Chapter 23: Interventional Radiology and Endoscopy

Question 1

Define interventional radiology:

Define interventional endoscopy:

Answer 1

Interventional radiology: Use of contemporary imaging modalities to gain access to different structures throughout the body or to deliver therapeutic materials

Interventional endoscopy: Use of endoscopes +/- fluoro to facilitate access to different structures, most commonly through natural orifices

Question 2

What should OR tables be made of to facilitate fluoroscopy?

Answer 2

Carbon fiber or plexiglas

Question 3

What form of fluoroscopy is recommended for vascular procedures?

Answer 3

Digital subtraction angiography

Takes an initial non-contrast image and then subtracts this from all further images during a run

Question 4

What type of scopes are recommended for urinary tract endoscopy in female and male dogs?

Answer 4

Female: 30 degree rigid scope ranging from 1.9-6.5mm
Male: flexible endoscope 2.5-2.8mm diameter. Can also be used to gain ureteral access

Using a rigid scope has been describe into male dogs via percutaneous perineal access

Question 5

When gaining vascular access, why is a cut down preferred for arterial vessels?

Answer 5

Permits ligation (standard) or repair (rarely) to prevent post-op hemorrhage

Question 6

After cut down, what are the two techniques for gaining vascular access?

Answer 6

1. Modified Seldinger technique: uses a simple needle (no stylet) with single wall puncture
2. Seldinger technique: An arterial needle with stylet is used, double wall puncture, stylet removed and needle is withdrawn until bevel is within lumen and blood flows

In both cases the guidewire is then placed and the needle removed

Question 7

What is the typical needle and guide wire sizes used for vascular access in larger vessels?

Answer 7

18/19g needle
0.038-0.035 inch guide wire

“In 1835-38, Seldinger modified his technique”

Question 8

What are the benefits of introduced sheaths?

Answer 8

• Allow safe, controlled, confluent dilation of the entry vessel, protection from luminal damage and hemorrhage
• Convenient side ports for flushing or administering contrast
• Check flow diaphragm to prevent back-bleeding

Question 9

What is unique about the sizing of sheaths?

Answer 9

Named for their internal diameter (a 7Fr sheath will fit over a 7Fr dilator)

Question 10

Name the following selective catheters

Answer 10

• A - marker pigtail catheter (radiopaque markers, multiple fenestrations for rapid contrast injection)
• B - Rim (reverse-curve) catheter (For accessing vessels at very acute angles)
• C - Cobra-type catheter (gentle bend facilitating access into first-order arterial branches off the aorta or vena cava)

Question 11

What are the two forms of balloon catheters used for interventional procedures?

Answer 11

• Low-pressure occlusion balloons (temporary occlusion, redirect embolisation materials, flow-directed to facilitate access)
• High-pressure balloon angioplasty catheters - filled with dilute contrast under pressure to dilate and efface strictures or stenoses

Question 12

What are the three properties by which stents are categorized?

Answer 12

• Metallic vs non-metallic
• Self-expanding vs balloon expandable
• Covered vs uncovered

Question 13

Name the following stents:

Answer 13

• A - stainless steel mesh SEMS
• B - Nitinol mesh SEMS
• C - Nitinol laser-cut SEMS
• D - Silicon-covered nitinol mesh stent graft
• E - Polyester covered mesh stent graft
• F - BEMS compressed on percutaneous transluminal angioplasty balloon
• G - BEMS after dilation

SEMS = self-expanding mesh stent, BEMS = balloon-expandable mesh stent

Question 14

What are the various properties of mesh vs woven/braided vs laser cut metallic stents?

Answer 14

• Mesh - Typically reconstrainable, have a variable degree of foreshortening
• Woven - Not reconstrainable, minor foreshortening (rarely used, no significant advantage over mesh)
• Laser cut - Shape memory nitinol (on reaching body temp, changes properties and resumes original diameter and length). Typically non-reconstrainable, minimal foreshortening. Most commonly used in urethra or vasculature but may have excessive rates of fracture within the trachea

Question 15

What are the disadvantages of covered stents?

What are their main uses in vet med?

Answer 15

Disadvantages
- increased cost
- increased material
- increased migration rates
- larger delivery systems
- can cause occlusion of adjacent structures

Uses
- Recurrent strictures or malignancies that have grown through an uncovered stent

Question 16

What are the disadvantages of balloon-expandable mesh stents?
What is their main use in vet med?

Answer 16

Disadvantages
- relatively short lengths available
- poor flexibility
- static response to compression (ie will not re-expand)

Mostly used for nasopharyngeal stenosis (short strictures surrounded by bone)

Question 17

What are the most common non-metallic stents?

Answer 17

Polyurethane compounds for use in the urinary tract such as ureteral stents - multifenestrated, double pig-tail catheters)

Question 18

List the classifications of embolics:

List some uses of embolics:

Answer 18

Embolics are compounds or devices used to obstruct blood flow.

Classifications
- Mechanical or particulate
- Temporary/biodegradable or permanent
- Solid or liquid

Uses
- Reduce hemorrhage
- Occlude vascular anomalies
- Ablate neoplasms
- Improve local concentrations of chemotherapy

Question 19

Name the following mechanical embolic devices

Answer 19

• A - Amplatz canine ductal occluder for PDA
• B - Vascular plug (side on)
• C - vascular plug (front on)
• D - Thrombogenic coils in delivery system and deployed (center) with thrombogenic Dacron fibers

Question 20

What are the most common types of liquid embolics?
How do they work?

Answer 20

• Polyvinyl alcohol particles and hydrogel microspheres
• Form initial mechanical occlusion and then permanent fibrin ingrowth

Question 21

How does n-butyl cyanacrylate glue work as a liquid embolic?
What are its reported uses?
What can be added to it to enhance its efficacy/usability?

Answer 21

• Action via vascular thrombosis and endothelial damage
• Used for vascular AV fistulas, AV malformations and thoracic duct embolisation
• Mixed with ethiodized oil (Lipiodol) to slow the rate of polymerisation and lend radiopacity
• Powdered tantalum can also be used to slow polymerisation

Passes through capillary beds increasing the risj of non-target embolisation and is more difficult to control

Question 22

What is the most common temporary embolic?
What are its reported uses?

Answer 22

• Gelatin sponge in powder, slurry or torpedo form
• Lasts days to weeks and can be sued for trauma, gastric ulcers or in a coagulopathic patient

Question 23

What are the common lasers used in interventional radiology? What are their uses?

Answer 23

• Diode laser - wavelength 980nm, absorbed well in water and hemoglobin giving good ablative and coagulation properties. Used for intramural ectopic ureters, persistent paramesonephric ducts remnants, nasal and laryngeal resections
• Ho:YAG - wavelength 2100nm, absorbed in under 0.5mm of fluid making it very useful for endourologic applications such as lithotripsy

Question 24

Describe the process of extracorporeal shockwave lithotripsy:

Answer 24

External shockwaves are passed through a water bath or waterbag and the patients soft tissue, directed under fluoro onto the stone of interest.
Shocked anywhere for 1000-3500 times at different energy levels causing implosion and powdering. Debris then moved into the bladder over 2-12 week period. Believed to be very safe and effective.

Question 25

How can you prophylactically reduce contrast-induced nephropathy?

Answer 25

• Aggressive hydration
• Anti-oxidants
• n-acetylcysteine (Renal vasodilator)