail catheter can be advanced through a right paracostal approach being visualized with laparoscopy. With transhepatic penetration with the catheter, the gallbladder is accessed. Once the trocar is into the lumen of the gallbladder, as visualized via laparoscopy, the trocar and stylette are slowly removed and the locking loop mechanism is set in place. The catheter can drain the gallbladder and can be sutured securely to the body wall. This can remain in place until the patient is a better anesthetic candidate for surgery, or for 4—6 weeks while a seal is achieved and a more benign lesion resolves (pancreatitis), bypassing the need for surgical intervention.
Urinary Techniques – Kidney & Ureter
Ureteral stenting is performed for a variety of disorders to divert urine from the renal pelvis into the urinary bladder. This technique can be useful in patients with ureteral obstruction and due to ureterolithiasis, ureteral or trigonal obstructive neoplasia, following ureteroscopy, percutaneous nephrolithotomy, ureteral stone retrieval (basket retrieval or via laser lithotripsy), for post-operative ureteral anastomosis, ureteral tears, ureteral spasm, or ureteritis. In addition, the presence of the ureteral stent may result in subsequent passive ureteral dilation to permit passage of previously obstructive ureteroliths, or allow passage of the flexible ureteroscope for appropriate ureteral intervention. This technique is currently under investigation for use in veterinary patients with ureterolith-induced obstructions, particularly in cats (Figure 1). Ureteral stenting is also ideal in patients with nephroliths or ureteroliths that are undergoing ESWL to aid in fragment passage following treatment.
Percutaneous Nephrolithotomy (PCNL)
Nephrolithiasis or proximal ureteral obstructions secondary to ureteroliths can result in progressive renal insufficiency, intractable pyelonephritis, ureteral colic, and hydronephrosis. If the stone is small enough it may pass, however others require surgery to relieve the obstruction or avoid permanent nephron damage. Nephrotomies, pyelotomies or ureterotomies can be prolonged, invasive, and complicated surgeries, potentially resulting in significant morbidity. In people, percutaneous nephrolithotomy is considered the standard-of-care for nephroliths too large to be treated with ESWL or retrograde ureteroscopy with laser lithotripsy, and has recently been performed successfully in clinical veterinary cases. This minimally invasive procedure aims to minimize morbidity, and preserve as much renal function as possible.
Percutaneous Nephrostomy Tube Placement
Ureteral obstructions secondary to ureteroliths or malignancy can result in severe hydronephrosis and/or life-threatening azotemia when present bilaterally or in animals with concurrent renal insufficiency. Some patients can be managed with supportive care until a ureterolith passes, others may require surgery to avoid permanent damage and/or hemodialsysi to stabilize the patient prior to a prolonged anesthesia. Ureterotomies can be relatively prolonged and complicated surgeries in these often debilitated patients. One possibility is to place a nephrostomy tube percutaneously in order to quickly relieve the obstruction, and determine whether adequate renal function remains before prolonged anesthesia for ureteral surgery is performed.
Cystoscopic-Guided Ectopic Ureter Laser Ablation
Ectopic ureters are a common congenital anatomic deformity in dogs with the ureteral orifice being positioned distal to the bladder trigone within the ureter, vagina, vestibule or uterus. Over 95% of dogs with ectopic ureters transverse intramurally and are candidates for the minimally invasive procedure. Endoscopic repair of ectopic ureters is a common procedure in people, and has been performed in over 20 dogs successfully at 4 institutions in the United States. This is done with the use of fluoroscopy, cystoscopy and a diode or holmium:YAG laser. This procedure is performed on an out-patient basis at the time of cystoscopic ectopic ureter diagnosis avoiding the need for more than one anesthetic procedure for fixation. Overall, surgical fixation of ectopic ureters reports results of continued incontinence with concurrent medical intervention in anywhere from 40-71% of cases due to concurrent sphincter mechanism incompetence of the urethra (SMI).Mayhew, McLaughlin Thus far, in the author’s experience, continence has been maintained with (80%) or without (60%) concurrent medications (phenylpropanolamine) with this procedure, though more cases are needed with longer follow-up to accurately compare the procedures.
Ureteroscopy for Idiopathic Renal Hematuria
Idiopathic renal hematuria (Figure 8) is a rare condition in which a focal area of bleeding in the upper urinary tract results in long term hematuria, iron deficient anemia (chronically) and the potential for clot formation, or calculi due to blood clots, resulting in ureteral colic or signs of lower urinary tract disease. In people, the presence of a hemangioma or vascular malformations have been visualized ureteroscopically, which is cauterized through the working channel of a ureteroscope. This has also been performed in a small number of dogs to date.
ESWL for Nephro/Ureterolithiasis
Extracorporeal shock-wave lithotripsy is another minimally invasive alternative for the removal of upper tract calculi in the renal pelvis, or ureters. ESWL uses external shockwaves that is passes through a water medium directed under fluoroscopic guidance in 2 planes. The stone is shocked anywhere from 1000-2500 times at different energy levels to allow for implosion and powdering of a stone. The debris is then left to pass down the ureter into the urinary bladder over a 1-2 week period. This procedure can be performed safely in nephroliths smaller than 5 mm, and ureteroliths smaller than 3 mm. In larger stone burdens an indwelling double pigtail ureteral stent is placed prior to ESWL to aide in stone debris passage. For stones of larger sizes PCNL is recommended.
Urinary Bladder and Urethra
Laser lithotripsy is an innovative technique involving the intracorporeal fragmentation of uroliths, which is assessed using a rigid or flexible cystoscope or ureteroscope. The first report of holmium laser lithotripsy was in 1995 in human medicine (Denstdet, 1995). The holmium:YAG (yttrium, aluminum, garnet) laser is a sold-state pulsed laser that emits light at an infrared wavelength of 2100 nm. (Wollin) The energy is absorbed in less than 0.5 mm of fluid, making it safe to fragment uroliths in tight locations, as within the urethra, ureter, renal pelvis or urinary bladder, with limited risk to urothelial damage (Wollin). It combines both tissue cutting and coagulation properties, as well as the ability to fragment stones upon contact. (Wollin)
Small diameter fibers (200, 365, 550 microns) are guided through the working channel of small diameter flexible or rigid cystoscopes/ureteroscopes. Although the various commercial models of lithotriptors vary slightly, the pulse duration of the holmium laser ranges from 250-750 microseconds, the pulse energy from 0.2-4.0 J/pulse, and the frequency from 5-45 Hz, averaging a power from 3.0-100 W. The power that one chooses is based on the application one is using it for.
The laser energy is focused on the urolith surface, directed via cystoscopy. Pulsed laser energy is absorbed by water inside the urolith, resulting in a photothermal effect, which causes urolith fragmentation. The holmium laser effect on the calculus is by a vapor bubble. The vapor bubble is created when the pulse of laser energy traveling through water from the tip of the fiber is trapped within a bubble (Moses effect). If the fiber tip is 5 mm or more away from tissue, the vapor bubble collapses, the water absorbs the energy and no impact is made. As the fiber tip is advanced less than 5 mm from the calculus, the vapor bubble comes in contact with and impacts the stone. The closer the fiber tip is to the target, the larger the effect. The stone is fragmented until the pieces are small enough to be removed normograde through the urethral orifice, either via voiding urohydropropulsion or with the assistance of a stone basket. This process is useful for ureteral, cystic and urethral calculi. All stone types are able to be fragmented using laser lithotripsy.
Other urologic applications for laser lithotripsy include incision of urethral and ureteral strictures; ablation of superficial transitional cell carcinoma/prostatic adenocarcinoma within the urethral lumen, laser ablation of urinary polyps. Bladder polyps are common findings in dogs and can be associated with chronic, recurrent urinary tract infections, cystolith formation, and are often misinterpreted for cystic neoplasia. Using cystoscopy and baskets or laser lithotripsy the polyps can be removed without surgical intervention by cauterizing the stalk.
Urethral Stenting for Malignant Obstructions
Malignant obstructions of the urethra can cause severe discomfort, dysuria and life-threatening azotemia. Greater than 80% of animals with transitional cell carcinoma (TCC) of the urethra, and/or prostatic carcinoma experience dysuria and approximately 10% developing complete urinary tract obstruction. Chemotherapy and radiation therapy has been successful in slowing tumor growth but complete cure is uncommon. When signs of obstruction occur, more aggressive therapy is indicated. Placement of cystostomy tubes, transurethral resections, and surgical diversionary procedures have been described but are invasive and potentially associated with an undesirable outcome due to manual urine drainage, associated morbidity, frequent urination, and infection. Placement of self-expanding metallic stents using fluoroscopic guidance through a transurethral approach can be a fast, reliable, and safe alternative to establish urethral patency in both males and females with an 86% good to excellent palliative outcome. Urethral stenting may also be useful in patients with benign urethral strictures, or reflex dysynnergia, when traditional therapies have failed or when surgery is refused or not indicated. All animals that died after stent placement were due to reasons other than urinary obstruction, most of which being distant metastatic disease (Weisse).
A contrast cystourethrogram is performed and transurethral retrograde or antegrade guidewire access across the malignant narrowing is obtained. Measurements of the normal urethral diameter and the length of obstruction are obtained and an appropriately sized self expanding metallic urethral stent (SEMS) is chosen (approximately 10-15% greater than the normal urethral diameter and 1cm longer than the obstruction on both the cranial and caudal ends). The stent is deployed under fluoroscopic guidance and a repeat contrast cystourethrogram is performed to document restored urethral patency.
Ransurethral Submucosal Collagen Implantation
Collagen injection via urethroscopic guidance has been performed for USMI at many institutions. This procedure is indicated if medical management for SMI has failed, is contraindicated, or not tolerated. Overall success of the procedure is excellent, though the average maintenance of continence following this procedure is reported at 17 months, with re-injections being common thereafter.
Using a rigid cystoscope the urethra is cannulated and an area just caudal to the bladder trigone is identified within the urethra. A collagen heuber needle with syringe is inserted into the working channel of the cystoscope, being preloaded with the collagen material. A submucosal injection is made placing a bled into the urethral lumen. This is done in 3-4 areas, creating a new narrowing within the urethral lumen.
Antegrade Urethral Catheterization
Urethral catheterization is typically a fairly simple and routinely performed procedure in veterinary patients primarily used to monitor urine output, establish urine drainage in patients that are recumbent or have mechanical/functional urethral obstructions, or to provide urethral patency following urethral or urinary bladder surgery. Occasionally, standard retrograde catheterization can be difficult in very small (female) patients, female patients with obstructive tumors, or feline patients with urethral tears following attempts to de-obstruct blocked cats or secondary to trauma. Antegrade urethral catheterization performed under direct fluoroscopic visualization can be performed rapidly, easily, and safely in patients in whom attempts at routine retrograde catheterization have failed.
Under general anesthesia cystocentesis is performed using an 18g over-the-needle catheter, and contrast is injected to define the urinary bladder and urethra. Under fluoroscopic guidance, a guidewire is advanced antegrade into the bladder and down the urethra until exiting the penis or vulva. A urinary catheter (open-ended or pig-tail) is advanced over-the-wire in a retrograde fashion into the urinary bladder and the guidewire is removed. The urinary catheter is secured in place in a routine fashion.
Percutaneous Cystostomy Tubes
Cystostomy tubes are regularly placed during surgery to manage veterinary patients with urinary obstructions or to divert urine away from a traumatized urethra. Occasionally, these patients are severely debilitated and even a relatively short period of general anesthesia would be dangerous. A variety of cystostomy tubes and techniques are available to place these tubes quickly and safely with a percutaneous approach in order to establish urine drainage and/or diversion. Locking-loop drainage catheters have been used for such purposes in veterinary patients. These tubes can be placed via palpation alone, or with fluoroscopic or ultrasound guidance.
Many of Penn Vet's specialists are pioneering new disciplines. This is certainly true for the Jack Miller-Ebrahimi Interventional Radiology Program at Penn Vet’s Ryan Hospital. This program is the first of its kind to be established at any veterinary teaching hospital in the country, and it is named in honor of a very special puppy named Jack.
Jack was born with a liver shunt, which deprives the liver of blood supply and prevents it from developing properly. To heal Jack, the Penn Vet surgical team employed an interventional radiology technique, often used in human medicine, involving the insertion of metal coils into the shunt. The operation was a success and Jack is thriving into adulthood.
In appreciation for the life-saving care he received at Penn Vet, Jack’s owner, Ms. Mina Ebrahimi, made a generous gift to make this advanced minimally invasive treatment available to all patients in need. Today, our doctors are performing minimally invasive medical and surgical techniques for such ailments as tumors, liver shunts, urinary (urethral, bladder and ureteral) stones, bile duct obstructions, tracheal collapse, and life-threatening nose bleeds. This specialty is referred to as interventional radiology.
An established tool in human medicine, interventional radiology has tremendous potential for treatment of serious maladies in pets. Interventional radiology involves the use of contemporary imaging modalities to gain access to different structures in order to deliver materials for therapeutic reasons. The veterinary community is acquiring and refining similar procedures in human medicine to provide nonsurgical alternatives with decreased mortality rates, minimal anesthesia time, reduced hospital stay and lower costs.
Interventional radiology utilizes fluoroscopy to visualize the placement of catheters, stents, balloons and coils into blood vessels, the urinary system, the respiratory system and other tubular structures. Interventional endoscopy utilizes the endoscope under fluoroscopic guidance for diagnostic and therapeutic endeavors like malignant obstructions in the urethra, ureter, bladder, common bile duct, or intestines/colon; strictures in the urinary system, nasal passages, trachea or intestine; relieving bile duct obstructions secondary to obstructive pancreatitis, choleliths, infection or tumors; and breaking down stones in the urinary or biliary system using lithotripsy. These procedures are still largely experimental in animals and are under investigation at Penn for many different applications in companion animal patients.