Читать книгу Veterinary Surgical Oncology - Группа авторов - Страница 77

In dogs, the trigone of the bladder is the region of the urinary tract most commonly affected by neoplasia; these tumors regularly spread into the urethra (Mutsaers et al. 2003; Saulnier‐Troff et al. 2008). Most tumors of the bladder and urethra are malignant (97%), and transitional cell carcinoma accounts for 87% of all canine bladder and urethral tumors (Norris et al. 1992). Radical surgical resection of tumors in the trigonal region is generally not recommended as recurrence and incontinence are common and bladder necrosis has been reported (Stone et al. 1996; Saulnier‐Troff et al. 2008). Electrosurgical, laser, and vaporization techniques have also been described and carry a concern for urethral rupture (Liptak et al. 2004a). Median survival times for surgical resection alone have been reported as 86–125 days (Lengerich et al. 1992; Norris et al. 1992; Helfand et al. 1994).

Canine prostatic neoplasia carries a poor to grave prognosis due to the effects of local disease and due to a high metastatic rate (Freitag et al. 2007). The most common tumors affecting the prostate are adenocarcinoma and undifferentiated carcinoma, and several treatment modalities, including surgery, radiotherapy, and chemotherapy, have been attempted with mixed success (Freitag et al. 2007). Metastatic rates as high as 89% have been reported (Weisse et al. 2006). Locally, prostatic neoplasia can result in urethral obstruction and subsequent urine retention (Weisse et al. 2006).

While surgical debulking/resection, chemotherapy, and radiotherapy can be the options for initial treatment of nonobstructive bladder or urethral transitional cell carcinoma, these are not good options for immediate relief of complete urethral obstruction secondary to bladder or urethral transitional cell carcinoma. Similarly, prostatic resection and/or radiation may result in local tumor control, but the high metastatic rate and risk of incontinence associated with surgical resection cause many owners not to pursue these options (Goldsmid and Bellenger 1991; Freitag et al. 2007). Palliation of urethral obstructions by the placement of urethral stents has been extensively described in human medicine (Sertcelik et al. 2000; DeVocht et al. 2003; Denys et al. 2004; Eisenberg et al. 2007; Seoane‐Rodriguez et al. 2007; Woo et al. 2008), and experience is increasing in veterinary research (Ko et al. 2002; Yoon et al. 2006; Crisóstomo et al. 2007) and clinical medicine (Weisse et al. 2006; Newman et al. 2009; Christensen et al. 2010; McMillan et al. 2012; Blackburn et al. 2013; Brace et al. 2014). This technique is generally well tolerated and is one of the simpler and most commonly performed IO procedures in veterinary medicine (Figure 3.2).

The major complication described for urethral stents is urinary incontinence, which has occurred in 26–37% of dogs (McMillan et al. 2012; Blackburn et al. 2013). Most owners can manage this by frequent walks and potentially the use of a diaper. It is important to determine if urinary incontinence is something that an owner feels comfortable handling after stent placement because it occurs relatively frequently. Other complications that may occur with stent placement include migration of the stent, technical errors, stranguria poststenting, tearing of the urethra, and growth of tumor around or into the stent.

The use of urethral stents to treat bladder, urethra, and prostatic neoplasia in a clinical setting has been evaluated in a few canine case series (Weisse et al. 2006; McMillan et al. 2012; Blackburn et al. 2013). In the first canine case series, obstruction was relieved in all 12 dogs immediately after the procedure, and 11 of 12 dogs were urinating voluntarily. Incontinence and stranguria after stent placement were noted in several cases; however, 10 of 12 dogs were considered to have a fair to excellent outcome (Weisse et al. 2006). In two other canine case series, the median survival time was 78 days in both studies. In one study, the use of nonsteroidal anti‐inflammatories and chemotherapy significantly increased median survival time to 251 days. A balloon‐expandable metallic stent was successfully used to relieve urethral obstruction in a cat diagnosed with urothelial carcinoma (Newman et al. 2009). Evaluation of long‐term outcome was not possible as the cat developed progressive azotemia and was euthanized (Newman et al. 2009). Since that report, five other feline urethral stent cases have been published and early success was noted. In male cats that have not undergone a perineal urethrostomy, stents must be placed antegrade due to the size of the stent delivery system.