Interventional radiology involves the use of imaging modalities such as fluoroscopy or ultrasonography to gain access to different
structures in order to deliver materials for therapeutic purposes. The use of interventional 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 anesthesia times and shorter hospital stays. Some techniques
such as chemoembolization of tumors or palliative stenting for malignant obstructions offer alternative treatment options
for patients with conditions that may not be amenable to standard therapies. There are not necessarily disadvantages for
the patient as much as the provider, in the initial cost of equipment and time to gain expertise. Radiation exposure to personnel
can be substantial when using fluoroscopic guidance and full lead gowns, thyroid shields, and leaded glasses are recommended
and may add to the initial purchase price of equipment.
Small and toy breed dogs are predisposed to tracheal collapse due to cartilage degeneration. The trachea collapses dynamically
during respiration. These patients can present with mild "honking" to respiratory distress due to complete airway obstruction.
Aggressive medical management is the treatment of choice in these patients. Combinations of anti-inflammatories, cough suppressants,
sedatives, bronchodilators, antibiotics, weight loss, restricted exercise, and removal of inhaled allergens (such as smoke)
can help to control clinical signs. Treatment of concomitant diseases is imperative as well. Small airway disease, pulmonary
parenchymal disease, heart disease, and brachycephalic airway syndrome exacerbate tracheal collapse and should be addressed.
Patients that fail this aggressive management and concurrent diseases have been adequated treated can be candidates for interventional
or surgical treatments. Extraluminal tracheal ring prostheses has a reported efficacy of 75-85% for extrathoracic tracheal
collapse, but significant morbidity is associated with surgery. Complications such as laryngeal paralysis, perioperative
death, and permanent tracheotomy can be seen. If significant intrathoracic tracheal collapse is present surgery can have even
higher morbidity. Intraluminal self-expanding metallic nitinol stents have excellent flexibility and can now be placed in
the trachea (both cervical and intrathoracic) to treat tracheal collapse using a minimally invasive procedure. Another advantage
of tracheal stent placement versus surgery is the short anesthesia time, which is beneficial in geriatric patients with concurrent
cardiac or pulmonary disease. It is important to realize that medications will still be required in a majority of patients
following stent placement however. When used appropriately with careful patient selection, significant improvement in the
quality of life can be achieved with stent placement in addition to medical management, with a lower morbidity than surgery.
There have however been complications associated with intraluminal tracheal stent placement which include stent shortening,
excessive granulation tissue, progressive tracheal collapse and stent fracture. In young patients, stents should be carefully
considered as the life span of these stents has not been determined.
Nasopharyngeal stenosis is a condition which there is narrowing of the nasopharynx caudal to choane resulting in stertorous
breathing with an exaggerated inspiratory effort. These patients often have severe mucoid to mucopurulent nasal discharge
for long periods of time (weeks to years). This can be congenital or acquired in etiology and is more common in cats than
dogs. Balloon dilation has been used successfully as has numerous surgical procedures. Balloon dilation may allow for recurrent
stenosis to occur. Surgery can require a long anesthetic procedure and is invasive. A reported alternative treatment is
balloon expandable metallic nasopharyngeal stent placement. It was rapidly performed in an average of 38 minutes, and was
effective in relieving clinical signs for 12-28 months.
Transitional cell carcinoma is a common neoplasia of the urinary bladder and urethra of dogs. Local disease results in approximately
10% of TCC cases developing complete urinary tract obstruction due to tumor progression. The cause of death is due to the
primary tumor in up to 60% of cases. Clinical signs are most often associated with the primary tumor and include both dysuria
and complete urinary tract obstruction. Prostatic neoplasia (most commonly adenocarcinoma) is another common tumor that affects
the urinary tract in male dogs. Clinical signs in this disease are associated with the local affects of the tumor in up to
40% of these dogs. Minimally invasive techniques to palliate the clinical signs associated with local disease include ultrasound
guided laser ablation and balloon expandable and self expanding metallic urethral stents. Stents can be placed under fluoroscopic
guidance rapidly, safely, and effectively relieve urethral obstructions. In a small study involving urethral stent placent
in 12 patients, seven dogs had good to excellent outcome, 3 had fair outcome and 2 had a poor outcome (severe incontinence
and atonic bladder). Palliative stenting can also be useful in malignant obstructions in the gastrointestinal tract (due to
leiomyosarcoma or adenocarcinoma) to relieve constipation/ obstipation dyschezia and/or tenesmus.
Ureteral stents can also be placed for both benign (stricture or stone) obstructions as well as malignant obstructions (TCC
occluding the ureterovesicular junction). The use of interventional and minimally invasive radiology techniques in the ureters
are increasingly being studied and continue to evolve.