Following the description of percutaneous arterial catheterisation by Sven Ivar Seldinger in 1953, angiography developed into a widely utilised and essential medical diagnostic tool (for humans). Technological advances have since helped transform this diagnostic modality into a sub-specialisation with enormous therapeutic potential. Interventional radiology (IR) involves the use of contemporary imaging techniques such as fluoroscopy and ultrasonography to selectively access vessels and other structures in order to deliver different materials for therapeutic reasons.

Advantages and Disadvantages

The use of IR techniques in veterinary patients offers a number of advantages compared to more traditional therapies. These procedures are minimally invasive and can therefore lead to reduced perioperative morbidity and mortality, shorter anaesthesia times and shorter hospital stays. Some less equipment-intensive procedures can result in reduced costs as well. In addition, some techniques such as chemoembolisation of tumours or palliative stenting for malignant obstructions offer alternative treatment options for patients with various conditions that may not be amenable to standard therapies.

The primary disadvantages of IR include the required technical expertise, the specialised equipment necessary (fluoroscopy with or without digital subtraction capabilities) and the large 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 catheters 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 conventional or C-arm fluoroscopy can be substantial. The operator should review radiation safety guidelines, minimise exposure time and beam size, and maximise shielding and distance from the beam.

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' 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 calibre vessels and those vessels in the head (or where there is substantial bone which makes angiogram visualisation difficult).

Examples of Commonly Performed Procedures

Tracheal Stenting

Tracheal collapse is a progressive, degenerative disease of the cartilage rings in which hypocellularity and decreased glycosaminoglycan and calcium content leads to dynamic tracheal collapse during respiration. Many of these animals are palliated with medications including anti-inflammatories, cough suppressants, sedatives/tranquillisers and bronchodilators. Candidates for surgical therapy are those that have failed initial conservative medical management. Various surgical techniques have been described; however, the currently recommended surgical therapy for patients with extrathoracic tracheal collapse is extraluminal polyprolpylene ring (or spiral) prostheses. The current therapy in humans is intraluminal stenting with one of a number of FDA-approved tracheobronchial stents. A number of stents have been evaluated in the canine trachea, including both balloon-expandable (Palmaz) and self-expanding (Stainless steel, Laser-cut nitinol, Knitted nitinol) stents (Figure 1). Clinical improvement rates in 75–90% of animals treated with self-expanding, intraluminal stainless steel stents have been reported. Immediate complications were mostly minor, although there was a perioperative mortality rate of approximately 10%. Late complications included stent shortening, excessive granulation tissue, progressive tracheal collapse and stent fracture.

Figure 1. Tracheal stent.

Congenital Intrahepatic Portosystemic Shunts

Portosystemic shunts (PSSs) are anomalous vascular communications between the portal venous and systemic circulations that result in a clinical syndrome with various neurological, biochemical and haematological consequences. Numerous techniques have been described for intrahepatic PSS attenuation, ranging from careful liver dissection around the shunting vessel to more technically demanding and complicated procedures involving temporary vascular hepatic inflow occlusion for intravascular repair. A review of six major veterinary reports on canine intrahepatic PSSs reveals mortality rates following surgical treatment ranging from 10–66%. The majority of mortalities occurred perioperatively with fewer than 20% occurring later than 1 week postoperatively. The goal of IR techniques for intrahepatic PSSs is to reduce the unacceptably high perioperative mortality rates associated with traditional open surgical techniques and hopefully improve the outcome for these cases. We have performed over 60 percutaneous transvenous coil embolisations (PTCEs) with a vena caval stent and thrombogenic coils placed within the shunt. Perioperative complications were minor and perioperative mortalities were comparatively low.

Percutaneous Transarterial Embolisation and Chemoembolisation (TACE)

Bland arterial embolisation entails selective, catheter-directed delivery of particulate material in order to control haemorrhage, occlude vascular malformations or reduce tumour growth. Chemoembolisation involves selective intra-arterial chemotherapy delivery in conjunction with subsequent particle embolisation. Intra-arterial chemoembolisation has been shown to result in a 10–50-fold increase in intratumoural drug concentrations when compared to systemic intravenous chemotherapy administration. Various tumours may respond to chemoembolisation as well. We have performed this procedure in dogs with unresectable invasive sinus carcinomas with some encouraging results.

Palliative Stenting for Benign or Malignant Obstructions

Veterinary patients can present with advanced stages of malignancy in which traditional therapies such as surgery, chemotherapy or radiation therapy are associated with either excessive morbidity, cost or poor outcome. Presenting clinical signs may be associated with the tumour location and subsequent local effects rather than the systemic effects of the tumour burden. For example, malignant obstructions of the urinary tract are usually due to transitional cell carcinomas or prostatic tumours, and affected animals can present with life-threatening signs associated with urinary tract obstruction. IR techniques involving the placement of intraluminal stents to palliate similar malignant obstructions in humans have been described (Figure 2). The author has performed a number of palliative stenting procedures in the urinary tract, and upper and lower gastrointestinal tracts to relieve luminal obstructions due to neoplasia in animals as small as a ferret. These IR techniques were rapid, safe and effective, and complications were minor and uncommon.

Figure 2. Urethral stent.

Endourology

Similar techniques are currently being employed to manage ureteral obstructions secondary to stones (Figure 3), strictures or malignancies. These procedures can be performed surgically or with minimal invasiveness (percutaneously or via cystoscopy) to reduce morbidity and improve outcomes in certain patients.

Figure 3. Ureteral stent.

References

References are available upon request.