Interventional radiology in veterinary care
Minimally invasive procedures can have maximum benefits, experts say
Jun 01, 2008
East Lansing, Mich. — The introduction of minimally invasive procedures such as interventional radiology offers the same benefits to animals that similar procedures have made possible in human medicine, according to one practitioner.
"As people experience less invasive procedures for their own health care and that of their family members, it evolved that their pets should experience the same advantages," says Matthew W. Beal, DVM, Dipl. ACVECC (American College of Veterinary Emergency and Critical Care).
Beal is director of Emergency and Critical Care Medicine and director of Interventional Radiology Services at Michigan State University's College of Veterinary Medicine at East Lansing.Interventional radiology (IR) uses contemporary imaging techniques such as fluoroscopy, endoscopy, ultrasound, computed tomography (CT) and magnetic resonance imaging (MRI) to access different areas and structures of the body for therapeutic treatment.
In these approaches, standard surgical instruments are replaced by a wide variety of specially adapted devices, including guide wires, catheters, stents, balloons, coils and occlusion devices.
As a subspecialty of radiology, IR has been a part of human medical care for more than 20 years, but this approach has been applied only recently to veterinary patients.
According to Beal, the IR approach can be adapted to many situations and can offer the benefits of surgical intervention to patients for whom surgery may not necessarily be a good option. Among the procedures available, three of the most common involve treatments for tracheal collapse, portosystemic shunt and management of nutritional support.
Tracheal collapse is a condition primarily of middle-aged small and toy-breed dogs where progressive degeneration of the cartilage rings leads to flattening and collapse of the trachea. When medical management of cough, gagging and respiratory symptoms has been unsuccessful, surgery to place supporting prosthetic rings around the trachea has been the traditional treatment of choice.
However, this procedure can result in complications, such as disruption of the tracheal blood supply, as well as laryngeal nerve damage and subsequent laryngeal paralysis. In addition, prosthetic ring placement generally is carried out only when the collapse is in the cervical region.
An IR alternative to open surgery involves placement of an intraluminal stent into the collapsed area of the trachea. Under fluoroscopic guidance, the stent is placed via an endotracheal tube and deployed into the trachea. The outward radial force of the stent holds the trachea in a more open position.
Intraluminal stent placement also offers an effective treatment option to those dogs suffering from intrathoracic collapse where external tracheal support rings cannot be used. In most cases, the stenting procedure usually takes less than an hour to perform, is essentially pain-free and requires only 24 hours of post-operative hospital care.
Intrahepatic portosystemic shunt
With portosystemic shunts, an abnormal communication exists between the portal vein and the systemic circulation (usually the vena cava) which bypasses the liver, resulting in severe liver dysfunction. When the shunt exists outside the liver, as is the usual case with smaller breeds of dog, surgical repair can be an excellent option. But in larger breeds, the shunt is usually intrahepatic. Surgical repair of these cases is not only very difficult but carries a mortality rate of 7 percent to 70 percent.
Using an IR technique popularized at the University of Pennsylvania by Chick Weisse, VMD, Dipl. ACVS, repair of the shunt can be performed intravascularly through intravenous access in the jugular vein. This technique, called percutaneous transjugular coil embolization, is performed under fluoroscopic guidance.
After details of the shunt anatomy are identified using helical CT portography, the shunt is partially occluded using embolic coils. A stent placed in the vena cava prevents migration of the coil into the systemic circulation. By creating a favorable pressure gradient between the shunt and the vena cava, hepatic blood flow via the portal vein should increase. The increased blood flow stimulates liver growth, decreasing related symptoms for the patient.
This procedure takes approximately 90 minutes to perform but, more importantly, the morbidity and mortality rates are very low.
"Many surgeons were reluctant to perform open surgical repair of intrahepatic portosystemic shunts due to the high morbidity and mortality rates. But the veterinary community has recognized that this new procedure is valuable," Beal says. "It used to be that two or three of these procedures were performed in a year, but we have four scheduled in the coming month."