Malignant Obstructions

Malignant Obstructions

Tracheal Cancer

Bladder/Urethra/Prostate Cancer

Ureteral Obstruction Secondary to Cancer

Vascular Obstruction Secondary to Cancer

Colorectal Cancer


Tracheal Cancer

Tracheal stenting may be an option for obstructions of the trachea secondary to cancer. For cases of tracheal cancer, the purpose of the stent is to palliate your pet’s clinical signs (difficulty breathing) and to make him or her more comfortable by allowing easier passage of oxygen to the lungs.

Background Information
Tracheal neoplasia is rare in dogs and cats, and the most common clinical sign is labored breathing or respiratory distress. (Brown 2003, Brown 2005) Tracheal neoplasia has mostly been characterized in case reports, however, a few case series can be found in the veterinary literature. In the earliest case series, 16 canine and 7 feline tracheal tumors were identified. (Carlisle 1991) The most common tumors identified were osteochrondroma and epithelial malignancies. (Carlisle 1991) In a separate study evaluating tracheal masses in cats, 3/7 masses were found to be lymphoma and 1 case each of adenocarcinoma, squamous cell carcinoma, lymphoplasmacytic inflammation and lymphoid hyperplasia were identified. (Jakubiak 2005)

Several treatment options exist for tracheal masses. Surgery is considered the treatment of choice for non-lymphomatous tracheal masses. Surgical resection and anastomosis can be performed in select cases where it is deemed to be possible and appropriate. In particular, resection and anastomosis should be considered in cases where the mass is annular or full thickness through the tracheal wall. A new therapy involving endoscopic debulking of the mass has proven beneficial in improving respiration in certain cases and is currently being performed at UC Davis by Dr. Johnson. If lymphoma is diagnosed on biopsy, chemotherapy and/or radiation therapy may also be considered. In a series of 4 cats with tracheal lymphoma, a complete response was seen in 2 cats that underwent either chemotherapy alone or chemotherapy combined with radiation therapy.

In cases that surgery, bronchoscopic reduction, or chemotherapy and radiation therapy are not considered good treatment options or not elected by the owner, palliative stenting of the trachea to relieve clinical signs can be considered. In the only clinical report of tracheal stenting to treat a cat with a tracheal adenocarcinoma, tracheal stenting alleviated clinical signs, and the cat maintained a good quality of life until metastatic disease was noted. (Culp 2007)

Diagnostic and Treatment Steps at UC Davis
At the first examination, the following will be obtained:

  1. Physical examination
  2. Minimum database
  3. Neck and chest radiographs
  4. Fluoroscopy to determine the length of tracheal narrowing secondary to the mass
  5. Anesthesia for airway assessment:
    • Upper airway examination
    • Full lower airway examination by bronchoscopy
    • Bronchoalveolar lavage with cytology and culture
  6. Tracheal measurements
  • Brown MR, Rogers KS. Primary tracheal tumors in dogs and cats. Comp Cont Educ Pract 2003;25:854-859.
  • Brown MR, Rogers KS, Mansell KJ, et al. Primary intratracheal lymphosarcoma in four cats. JAAHA 2003;39:468-472.
  • Carlisle CH, Biery DN, Thrall DE. Tracheal and laryngeal tumors in the dog and cat: literature review and 13 additional patients. Vet Radiol Ultrasoun 1991;32:229-235.
  • Culp WTN, Weisse C, Cole SG, et al. Intraluminal tracheal stenting for treatment of tracheal narrowing in three cats. Vet Surg 2007;36:107-113.
  • Jakubiak MJ, Siedlecki CT, Zenger E, et al. Laryngeal, laryngotracheal, and tracheal masses in cats: 27 cases (1998-2003) JAAHA 2005;41:310-316.

Urethra/Bladder/Prostate Cancer

The urethra is the tube that carries urine from the bladder and expels it outside of the body. Tumors are commonly found in the bladder, urethra and prostate (males) in locations that can cause blockage of the urethra with a subsequent inability to expel urine. Several treatment options including oral medications, chemotherapy, radiation therapy and surgery have been utilized to treat these tumors. These treatments may be insufficient to treat the life-threatening complications associated with a complete blockage of the urethra.

In certain cases, the placement of a urethral stent may be necessary to allow for relief of the urethral obstruction. If your pet suffers from cancer of the bladder, urethra or prostate, please consult with a member of the oncology service to determine if a urethral stent may be an appropriate treatment option.

Background Information
Malignant obstruction of the urethra can originate from the bladder, urethra or prostate. Transitional cell carcinoma is the most common tumor affecting the urethra and bladder of dogs. (Mutsaers 2003) The most commonly diagnosed neoplasms affecting the prostate include adenocarcinoma, undifferentiated carcinoma and transitional cell carcinoma. (Bell 1991, Teske 2002, Vlasin 2006, Bradbury 2009) Traditional treatment options for tumors causing obstruction of the urethra, generally fall into three general categories: surgery, chemotherapy and radiation therapy.

Chemotherapy may be included in the treatment of tumors causing malignant urethral obstruction. (Mutsaers 2003, Freitag 2007) Additionally, radiation therapy is often utilized to treat prostatic neoplasia in dogs and may be considered for urethral and bladder tumors as well.

While surgical debulking/resection, chemotherapy and radiotherapy may be potential treatment options for initial treatment of non-obstructive urethral neoplasia, these are not good options for immediate relief of complete urethral obstruction secondary to neoplasia. Palliation of urethral obstruction by the placement of a urethral stent has been extensively described in human clinical medicine (Sertcelik 2000, DeVocht 2003) and experience is increasing in veterinary clinical medicine. (Weisse 2006)

Diagnostic and Treatment Steps at UC Davis
Initial diagnostics will include bloodwork (CBC/chemistry panel), chest radiographs, abdominal ultrasound, urinalysis, urine culture and cystourethroscopy. Biopsies will likely be obtained during cystourethroscopy, and stent measurements may be made during that time utilizing fluoroscopy. The stent may be placed at the time of cystourethroscopy (depending on the size needed) or during a 2nd anesthetic event performed a few days later. Serial evaluation of bloodwork, urinalysis and urine culture will likely be recommended. Cystourethroscopy may need to be performed at a future date to assess stent patency and development of tumor in-growth through the stent.

  • Bell FW, Klausner JS, Hayden DW, et al. Clinical and pathologic features of prostatic adenocarcinoma in sexually intact and castrated dogs: 31 cases (1970–1987). JAVMA 1991;199:1623-1630.
  • Bradbury CA, Westropp JL, Pollard RE. Relationship between prostatomegaly, prostatic mineralization, and cytologic diagnosis. Vet Radiol Ultrasoun 2009;50:167-171.
  • DeVocht TF, VanVenrooij, Boon TA. Self-expanding stent insertion for urethral strictures: a 10-year follow-up. BJU International 2003;91:627-630.
  • Freitag T, Jeram RM, Walker AM, et al. Surgical management of common canine prostatic conditions. Compen Cont Educ Pract 2007;29:656-672.
  • Mutsaers AJ, Widmer WR, Knapp DW. Canine transitional cell carcinoma. JVIM 2003;17:136-144.
  • Sertcelik N, Sagnak L, Imamoglu A, Temel M, et al. The use of self-expanding metallic urethral stents in the treatment of recurrent bulbuar urethral strictures: long-term results. BJU International 2000;86:686-689.Teske E. Naan EC, van Dijk  EM, et al. Canine prostate carcinoma: epidemiological evidence of an increased risk in castrated dogs. Molecular and Cellular Endocrinology 2002;197:251-255.
  • Vlasin M, Rauser P, Fichtel T, et al. Subtotal intracapsular prostatectomy as a useful treatment for advanced-stage prostatic malignancies. JSAP 2006;47:512-516.
  • Weisse C, Berent A, Todd K, et al. Evaluation of palliative stenting for management of malignant urethral obstructions in dogs. JAVMA 2006;229:226-234.

Ureteral Obstruction Secondary to Cancer

Dogs and cats have two ureters. The ureter is the tube connecting the kidney to the bladder and has the responsibility of carrying urine to the bladder after it is formed in the kidney. Malignant (cancerous) obstruction of the ureter is generally secondary to cancer that originates in the bladder or urethra and extends over the ureteral opening into the bladder.  Obstruction can prevent urine from travelling to the bladder which may be a life-threatening condition.

Generally, for malignant ureteral obstructions, stenting involves the placement of a tube within the ureter that extends from the kidney to the bladder to allow for the passage of urine. This is performed through the skin without an incision which allows for minimally invasive placemetn of a stent.

Background Information

Ureteral obstruction secondary to neoplasia is rare. Primary ureteral tumors that occur cranial to the ureterovesicular junction are generally treated with surgical removal. However, ureteral obstruction secondary to a tumor that originates in the bladder or urethra and encompasses the ureterovesicular junction is often not as amendable to resection. The use of ureteral stents to relieve a ureteral obstruction is an important treatment option in humans, and both retrograde and antegrade techniques (utilizing nephrostomy) have been described.

A technique for percutaneous placement of ureteral stents in dogs with malignant ureteral obstruction was recently reported. (Berent 2011)  In this series of 12 dogs, the obstructed ureters were accessed in antegrade fashion through the placement of a needle within the renal pelvis (successful in 11/12 dogs); ultrasound-guidance was utilized to position the needle appropriately. In all cases, a double-pigtail stent was placed with the goal of leaving the cranial pigtail in the renal pelvis and the caudal pigtail in the urinary bladder (beyond the obstruction). All patients with azotemia demonstrated improvement in BUN and creatinine concentrations post-stent placement. In the 10 patients that underwent abdominal ultrasound post-stent placement, all were demonstrated to have decreased severity of hydronephrosis and hydroureter. Overall, ureteral stent placement was determined to be safe and well tolerated in that cohort of dogs. (Berent 2011)

  • Berent AC, Weisse C, Beal MW, et al. Use of indwelling, double-pigtail stents for treatment of malignant ureteral obstruction in dogs: 12 cases (2006-2009). JAVMA 2011;238:1017-1025.

Vascular Obstruction Secondary to Cancer

Blood vessels can become blocked by tumors resulting in an inability of blood to flow through those vessels. Signs may develop secondary to poor blood flow or a decreased ability for blood to return to the heart. Stents can be placed into the blood vessel to open the blood vessel and allow blood to flow more effectively.

Background Information

Vascular stents can be placed as a palliative means of recanalizing vascular obstructions that occur secondary to neoplasia. (Mónaco 2003, Novellas 2009) After placement of the stent, clinical signs often resolve. (Mónaco 2003, Novellas 2009) Malignancy is the cause of superior vena cava syndrome (obstruction of the superior vena cava causing prevention of venous return) in 90% of human cases and the placement of vascular stents has become the treatment of choice. (Mónaco 2003)

Budd-Chiari syndrome occurs when venous flow at the level of the hepatic veins and/or vena cava is obstructed. (Cura 2009, Xue 2009) The success rate of stent placement in humans as manifested by alleviation of effusion, ascites and hepatomegaly has been reported to be up to 97%. (Qiao 2005) A recent paper evaluated stent placement in three dogs with Budd-Chiari syndrome. (Schlicksup 2009) All dogs had confirmed or suspected neoplasia causing Budd-Chiari syndrome. A stent or stents were placed into the left hepatic vein and/or the caudal vena cava to relieve the obstruction. All dogs experienced relief of clinical signs and survival time ranged from 7-20 months. (Schlicksup 2009)

  • Cura M, Haskal Z, Lopera J. Diagnostic and interventional radiology for Budd-Chiari syndrome. Radiographics 2009;29:669-681.
  • Mónaco RG, Bertoni H, Pallota G, et al. Use of self-expanding vascular endoprostheses in superior vena cava syndrome. Eur J Cardio-Thorac 2003;24:208-211.
  • Novellas S, Denys A, Bize P, et al. Palliative portal vein stent placement in malignant and symptomatic extrinsic portal vein stenosis or occlusion. Cardiovasc Inter Rad 2009;32:462-470.
  • Qiao T, Liu C, Liu C, et al. Interventional endovascular treatment of Budd-Chiari syndrome with long-term follow-up. Swiss Med Wkly 2005; 135:318-326.
  • Schlicksup MD, Weisse CW, Berent AC, et al. Use of endovascular stents in three dogs with Budd-Chiari syndrome. JAVMA 2009;235:544-550.

Colorectal Cancer

Colon cancer in veterinary patients is most often treated by surgical removal. While surgery is associated with some morbidity, successful outcomes can be obtained. In very select cases of colorectal cancer, the tumor is too large to be removed or is located in an area preventing complete removal. Medical management to ease the expulsion of feces may still be tried in these cases but is often unsuccessful. 

In cases where a patient is not successfully treated with medical and/or surgical management, the placement of a colonic stent may be considered. A metal or metal-alloy stent that generates outward force can provide an opening in the colon to allow for the passage of feces. In most cases, medical management post-stent placement is still required, however, the goal of the procedure is to significantly improve the pet’s quality of life.

In male dogs that develop prostate disease, the colon can occasionally become obstructed as well. When prostate disease is severe enough, the prostate may grow large enough to compress the colon and prevent normal defecation. A colonic stent may be considered in certain cases of colonic obstruction secondary to prostatic disease as well.

Background InformationThe most common masses affecting the colon and rectum of the dog include adenocarcinoma, adenomatous polyps and carcinoma in situ. (Patnaik 1977, Patnaik 1980, Holt 1985, Birchard 1986) Surgery is considered the treatment of choice for most non-lymphomatous tumors and several surgical treatments have been developed to resect both small and large tumors. (Anson 1988,  Aronson 2006, Yoon 2008) Chemotherapy is considered in cases of colorectal lymphoma.

Colorectal stenting has been extensively described in human medicine for the treatment of both benign and malignant colorectal tumors. Colorectal stents in humans have 2 primary indications: as a “bridge to surgery” which allows for patient stabilization prior to undergoing an elective procedure or to palliate clinical signs. (Davies 2004, Watt 2007, Kim 2008) In the “bridge to surgery” group, stent placement prior to undergoing an elective procedure has been shown to improve outcome (less complications, less unnecessary operations). (Santos-Martinez 2002) As opposed to major surgical resection or colostomy stoma formation, some patients elect to have a stent placed to palliate clinical signs. (Athreya 2006)

Colonic stenting has been reported in 2 cats and 1 dog. (Hume 2006, Culp 2011) In one cat, clinical signs were limited to mechanical obstruction of the colon, despite the presence of suspected pulmonary metastatic disease at the initial evaluation. The clinical signs improved after stent placement in this cat, and tenesmus was rarely observed; fecal incontinence was not reported. Despite the presence of multiorgan metastasis at the time of euthanasia (the colonic tumor was noted to be an adenocarcinoma), the cat survived for 274 days post-stent placement. (Hume 2006)  In the single canine case report, successful stent placement was noted and clinical signs improved for just over 200 days. (Culp 2011)

Diagnostic and Treatment Steps at UC Davis
Initial diagnostics will include bloodwork (CBC/chemistry panel), chest radiographs, abdominal radiographs, abdominal ultrasound, and colonoscopy. Biopsies will be obtained during colonoscopy. Stent measurements will likely be made with a combination of fluoroscopy (+/- contrast) and colonoscopy. When the size of the stent has been determined, the stent is ordered and placed at a future time. Serial colonoscopy may need to be performed to assess for stent patency and tumor in-growth through the stent.

  • Anson LW, Betts CW, Stone EA. A retrospective evaluation of the rectal pull-through technique. Vet Surg 1988;17:141-146.
  • Aronson L. Rectum and Anus. In Textbook of Small Animal Surgery pp 682-708. 2006. 3rd Edition. Douglas Slatter (editor). Saunders: Philadelphia, PA.
  • Athreya S, Moss J, Urquhart, et al. Colorectal stenting for colonic obstruction: the indications, complications, effectiveness and outcome-5-year review. Eur J Radiol 2006;60:91-94.
  • Birchard SJ, Couto CG, Johnson S. Nonlypmhoid intestinal neoplasia in 32 dogs and 14 cats. JAAHA 1985;22:533-537.
  • Culp WTN, MacPhail CM, Perry JA, et al. Use of a nitinol stent to palliate a colorectal neoplastic obstruction in a dog. JAVMA 2011;239:222-227.
  • Davies RJ, Barros D’Sa I, Lucarotti ME, et al. Bowel function following insertion of self-expanding metallic stents for palliation of colorectal cancer. Colorectal Disease 2004;7:251-253.
  • Holt PE, Lucke VM. Rectal neoplasia in the dog: a clinicopathological review of 31 cases. Vet Rec 1985;116:400-405.
  • Hume DZ, Solomon JA, Weisse CW. Palliative use of a stent for colonic obstruction caused by adenocarcinoma in two cats. JAVMA 2006;228:392-396.
  • Kim H, Kim SH, Choi SY, et al. Fluoroscopically guided placement of self-expandable metallic stents and stent-grafts in the treatment of acute malignant colorectal obstruction J Vasc Interv Radiol 2008;19:1709-1716.
  • Martinez-Santos C, Lobato RF, Fradejas JM, et al. Self-expandable stent before elective surgery vs. emergency surgery for the treatment of malignant colorectal obstructions: comparison of primary anastomosis and morbidity rates. Dis Colon Rectum 2002;45:401-406.
  • Patnaik AK, Hurvitz AI, Johnson GF. Canine gastrointestinal neoplasms. Vet Pathol 1977;14:547-555.
  • Patnaik AK, Hurvitz AI, Johnson GF. Canine intestinal adenocarcinoma and carcinoid. Vet Pathol 1980;17:149-163.
  • Watt AM, Faragher IG, Griffin TT, et al. Self-expanding metallic stents for relieving malignant colorectal obstruction. Annals of Surgery 2007;246:24-3.
  • Yoon H, Mann FA. Bilateral pubic and ischial osteotomy for surgical management of caudal colonic and rectal masses in six dogs and a cat. JAVMA 2008;232:1016-1020.