Interventional radiology (IR) is a subspecialty of radiology in which minimally invasive procedures are performed usually using fluoroscopic image-guidance.
The fluoroscopic images taken during procedures provide road maps that allow the clinician to guide instruments such as catheters and guide wires through the body to the areas of interest. This is one of the fastest growing fields in human medicine, and IR procedures are now routinely performed for a wide variety of indications such as angioplasty, aneurysmal patching, management of cerebral haemorrhage, and palliative malignancy stenting.
Endoscopy is now routinely performed in veterinary patients and allows minimally invasive examination and biopsy of areas such as the bowel and nose with either a rigid or flexible camera. Interventional Endoscopy (IE) utilises advanced endoscopic techniques to provide minimally invasive therapeutic procedures as an alternative to surgery or in patients in which surgery may not be appropriate.
There is an increasing understanding that a number of the techniques used in human patients can be adapted for dog and cats that have previously had limited or no therapeutic options (see below). Many of the adapted interventional techniques used in dogs and cats require the use of both endoscopy and fluoroscopy simultaneously.
Ian Battersby (Internal Medicine clinician) and Ronan Doyle (Soft Tissue surgeon) have developed and run the Interventional Radiology and Interventional Endoscopy Service at Davies Veterinary Specialists. They are very happy to discuss patients that may benefit from these techniques.
Some examples of Interventional Radiology and Interventional Endoscopy procedures used in dogs and cats include:
Extravascular procedures:
Ureteral stents
These can be placed in a retrograde manner in patients with ureteral obstructions, such as with ureterolithiasis (a stone within the ureter). If the patient is large enough the stents can be placed without surgery using a combination of cystoscopy and fluoroscopy to by pass the obstruction.
Figure 1
An intraoperative fluoroscopy image taken during the placement of two double pigtail ureteral stents in a cat with bilateral ureteral obstruction caused by stones.
Nephrostomy tubes in acute obstruction of ureter by ureteroliths
If a ureteral obstruction occurs acutely the patient may not be metabolically stable to allow a prolonged procedure. In this situation a nephrostomy tube can be placed as a temporary measure. This prevents worsening of a patient’s renal function and allows stabilization, so that ureteral stenting can be planned and performed as an elective procedure.
Urethral stents
These can be placed for the alleviation of dysuria and stranguria (difficulty passing urine) in dogs with bladder neck or prostatic tumours.
Figure 2
A radiograph of a Cocker Spaniel following placement of a self expanding metal stent in the urethra. To relieve urinary obstruction caused by a bladder tumour (transitional cell carcinoma).
Ectopic ureters
A congential problem resulting in incontinence primarily in the young dog but occasionally diagnosed in the older dog. Traditionally surgery is required, however using a combination of cystoscopy and fluoroscopy, the ectopic ureters can be repositioned to open into the bladder.
Urethral bulking injection for urinary incontinence
When medical management of incontinence has failed bulking injections are an alternative to traditional surgeries. Injections of a bulking material are made into the urethra (outflow of the bladder).
Nasopharyngeal Stents
These can be placed in patients with benign or malignant nasopharyngeal strictures that are refractory to conventional treatments.
Tracheal stents for the treatment of tracheal collapse
Our experience is that the majority of tracheal collapse patients respond well to targeted medical therapy after an appropriate diagnostic evaluation, however a small proportion do not. For these patients further treatment with the placement of an intraluminal self-expanding stent or possibly surgery may be beneficial.
Figure 3
A radiograph of a Yorkshire Terrier with tracheal collapse. Following placement of a self expanding metal stent.
Balloon dilation and Stenting of Oesophageal strictures
In humans self-expanding stents are used in both benign and malignant oesophageal and colonic strictures. This technique can be used in patient’s refractory to balloon dilation or early in the treatment phase to prevent repeated dilations and general anesthetics.
Figure 4
An endoscopic view of the oesphagus following placement of biodegradable stent for the management of an oesphageal stricture in a cat.
Intravascular procedures:
Intravascular interventional procedures (also know as pin hole surgery) have also been adapted from human to veterinary patients. These techniques use a series of wires and catheters introduced via a blood vessel to access areas that are difficult to reach surgically. Using the catheters drugs can be delivered to specific areas (for example chemotherapy) or agents or vascular stents can be placed to occlude or improve blood flow.
Some of the procedures that can be performed in dogs and cats include:
Chemoembolisation in non-resectable liver tumours
This involves localised delivery of drugs directly to a tumour via its blood supply. The blood supply to the tumour is then subsequently blocked.
Embolisation in refractory epistaxis
In patients with uncontrollable nose bleeds, wires can be guided via blood vessels into the small vessels of the nose. Following this, embolic agents can then be used to stop the blood leaking from the bleeding vessel.
Vascular Occlusion
In patients in which a blood vessel is compressed or occluded by tumours or blood clots, an intravascular self-expanding stents can be placed to improve blood flow.
Occlusion of Congential Portosytemic Shunts not amenable to surgery
Dr Carolyn Burton of the soft tissue surgical service at DVS has unsurpassed experience in the surgical management of patients with portosystemic shunts, with an outstanding success rate and minimal complications. The most challenging shunts are in patients that have shunting vessels within the liver (called intrahepatic shunts). Dr Burton is able to surgically manage these patients with good results, but in a small number of cases surgery is not technically possible. In this select group of patients, intravascular radiology techniques can be used to deliver stents and coils into the vessel to occlude the blood flow through the shunting vessel.