Weisse

Introduction

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. Currently, the investigation and application of these techniques is expanding in veterinary medicine, particularly applications pertaining to the urinary tract. The relatively common incidence of urinary tract obstruction, neoplasia, and trauma, combined with the morbidity associated with traditional surgical techniques, makes the use of less invasive procedures such as laparoscopy, endoscopy, and interventional radiology highly appealing. This lecture will include an introduction to veterinary IR and briefly present a number of procedures including anterograde urethral catheterization, percutaneous cystostomy tube placement, palliative urethral stenting for malignant obstructions, and intra-arterial chemotherapy and arterial embolization of urogenital tumors. Total cystectomy and prostatocystotomy will also be discussed.

Techniques

Urethral Stenting for Malignant Obstructions

Malignant obstruction of the urethra can cause severe dysuria and life-threatening azotemia in some patients. Transitional cell carcinoma of the urethra and/or prostate is the most common lower urinary tract neoplasia encountered in small animal patients, with greater than 80% of dogs experiencing dysuria and approximately 10% developing complete urinary tract obstruction (Norris 1992; Knapp 2000). Chemotherapy has been successful in slowing tumor growth, but complete cures are uncommon. When signs of obstruction occur, more aggressive therapy is indicated. Cystostomy tube placement, transurethral resection, and surgical diversion have been described but are either invasive or associated with significant morbidity (complications of manual urine drainage, frequent urination, urinary tract infection) (Stiffler 2003; Liptak 2004; Fries 1991; Stone 1988). Placement of self-expanding metallic stents using fluoroscopic guidance through a transurethral approach can provide a fast, reliable, and safe alternative to establish urethral patency in both males and females. We have experienced good to excellent palliative outcomes in greater than 75% of cases (Weisse 2006). Urethral stenting may also be useful in patients with benign urethral strictures when traditional therapies have failed or when surgery is refused or not indicated.

Ureteral Stenting and Ureteral Bypass

Similar techniques are currently being employed to manage ureteral obstructions secondary to stones, strictures, or malignancies. These procedures can be performed surgically or with minimal invasiveness (percutaneously or via cystoscopy) to reduce morbidity and improve outcomes in cats and dogs. For example, dogs with ureteral obstructions can now be treated through a small needle stick through the flank or endoscopically to relieve the obstruction and be discharged on an outpatient basis. Surgically placed Subcutaneous Ureteral Bypass (SUB) devices have been placed in cats demonstrating reduced morbidity and prolonged patency rates than previously reported for feline ureteral stents. While stents are often preferred in dogs due to the minimally invasive placement options, SUBs have been used when stents failed or were not indicated (certain tumors, lack of sufficient ureteral length, etc.).

Percutaneous Bland Arterial Embolization and Chemoembolization

Bland arterial embolization entails selective, catheter-directed delivery of particulate material in order to control hemorrhage, occlude vascular malformations, or reduce tumor growth. Some current indications in human medicine include embolization of arterio-venous malformations, intractable epistaxis or gastrointestinal bleeding, and uterine artery embolization for symptomatic uterine fibroids in women. Chemoembolization involves selective intra-arterial chemotherapy delivery in conjunction with subsequent particle embolization. The authors have performed uterine artery embolization of uterine fibroids (leiyomyomata) and urinary bladder embolization for excessive tumor-associated hemorrhage. Prostatic artery embolization has also been recently successfully reported in experimental dogs as a potential technique to treat benign prostatic hyperplasia and more recently to treat prostatic cancer.