Page 195 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

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Interventional Oncology

WILLIAM T.N. CULP

1
The field of interventional radiology has grown dramatically over with intravascular locoregional therapies in the abdomen. In this
the past decade and has expanded the available diagnostic and study, the branching patterns of the major abdominal arteries and
treatment options for veterinary patients. Similarly, the field of associated anatomic landmarks (generally vertebral bodies) were
interventional oncology (IO), with a focus on image-guided ther- described to assist with vascular access and instrument position-
apies for neoplasia, has quickly joined surgery, chemotherapy, and ing during abdominal IO procedures. Consistency in the location
radiation therapy as a 4th pillar of treatment options for oncologic of many of the major abdominal arteries was noted, which will
disease in companion animals. IO combines the use of minimally hopefully decrease anesthesia time and improve understanding of
invasive techniques, advanced instrumentation, image guidance, the normal anatomy, so that abnormal or altered anatomy can be
and creative thinking to allow clinicians to offer treatments that appreciated when it is encountered. 1
can improve pain control, increase quality of life, and potentially Recently ultrasound has been used more commonly during
alter prognosis favorably. Although this discipline is expanding veterinary IO procedures. The main indications for ultrasound
rapidly, the available scientific evidence is limited. However, sig- usage are to guide access to fluid-filled organs for implant place-
nificant work into the evaluation of these procedures is underway. ment or drainage or to access tumors for ablation. Ultrasound is
an excellent imaging modality for these procedures, as it allows
Principles of Interventional Oncology for rapid manipulation of images and real-time assessment of
implant positioning. In veterinary patients, percutaneous access
Imaging to the renal pelvis during antegrade ureteral stent placement is a
common indication for the use of ultrasound guidance. In human
Image guidance allows those individuals performing IO proce- IO procedures, ultrasound is commonly used to obtain vascular
dures to do so in a minimally invasive fashion. It is required for access as well.
clinicians performing IO procedures to have a strong understand- Computed tomography (CT) is a crucial component of the
ing of anatomy and anatomic assessment with various imaging preprocedural assessment of many cases undergoing an IO pro-
modalities. Although there are numerous anatomic descriptions of cedure. At the author’s clinic, in veterinary IO cases being treated
normal anatomy in dogs and cats, very limited data are available with an intravascular technique a contrast-enhanced CT is gener-
for the description of anatomic changes associated with pathologic ally performed before the IO procedure to allow for assessment
conditions that may commonly be treated with IO techniques. both of the vascular supply to a tumor and the extent of the
However, some basic imaging concepts are applicable in most tumor. CT is also being utilized more commonly as a tool for
situations, as the goals of many IO techniques are to either close the assessment of tumor response. This modality is excellent for
down a lumen that is naturally open (e.g., embolization) or open a assessing tumor size and generating tumor volumes both pre- and
lumen that is obstructed by a malignancy (e.g., stenting). postprocedure.
The most commonly used imaging modality in veterinary
medicine for the performance of IO techniques is fluoroscopy. Instrumentation
Fluoroscopy provides a real-time assessment of anatomic struc-
tures and allows clinicians performing these procedures to use Although IO incorporates certain equipment commonly used in
radiopaque instrumentation and contrast medium. Basic fluoro- veterinary practices, much of the instrumentation and devices
scopic equipment and techniques can be used for most stenting used are specific to this discipline. To facilitate the minimally
procedures, but advanced capabilities such as digital subtraction invasive nature that is desired to perform IO techniques, access
angiography and road-mapping are recommended when perform- to organs is obtained and maintained through the use of access
ing assessments of tumoral blood supply or vascular obstructions. needles and catheters and the placement of sheaths. Needles and
It is important to be cognizant of the potential for increased expo- catheters are often similar to what is regularly used in veterinary
sure to radiation when performing these procedures, and appro- practices, but variations in diameter, length, and shape are avail-
priate training in management of radiation exposure should be a able for different indications.
priority for those performing IO procedures. Sheaths can be used multifunctionally and are also available
As stated previously, fluoroscopic vascular guides for per- in different variations. Some of the more popular sheaths used
forming IO procedures are limited. The fluoroscopic abdominal during veterinary IO procedures include those equipped with a
anatomy has recently been described and can be used to assist hemostatic valve and sidearm to allow for contrast injection. These

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