Following the trends in human medicine, there is an ongoing effort to adapt and develop minimally invasive therapeutics for the management of various problems facing veterinary patients. Minimally invasive therapeutics offer the advantages of smaller incisions, decreased pain, shortened anesthesia times, and shorter length-of-stay compared to traditional open surgical approaches. Currently in veterinary medicine, laparoscopy, thoracoscopy, minimally invasive orthopedic procedures, endourology, and interventional radiology are meeting this demand.
Interventional radiology (IR) involves the use of contemporary imaging modalities, such as fluoroscopy, endoscopy, ultrasound, CT, and MRI (or combinations thereof), to gain access to different structures in order to deliver materials for therapeutic purposes. IR is a subspecialty of radiology in human medicine. IR techniques have been widely utilized in human medicine for the past 20-30 years to effect minimally invasive diagnostic and therapeutic outcomes. Applications of IR in veterinary medicine are just being realized. The purpose of these proceedings is to present current applications of IR in veterinary medicine.
Equipment and Training
Many IR procedures require advanced imaging modalities. Fluoroscopy is a critical tool for performing most IR procedures. In IR, an array of guide wires with various properties, catheters specifically adapted for individual procedures and anatomy, stents composed of different materials and configurations, embolic coils, embolic particles, drainage devices, surgical glue, oils, chemotherapeutic agents, occlusion devices, balloons, etc. replace the standard surgical pack.
Because IR is so new to veterinary medicine, there are only two formal training programs in veterinary interventional radiology. They are at Michigan State University and the Veterinary Hospital of the University of Pennsylvania. It should be noted that many of the already developed veterinary IR procedures could result in significant harm or even death if improperly performed.
IR Applications in Veterinary Medicine
Potential applications of IR techniques for the management of veterinary disease states are boundless. The following paragraphs describe four common IR procedures involving the respiratory, hepatic, urogenital, and gastrointestinal systems. The table at the end of the proceedings describes other common IR applications being performed in veterinary medicine.
Tracheal collapse is a common affliction of small breed dogs. Traditional management of tracheal collapse is centered on medical management (cough suppressants, corticosteroids, management of concurrent problems). Surgical management using prosthetic rings placed around the trachea is an option in patients with cervical tracheal collapse that fail medical management. Surgical management of tracheal collapse tends to be invasive and is associated with a significant incidence of complications including but not limited to disruption of the tracheal blood supply, injury to the recurrent laryngeal nerve causing laryngeal paralysis, and the inability to access the intrathoracic trachea.
Tracheal stenting involves the placement of an intraluminal self-expanding metallic stent that holds the trachea open. Placement requires the use of fluoroscopy. Tracheal stenting offers a very rapid, non-surgical (everything is done through the airway) treatment option for animals with tracheal collapse. The incidence of acute complications is very low when compared to prosthetic ring placement provided the stent is sized and deployed appropriately. Long-term complications may include inflammatory tissue formation at the ends of the tracheal stent. This problem tends to be very steroid responsive and resolves rapidly. Stent fracture is another complication and occurs primarily in animals that continue to cough severely. As a result, ongoing medical management is still important although most patients require a less rigorous medication protocol.
Currently, the author recommends tracheal stent placement for dogs with tracheal collapse that are not having good quality of life in the face of medical management, those with intrathoracic tracheal collapse, and those whose owner does not wish to pursue a surgical treatment option. Dogs with intrathoracic tracheal collapse and mainstem bronchial collapse often benefit significantly from tracheal stent placement although they often continue to cough due to the mainstem bronchial collapse. Cervical tracheal collapse may be treated through traditional surgical techniques or placement of a tracheal stent. The entire procedure takes approximately 30 minutes and usually requires only 24 hours total hospitalization. It is important for clients to recognize that tracheal collapse is a progressive condition. This being said, tracheal stent placement offers an excellent palliative treatment option.
Malignant urethral obstruction: Transitional cell carcinoma, prostatic carcinoma, and other intrapelvic neoplasia may result in urethral obstruction. Traditional therapy has been centered on diverting urine via surgical placement of a cystostomy tube while pursuing traditional tumor-directed therapies. Cystostomy tube placement requires surgery and requires significant owner maintenance for the duration of the pet’s life. In addition, complications including tube dislodgement and recurrent, frequently multi-drug resistant urinary tract infection are not uncommon. Using IR techniques, an intraluminal self-expanding metallic urethral stent can be placed (non-surgically) via the vulva or penis to open the urethral lumen. Note that stents for this purpose are very different than those used for other applications. Using fluoroscopy, the length and width of the obstruction can be very precisely measured and a stent of an appropriate length and width to span the obstruction chosen. The stent is deployed from a delivery system introduced via the urethral orifice. The entire procedure takes approximately 1hour and is associated with little to no patient discomfort. Most often, patients are able to urinate immediately after stent placement. The greatest complication of the procedure is incontinence. Incontinence results from the stent spanning the urethral sphincter and at times, a significant portion of the urethra. The overall incidence of incontinence after stent placement is <20%. Females logically have greater problems with this than males. In a case series by Weisse et al. and based on the MSU experience, no patients died in the short or long term due to recurrent urethral obstruction.1 With the symptom of the neoplastic condition palliated, chemotherapy, radiation therapy or other adjunctive treatments may be utilized to address the underlying neoplasia.
Intrahepatic portosystemic shunt: The literature clearly illustrates that dogs with intrahepatic portosystemic shunt (IHPSS) have a very high incidence of surgical morbidity and mortality (10-50%). A technique for the repair of these shunts via an endovascular approach has been perfected at the University of Pennsylvania and is being performed regularly at Michigan State University and 1-2 other centers around the country. The technique is called a Percutaneous Transjugular Coil Embolization procedure. In short, the exact anatomy of the shunt is identified using Helical CT Portography (CT Angiography). Once the anatomy of the shunt is identified, the repair is performed under fluoroscopic guidance. Under general anesthesia, a large sheath introducer is placed in the jugular vein for the introduction of catheters, wires and stent. The shunt is localized in relation to the caudal vena cava angiographically. An appropriately sized caval stent is placed in the caudal vena cava at the mouth of the shunt. Through the stent, embolic coils are placed to partially attenuate the shunt while concurrently monitoring portal pressures (through the same catheter). The resulting increase in portal pressure results in increased hepatic portal flow, subsequent liver growth and development, and thus patient growth and development. The patient recovers from anesthesia and is discharged the following day. Procedural time is approximately 1.5 hrs and there is only a 4mm incision over the jugular vein. Acute morbidity and mortality are extremely rare. Approximately 30% of dogs undergoing this procedure require additional coils to be placed 3-12 months later to further attenuate the shunt and further increase hepatic flow.
Nasojejunal tube placement: Enteral nutritional support is associated with decreased length of stay, fewer infective complications, and significant cost savings when compared to parenteral nutritional support in people with critical illness. Nasogastric and nasoesophgeal tube placement is quick and the procedure is generally well-tolerated in small animal patients. However, many of these patients demonstrate nausea or vomiting associated with feeding into the stomach. Feeding distal to the stomach allows for the provision of enteral nutritional support in this patient population. Traditional surgical jejunostomy is invasive (requires surgery or laparoscopy) and is associated with significant complications including ostomy complications and septic peritonitis. A technique has been described for fluoroscopically-guided nasojejunal tube placement by Wohl et al, however, the technique was associated with a significant incidence of failure to achieve transpyloric passage and failure to achieve jejunal access. Tubes that only reached into the duodenum were frequently associated with oral migration. We describe a technique also utilizing fluoroscopy in which a combination of berenstein catheter and 260cm hydrophilic guidewire are utilized to gain guidewire access to the jejunum. Finally, the catheter is removed and a feeding tube is placed over the guidewire and sutured adjacent to the nasal planum. In our experience, ability to achieve transpyloric access is 100%. Ability to gain jejunal access is 84%. Oral migration is very rare. This technique has become standard of care in our service in patients with pancreatitis, septic peritonitis, and conditions associated with protracted vomiting or gastric motility disorders.
Additional Veterinary IR Procedures
- Transarterial Chemoembolization (TACE): For non-resectable hepatic neoplasia.
- Transarterial Chemotherapy or Embolization: For palliative treatment of unresectable neoplastic disease. Example: Embolization for pain control for metastatic bone disease. Potential delivery of chemotherapy as a radiation sensitizer.
- Stenting of malignant urethral or ureteral obstruction
- Stenting of malignant vascular obstruction
- Stenting of malignant airway obstruction when surgery is contraindicated or not desired.
Stenting of malignant gastrointestinal obstruction when surgery is contraindicated or not desired.
- Nasojejunal feeding tube placement using IR techniques.
- Percutaneous gastrostomy tube placement
- Percutaneous gastrojejunostomy tube placement
- Esophagojejunostomy tube placement
- Urinary applications
- Percutaneous nephrostomy tube placement
- Ureteral stent placement for urolithiasis
- Ureteral stent placement for malignant ureteral obstruction (bladder neck)
- Urethral disruption (iatrogenic or traumatic): Antegrade wire access with retrograde locking loop catheter placement into bladder. Indicated when retrograde catheterization fails. Frequently obviates the need for surgical intervention as the urethra heals over the catheter.
- Vascular foreign body retrieval
- Tracheobronchial foreign body retrieval
- Glue embolization of hepatic arteriovenous malformations
- Glue embolization of thoracic duct
- Biliary drainages
- Esophageal stricture stenting (in concert with balloon dilation to decrease necessity for repeated dilations).
- Nasal embolization for intractable epistaxis. Unlike carotid artery ligation, this procedure may be repeated as needed.
- Repair of complex vascular malformations
- Balloon pericardiotomy for recurrent pericardial effusion
- Pericardial drain placement for pericardial effusion decompression
- Miscellaneous drainages
- In-dwelling drainage catheters with subcutaneous access port
- Diagnostic peripheral angiography