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CHAPTER 11 Interventional Oncology 175
sheaths are often placed intravascularly to allow for serial insertion the ability of veterinarians to be able to offer advanced procedures
of instrumentation into a blood vessel without concern for losing such as stenting. Although stenting procedures are now consid-
ered an important component of oncologic therapy, research is
access. Sheaths can also be created with a “peel-away” design. This
VetBooks.ir type of sheath allows for instrumentation that may have a sizeable still limited.
Most of the available literature describing stenting in compan-
external attachment piece to be introduced into a lumen or cavity.
One of the main workhorses of most IO procedures is the guide ion animals is focused on the description of the procedure and
wire. The guide wire demonstrates much of its utility as a means initial outcomes in a small cohort of animals; however, experience
of getting into a location in the least invasive way possible and in is growing, and our assessment of these procedures should expand
a relatively safe fashion. The guide wire also acts as means of place- with that growth. Stenting should be evaluated both from a pro-
ment of specialized catheters, sheaths, stents, and balloons, as these cedural and clinical outcome standpoint. In many human trials,
devices very commonly are designed with an inner cannula that the technical success of a stenting procedure is determined and
allows them to slide over a guide wire into position. Guide wires generally focuses on whether an obstruction could be bypassed
are available in a variety of lengths, diameters, shapes, and stiff- and whether a stent could be successfully placed. Clinical success
ness; these variations are particularly important to consider when is often defined as stent patency at a defined period of time after
attempting to gain access through a severely obstructed lumen. the procedure.
Specialized catheters are generally used to gain or maintain Intraluminal stent placement for the treatment of malignant
access in a luminal structure (including blood vessel) or for estab- urethral obstruction is likely the most commonly performed vet-
lishing a coaxial system, by which a smaller catheter or other erinary IO technique. Urethral stent placement is generally con-
device can also be placed. Specialized catheters are often used to sidered an attractive option for the relief of malignant obstruction,
generate contrast studies when planning ballooning and stenting as the procedure can be performed with minimal invasion and
procedures. In companion animals, the catheters used for con- often rapidly relieves obstruction. In dogs, female cats, and male
trast studies and vascular procedures are generally 4 to 5 French in cats that have had a perineal urethrostomy, urethral stents can be
diameter, although larger catheters may be used to allow for easier placed via the distal urethra without need for an incision.
drainage of an obstructed organ. In addition, much smaller cath- Several studies have described outcomes in dogs and cats
eters (microcatheters) can be used to access smaller caliber vessels undergoing urethral stenting. In four canine urethral stent studies,
during intraarterial chemotherapy delivery or embolization; as an 95 dogs undergoing stent placement to treat malignant urethral
example, the author commonly uses microcatheters that are 1.7 obstructions have been reported. 2–4 In the first study, both self-
to 2.4 French in diameter for prostatic embolization procedures. expanding and balloon-expandable stents were utilized to relieve
Stents are devices placed into a luminal structure or passage to obstruction, and stent placement was found to be rapid, safe, and
4
counteract a disease-induced stricture. The use of stents is com- effective at restoring luminal patency. Stent placement was suc-
monplace in medicine, and the disease processes treated by stent- cessful in relieving urinary obstruction in 97% of cases in the four
ing are constantly expanding. There are descriptions of stents used published studies. 2–4,11 Reported major complications of urethral
to treat malignant obstructions in the urethra, ureter, trachea, stenting have included incontinence (26%–37%), reobstruction
esophagus, colon, and blood vessels in companion animals. 2–10 In (16%), and stent migration (11%) ; in addition, stranguria
2,3
addition, stents have been used to treat malignant obstructions of poststent placement is also a common finding. Of 19 owners
2,4
the biliary tract and nasopharynx in the author’s clinic. surveyed in one study, 16 were satisfied with the outcome and
Stents can be simple catheters or other tube-like devices that are felt that they would recommend urethral stent placement to other
placed to simply allow for a lumen to be open, or specially designed owners. When treatment with nonsteroidal antiinflammatory
3
with varying metals in a variety of configurations and sizes. Stents drugs (NSAIDs) before or chemotherapy after stent placement
that contain interstices can be covered or uncovered, and can be was pursued, median survival times were significantly increased
delivered with a balloon (balloon-expandable stents) or be self- versus when medical therapy was not pursued. Urethral stent
2
expanding. If stents are covered, they can be impregnated with anti- placement has been shown to be successful in relieving malignant
neoplastic substances such as chemotherapy or radiation beads. obstructions in cats as well. 12,13
An embolic agent is a substance placed into a blood vessel to Ureteral stenting to relieve a malignant obstruction is gener-
cause temporary or permanent occlusion of blood flow. This altera- ally required when a lower urinary tract carcinoma grows from
tion of blood flow could be a partial or total occlusion of the blood the bladder, urethra, and/or prostate to obstruct the ureteral
supply depending on the eventual goal. Many different embolic orifice in the bladder. This procedure can be performed with
agents have been described, and advances in these products are con- minimal invasion using ultrasound and fluoroscopic guidance
tinuing on a regular basis. Currently, major embolic agents com- (Fig. 11.1). As the ureteral orifice is generally obscured by the
monly used during the treatment of neoplasia include particles and tumor, it is usually recommended to percutaneously gain access
liquid embolics such as cyanoacrylate or ethylene–vinyl alcohol into the renal pelvis and place a guide wire across the obstruc-
copolymer, although many other agents may be considered. tion in an antegrade fashion. Dilation of a tract through the
tumor then occurs from retrograde placement of a sheath and
dilator. The ureteral stent is also passed retrograde through the
Interventional Oncology Treatment stent and positioned with its pigtails in the renal pelvis and
Categories bladder. In one study evaluating 12 dogs undergoing ureteral
stent placement via percutaneous access, stents were successfully
5
Stenting of Malignant Strictures placed in all dogs. In dogs with azotemia before stent place-
ment, improvements in blood urea nitrogen (BUN) and serum
8
The use of stents in the treatment of companion animals has creatinine concentrations were noted in all dogs. In addition,
become commonplace over the past decade. Increased availability all dogs with follow-up ultrasonography demonstrated improved
of specialized equipment and imaging modalities has improved hydronephrosis and hydroureter. 5