Download Interventional Radiology and the referral patient

Interventional Radiology and the referral patient - stents, biopsies, advanced imaging
Lisa G. Britt, DVM, MS,
Diplomate American College of Veterinary Radiology,
Clinical Assistant Professor @ University of Missouri’s
College of Veterinary Medicine
Interventional radiology (IR) refers to the use of advanced imaging techniques including ultrasound,
fluoroscopy, CT, endoscopy, and MRI to obtain biopsies for diagnostic information or to deliver various
agents or devices for treatment of disease. In some cases, interventional radiology techniques offer the
only realistic approach to treating an animal when they minimize costs and/or potential stricture.
Advantages and Disadvantages
The use of IR techniques in veterinary patients offers a number of advantages to more traditional
therapies. These procedures are minimally invasive and can therefore lead to reduced peri-operative
morbidity and mortality, shorter anesthesia times, decreased pain, shorter hospital stays, and often a
more rapid return towards good health. Some less equipment-intensive procedures can result in
reduced costs as well. In addition, some techniques such as chemoembolization of tumors or palliative
stenting for malignant obstructions offer treatment options for patients with various conditions that
may not be amenable to standard therapies or when the standard-of-care treatments are associated
with excessive morbidity, cost, or poor outcome.
The primary disadvantages of IR include the required technical expertise that is not part of traditional
veterinary training, the specialized equipment necessary (fluoroscopy with or without digital subtraction
capabilities), and the initial capital investment necessary to provide a suitable inventory of catheters,
guide wires, balloons, stents and coils. Radiation exposure to personnel can be substantial when using
fluoroscopic guidance and full lead gowns, thyroid shields, and leaded glasses are recommended.
Some of the more common disorders treated with interventional radiology procedures include:
1. Tracheal collapse correction with intraluminal stents:
Older toy and small breed dogs that present with “goose honking” coughs often suffer from
some degree of tracheal collapse. If caught early, medical management such as coughsuppressants, bronchodilators, anti-inflammatories, weight loss, exercise restriction and/or
removal of allergens such as smoke is initiated for these patients to help control clinical signs.
When these therapies fail, or if an animal presents in such severe respiratory distress that it
does not have time to respond to even the most aggressive medical management, immediate
recovery of a normal tracheal luminal diameter is the only option. While extra-tracheal ring
prostheses are very successful with an efficacy of 75-85% for extrathoracic tracheal collapse, the
significant surgical complications such as laryngeal paralysis, the need of a permanent
tracheotomy, or perioperative death can be seen. Even higher surgical morbidity can be seen
when intrathoracic tracheal collapse is present. Using fluoroscopy, IR assisted intraluminal selfexpanding metallic nitinol stents can be placed in the cervical and/or intrathoracic trachea. This
is a minimally invasive procedure, the stents have excellent flexibility, and they can be
overlapped when the length of collapsing trachea exceeds the length of available stents with a
given diameter. At the University of Missouri, we have admitted some patients that received
intraluminal stents using IR as an emergency procedure necessary to save them and a few
others whose tracheas collapsed after surgery for something unrelated and could not be
weaned off the ventilator until a stent was placed. Any other underlying or contributing disease
such as small airway disease, heart disease, obesity, and treatable components of
brachycephalic airway syndrome should be addressed concurrently or optimally prior to
tracheal stent placement whenever possible. Complications associated with intraluminal
tracheal stent placement include stent shortening or fracture, excessive granulation tissue,
progressive tracheal collapse. Medications usually remain necessary and many dogs retain a
mild cough.
2. Diagnostic and therapeutic angiography:
a. Balloon valvuloplasty for pulmonic stenosis
b. Canine ductal occlusion for patent ductus arteriosus (PDA)
Embolization coils can be placed through an intravenous catheter into the PDA or an
Amplatz canine ductal occluder can be inserted.
c. Temporary and Permanent Pacemakers for Bradyarrhythmias
d. Stenting and Coil Embolization for Hepatic Shunts (Intravascular)
Portosystemic shunts (PSS) are abnormal vascular communications between the portal
venous system and the systemic circulation and can be diagnosed non-invasively using
ultrasound and portal scintigraphy (transcolonic or splenic). Ultrasound is 81% sensitive
but only 67% specific. Nuclear scintigraphy has greater sensitivity and specificity in
detecting portosystemic shunts, but does not allow differentiation between intrahepatic
and extrahepatic shunts. Definitive identification and anatomic characterization of the
PSS can be achieved minimally invasively with interventional diagnostic angiographic
procedures, such as transvenous retrograde portography. This type of portography is a
minimally invasive interventional diagnostic procedure that can provide definitive
anatomic localization of the PSS and does not require a celiotomy like mesenteric
portography does. Most congenital portosystemic shunts are extrahepatic in origin and
the surgical occlusion success rate is high. Intrahepatic portosystemic shunts are less
common, are surgically challenging for veterinary surgeons to treat, and have a high
morbidity and mortality rate. A balloon jugular catheter is passed into the caudal vena
cava and pressure measurements can be performed. Next, the cava is occluded and nonionic iodinated contrast is administered resulting in retrograde filling of the abdominal
vena cava and any PSS. After localizing the shunt, thrombogenic coils can be used for
staged embolization with or without stent placement. Complications can include coil
migration into the heart and lungs.
e. Embolization of arterio-venous malformations
f. Transarterial embolization of hepatic or renal tumors
g. Directed treatment material deposition of various tumors (radioactive isotopes,
chemoembolization)
Percutaneous arterial embolization with and without chemoembolization techniques can
be performed. Arterial embolization allows particulate material to be delivered directly
to a location by use of a selective catheter in order to occlude vascular malformations
(most commonly shunts), control hemorrhage, or reduce malformations. With
chemoembolization, chemotherapy is delivered directly to the tumor which can result in
a 10-50 times higher intra-tumoral drug concentration than systemic chemotherapy with
less systemic toxicity. This may be of special benefit in non-resectable hepatocellular
carcinomas.
3. Urinary tract stenting
a. Urethral stenting (retrograde or antegrade)
i. Bypass bladder, intra-urethral, and/or prostate tumors
ii. Canine incontinence
Transitional cell carcinoma (TCC) is a common neoplasia of the urinary bladder and
urethra of dogs. Urinary tract obstruction occurs in approximately 10% of TCC cases
due to the location and severity of local tumor progression. This local disease leads
to death in up to 60% of cases. Hydronephrosis is a common sequelae to the
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 effects of the tumor in up to 40% of these dogs and include stranguria
as well as tenesmus. Hydronephrosis can also occur when these tumors grow
cranially up the prostatic urethra into the bladder trigone. Minimally invasive
techniques to palliate the clinical signs associated with local disease include
ultrasound guided laser ablation, as well as balloon expandable and self expanding
metallic urethral stents placed with fluoroscopic guidance. In addition, interventional
radiology can be used for treatment of prostatic tumors like those enrolled in a
current MU CVM study using radioactive gold nanoparticles placed into prostatic
tumors using CT guidance.
b. Ureteral stenting
Ureteral stents can also be placed for both benign obstructions such as those caused
by a ureteral stricture or calculus, as well as malignant obstructions e.g., TCC
occluding the ureterovesicular junction.
4. Nasopharyngeal Stenosis:
Animals that suffer from nasopharyngeal stenosis have narrowing of the nasopharynx caudal to
the choanae. This narrowing results in stertorous breathing with an exaggerated inspiratory
effort. Patients often present with a complaint of severe mucoid to mucopurulent nasal
discharge that has lasted for long periods of time (sometimes years). Nasopharyngeal stenosis is
more common in cats than dogs, and can be congenital or acquired in etiology. Balloon dilation
has been used successfully as have numerous surgical procedures but recurrent stenosis can
occur with balloon dilation and surgery is invasive and can require a long anesthetic procedure.
An alternative treatment is the placement of a balloon expandable metallic nasopharyngeal
stent. It can be performed rapidly and was reported to be effective in relieving clinical signs for
12-28 months.
5.
Parathyroid tumors – Ultrasound guidance is used to guide a needle into the parathyroid
gland/tumor to inject ethanol into the tumor for chemical ablation.
References
1. Berent AC, Weisse C, Todd K, et al. Use of balloon-expandable metallic stent for treatment of
nasopharyngeal stenosis in dogs and cats: six cases (2005-2007). J Am Vet Med Assoc 233(9): 1432-1440,
2008
2. Bostwick DR, Twedt DC. Intrahepatic and extrahepatic portal venous anomalies in dogs: 52 cases
(1982-1992). J Am Vet Med Assoc 206(8): 1181-185, 1995.
3. Mann FA, Barrett RJ, Henderson RA. Use of a retained urethral catheter in three dogs with prostatic
neoplasia. Vet Surg 21:342-47, 1992
4. Miller MW, Fossum TW, Bahr AM. Transvenous retrograde portography for identifaction and
characterization of portosystemic shunts in dogs. J Am Vet Med Assoc 221(11): 1586-1590, 2002
5. Mittleman E, Weisse C, Mehler SJ. Fracture of an endoluminal nitinol stent used in the treatment of
tracheal collapse in a dog. J Am Vet Med Assoc 225(8): 1217-1221, 2004
6. Moritz A, Schneider M, Bauer N. Management of advanced tracheal collapse in dogs using
intraluminal self-expanding biliary wall stents. J Vet Inter Med 2004: 18: 31-42
7. Newman RG, Mehler SJ, Kitchell BE, et al. Use of a balloon-expandable metallic stent to relieve
malignant urethral obstruction in a cat. J Am Vet Med Assoc 234(2): 236-239, 2009.
8. Norris JL, Boulay JP, Beck KA, et. Intralumina self-expanding stent placement for the treatment of
tracheal collapse in dogs (abstr), in Proceedings, 10th Annual Meeting of the American College of
Veterinary Surgeons, 2000.
9. Sun F, Uson J, Crisostomo V. Interventional cardiovascular techniques in small animal practice. J Am
Vet Med Assoc 227(3): 394-408, 2005.
10. Weisse C. Advances in Small Animal Medicine and Surgery. November 2007
11. Weisse C, Berent AC, Todd K, et al. Evaluation of palliative stenting for management of malignant
urethral obstructions in dogs. J Am Vet Med Assoc 229(2): 226-34, 2006
12. Weisse C, Hume DZ, Berent A, et al. Palliative stenting for malignant obstructions in a dog, cat and
ferret (abstr), in Proceedings, 14th Annual Meeting of the American College of Veterinary Surgeons,
2004.
13. Weisse C, Schwartz K, Stronger R, et al. Transjugular coil embolization of an intrahepatic
portosystemic shunt in a cat. J Am Vet Med Assoc 221(9): 1287-91, 2002
14. Weisse C, Solomon JA, Holt D, et al. Percutaneous transvenous coil embolization of canine
intrahepatic portosystemic shunts: Short term results in 14 dogs (abstr), in Proceedings, 13th Annual
Meeting of the American College of Veterinary Surgeons, 2003.
Some of the Veterinary facilities currently offering Interventional Radiology:
Cornell University Veterinary Specialists
UC Davis, CA - William R. Pritchard Veterinary Medical Teaching Hospital
University of Georgia College of Veterinary Medicine
Michigan State University Veterinary Teaching Hospital
Mississippi State University’s College of Veterinary Medicine
*University of Missouri Veterinary Teaching Hospital
North Carolina State University Randall B. Terry, Jr Companion Animal Veterinary Medical Center
The Ohio State University Veterinary Medical Center
Oregon State University – Lois Bates Acheson Veterinary Hospital
University of Pennsylvania’s Ryan Veterinary Hospital
*Purdue University College of Veterinary Medicine (cardiology procedures)
Texas A&M University’s Veterinary Hospital
Tufts University – Cummings School of Veterinary Medicine
University of Wisconsin-Madison Veterinary Medical Teaching Hospital
Washington State University Veterinary Medical Hospital
The Animal Medical Center in New York *Chick Weisse VMD, DACVS
VetMed referral hospital in Arizona
Veterinary Specialty Center(s) – (Buffalo Grove, Chicago, and Crystal Lake IL; Mount Pleasant WI)
VCA Northwest Veterinary Specialists
NorthStar VETS Robbinsville, NJ