Page 200 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 11 Interventional Oncology 179

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A B
• Fig. 11.3 Intraprocedural images during radiofrequency ablation (RFA) of a prostatic carcinoma in 15-year-
old male castrated mixed breed dog. (A) The RFA electrode has been introduced into the prostate (*) and
ultrasound will be used to determine location and depth. (B) After RFA, the ablation zone can be visually
seen by the alteration in color of the prostate.

because this allows for selection of both carotid arteries and subse- been in the treatment of parathyroid masses in an effort to control
quent bilateral treatment. A coaxial catheterization system is used hypercalcemia. 50–52 Recently, the treatment of a prostatic carci-
to allow for superselection of the nasal blood supply. noma in a dog using RFA was described (Fig. 11.3); as the dog was
undergoing surgery for removal of metastatic lymph nodes, the
53
Ablation RFA procedure was performed via a celiotomy. At surgery, the
electrode was placed into the prostatic tumor using ultrasound-
Ablation is a mainstay of IO treatments in humans, and the appli- guidance and RFA was successfully performed. No signs of resid-
cations in veterinary patients are expanding. General categories ual disease were noted at 8 months post-RFA.
of ablation are chemical and thermal ablation. Chemical abla- MWA uses electromagnetic energy to cause friction and heat,
tion usually focuses on the intralesional injection of liquid agents, also resulting in coagulative necrosis. MWA is a more recently
48
with ethanol being the most common. Thermal ablation is often described option for tumor ablation and there is significant prom-
subdivided into hyperthermic and hypothermic therapies. The ise with this modality, especially for veterinary patients. Higher
hyperthermic ablative techniques include radiofrequency abla- intratumoral temperatures and faster ablations with less char and
tion (RFA), microwave ablation (MWA), high-intensity focused less pain are often achievable with MWA compared with RFA. 54,55
ultrasound (HIFU), and laser ablation, whereas cryoablation is In addition, this modality does not require grounding pads on the
the major hypothermic ablation technique. patient, which is beneficial in smaller animals or animals in which
Most ablation procedures are performed percutaneously with grounding pad placement is difficult and may lead to burn injury.
image guidance, although these procedures can also be performed The use of MWA has recently been evaluated in a few veter-
with minimally invasive or open surgical approaches. For chemi- inary clinical cases. 53,56,57 To date, MWA has been reported to
cal ablation, a needle is usually placed intralesionally and a liquid treat liver neoplasia in five dogs, a metastatic pulmonary lesion
ablation agent (most commonly ethanol) is injected to cause tis- in one dog, and renal carcinoma in one dog. 53,56,57 In the dogs
sue destruction. Thermal ablation techniques such as RFA, MWA, with liver tumors, a ventral celiotomy was performed and MWA
57
and cryoablation are performed after the introduction of a probe was used to treat hepatic lesions directly. No procedural complica-
into the tumor. tions were encountered. A dog with suspected radiation-induced
After introduction of an RFA electrode into a tumor, the scapular and humeral osteosarcoma was diagnosed with hypertro-
electrode is connected to a generator that produces an electrical phic osteopathy after developing a pulmonary metastatic lesion.
current that is transmitted through the electrode into the tumor; The metastatic nodule was treated with thoracoscopically guided
the circuit is completed through grounding pads attached to the MWA. Post-MWA evaluation demonstrated resolution of the
56
patient. The electrical current causes ionic agitation of the tissue, clinical signs associated with hypertrophic osteopathy. Lastly, a
which generates heat resulting in coagulation and cellular necro- dog with a solitary left renal carcinoma was treated with percuta-
sis. Electrode tips come in a variety of lengths and may be just neous MWA via ultrasound guidance. No complications were
53
47
a single tip or an array of expandable tines. The goal of RFA is to reported and the dog is currently 32 months post-MWA with no
treat a margin of grossly normal tissue beyond the tumor to limit evidence of disease. 53
the potential for local recurrence. 48 Cryoablation causes cell death by forming ice crystals within
RFA is the most studied thermal ablation technique in humans cells, through the use of alternating freeze–thaw cycles. Tumors
47
and has been shown to be an excellent treatment option in several of the head have received the most attention in companion ani-
studies. 48,49 Most of the work with RFA in veterinary patients has mals when considering cryoablation. Long-term control of a nasal