Figure 3.3 Colorectal stent (neoplastic obstruction). In this dog, a stent was placed to palliate clinical signs associated with a large annular colorectal neoplasm that extended for 8 cm and was causing colorectal obstruction. This radiograph was taken 190 days after stent placement.

      Esophageal Neoplasia

      Greater than 50% of human patients will have unresectable esophageal neoplasia at the time of diagnosis (Burstow et al. 2009). The median survival time for these patients is between three and six months, and palliative treatments are often pursued due to the grave prognosis (Sabharwal et al. 2005; Wilkes et al. 2007). The palliation of dysphagia is essential to the patient’s quality of life, and esophageal stents are often placed in an attempt to achieve this goal (Sabharwal et al. 2005; Wilkes et al. 2007; Burstow et al. 2009). Esophageal stents have been shown to be an effective means of relieving malignant dysphagia secondary to malignant obstructions (Sabharwal et al. 2005; Wilkes et al. 2007; Burstow et al. 2009).

      The use of esophageal stents in companion animals is controversial as the associated complications can be severe. Currently, only a single case report of an esophageal stent for relief of a malignant obstruction (squamous cell carcinoma) has been reported (Hansen et al. 2012). The placement of an esophageal stent, in that case, relieved the obstruction and improved clinical signs.

      Biliary Neoplasia

      Obstruction of the biliary tree can occur from both primary hepatobiliary disease as well as external compression from other abdominal neoplasia (Moss et al. 2007; Lee 2009). While surgical bypass and the placement of both plastic and metal stents have been described in human patients, the endoscopic placement of metal stents is considered the treatment of choice (Moss et al. 2007; Lee 2009). However, metal stents can become occluded, and research toward developing drug‐eluting stents to prevent occlusion and to deliver local chemotherapy is being conducted (Lee 2009). Biliary stenting (using red‐rubber catheters) for relief of benign obstructions (mostly pancreatitis) in dogs and cats has been described (Mayhew et al. 2006; Mayhew and Weisse 2008); however, reports on the treatment of malignant obstructions with stents are lacking. In the author’s practice, biliary stents have been placed for malignant obstructions extending from the common bile duct into the duodenum to allow for bile drainage. The stents have been placed surgically; however, investigation into minimally invasive options is underway.

      Percutaneous Drainage

      Malignant Body Cavity Effusions

Interventional radiologists are often called on to relieve malignant effusions within the thoracic and abdominal cavities. In cases of malignant effusions, the goal of placing a catheter is palliation of the associated adverse clinical signs. The catheter may be placed temporarily or attached to an external or subcutaneous port for long‐term drainage. Placement of the drainage catheter does not treat the primary disease, and recurrence of the pleural or abdominal fluid may be rapid. Long‐term placement of a catheter with a port may be indicated in many cases of malignant effusion. A case series of 10 cases (6 dogs, 4 cats) undergoing placement of a port and intrathoracic drainage catheter to treat pleural effusion have been reported (Brooks and Hardie 2011). Only one case in that cohort was confirmed to have a pleural effusion secondary to neoplasia, and the follow‐up time was short as the patient was euthanized after six days due to progression of disease.

      Many interventional radiologists consider pigtail catheters placed with ultrasound guidance, the gold standard when treating malignant effusions (Klein et al. 1995; Parulekar et al. 2001; Liang et al. 2009). In human patients with malignant thoracic effusions, small‐bore catheters (such as pigtail catheters) have demonstrated similar outcomes when compared to large‐bore chest tubes (Clementsen et al. 1998; Parulekar et al. 2001). Patients undergoing removal of thoracic effusions with small‐bore tubes were also found to be more comfortable (Clementsen et al. 1998).

      A modified Seldinger technique has been used to place small‐bore chest drains in the thorax to relieve effusions in dogs and cats (Valtolina and Adamantos 2009). While only 1 of 20 animals had a malignant effusion, the study revealed that these chest drains were placed easily and effectively by people with varying levels of experience (Valtolina and Adamantos 2009). Anesthesia was not necessary for drain placement in any of the cases, and 24 of 29 chest drains were placed in less than 10 minutes (Valtolina and Adamantos 2009). In the author’s practice, a minimally invasive technique (using a modified Seldinger technique) is utilized to place permanent thoracic drainage tubes connected to a subcutaneous port. For this procedure, the thoracic drain (multi‐fenestrated catheter) is placed through a sheath (placed intercostally) and is tunneled subcutaneously to a port that is introduced under the skin through a small incision.

      Other Drainages

      Percutaneous drainage of the gallbladder and the percutaneous placement of nephrostomy tubes to divert urine flow may be indicated with certain neoplastic processes. Both ultrasound and fluoroscopic guidance have been used to place these tubes (Morgan and Adam 2001; Covey and Brown 2006; Saad et al. 2009; Uppot 2009). These techniques may be useful as temporary palliative measures to stabilize patients prior to a definitive surgery.

      Minimally invasive placement of nephrostomy and cholecystostomy tubes is being performed in veterinary clinics, but reports are lacking. In a canine cadaver study, pigtail catheters were placed in gallbladders using both ultrasound guidance and laparoscopic guidance, and the two techniques were compared (Murphy et al. 2007). The laparoscopic‐guided technique was found to be significantly more likely to result in successful placement of the pigtail catheter (Murphy et al. 2007). Percutaneous biliary drainage has been shown to be safe and effective in humans (van Delden and Laméris 2008), and further investigation of these procedures in veterinary cases is necessary.

      Tumor Ablation

      According to Simon and colleagues (Simon et al. 2005), tumor ablation is “the direct application of chemical or thermal therapies to a tumor to achieve eradication or substantial tumor destruction.” The most commonly used forms of tumor ablation include RFA, cryoablation, microwave ablation, laser ablation,