Recurrent Urethral Fibroepithelial Polyps in a Golden Retriever

Introduction

Fibroepithelial polyps (FEPs) are rare tumors of the urinary tract. They occur in humans, most commonly arising in the posterior urethra of males. They can lead to voiding dysfunction and urethral obstruction, but rarely recur after removal. Urinary tract polyps seem to be similarly rare but less well described in the dog, with most described as arising from the ureter or bladder. The following case is the first report of urethral fibroepithelial polyps in a male dog and the first report of recurrent polyp formation.

The purpose of this case report is to provide information on the difficulties in treatment of recurrent urethral polyps and use of non-surgical methods to manage them.

Case Report

A 2 yr old castrated male golden retriever was referred to the Virginia-Maryland Regional College of Veterinary Medicine Veterinary Teaching Hospital (VMRCVM-VTH) for hematuria, pollakiuria, and stranguria with urethral obstruction, requiring daily catheterization to empty the bladder. A previous episode of hemorrhagic cystitis and urethral obstruction due to blood clots was diagnosed 7 mo prior at the VMRCVM-VTH, which was treated with antibiotics and multiple urinary catheterizations. Diagnostics performed at that time at the VMRCVM-VTH included complete blood count, biochemical profile, coagulation profile, urethrocystography, exploratory cystotomy with retrograde catheterization of the ureters, intraoperative antegrade urethroscopy, urine and bladder wall aerobic and mycoplasma cultures, and bladder histopathology. Full-thickness bladder histopathology revealed a moderately severe, subacute, serohemorrhagic, neutrophilic cystitis. Treatments for the cystitis included a one-time bladder infusion of 750 μg of prostaglandin F2α diluted in 50 mL of normal saline and oral amoxicillin (17 mg/kg per os [PO] q 8 hr) for 4 wk. Antibiotic therapy was continued because of the degree of inflammation present and due to multiple instrumentation procedures and surgical exploration performed at the initial visit to the VMRCVM-VTH. The patient recovered from this episode within 1 mo based on a normal physical examination, urinalysis, and negative aerobic urine culture conducted by the referring veterinarian. To investigate the current episode of urethral obstruction, a double-contrast urethrocystogram was performed. A large, irregular, pedunculated, intraluminal filling defect was present in the prostatic urethra. Additional injections of iodinated contrast medium resulted in inversion of this mass proximally into the trigone region of the bladder with the base remaining in the urethra (Figures 1A, B). Fluoroscopic-guided retrieval of multiple masses was performed with a four-wire spiral stone retrieval basket^a by advancing it into the bladder and/or urethra, entrapping the mass within the basket, and applying gentle traction (Figure 2). Complete removal of all masses could not be confirmed by urethrocystography. Self-limiting hematuria occurred after the procedure, and the dog was maintained with an indwelling urinary catheter.

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Tissues removed were polypoid in appearance with an elongated shape, tapering stalk, and smooth mucosal surface (Figure 2). Histologically, the masses were described as urethra covered by normal transitional epithelium with focal areas of hyperplasia, erosion, and ulceration. Thick, loose, fibrous connective tissue with abundant collagen, diffuse edema, and a normal supporting vascular network comprised the submucosa. Diffuse, mild inflammation comprised of lymphocytes and macrophages was present. Those findings were consistent with a diagnosis of mild urethritis and urethral FEPs (Figures 3 A, B). An exploratory cystotomy and proximal urethrotomy were performed through a ventral approach to remove any remaining polyps, but none were found. Full-thickness biopsies of the bladder and proximal urethral were performed. Histologically, a mild cystitis and urethritis were present. Aerobic bacterial and mycoplasma cultures of the urine, bladder wall, and polyps were negative. However, the dog had received antibiotics prior to referral; thus, an underlying infection could not be ruled out. After 24 hr, the indwelling catheter was removed. The patient was prescribed piroxicam^b (0.25 mg/kg PO q 6 hr), misoprostol^c (3 μg/kg PO q 12 hr), and amoxicillin^d (20 mg/kg PO q 8 hr) for 4 wk. The owner reported resolution of stranguria 10 days after surgery.

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Reexamination, including urinalysis, aerobic bacterial urine culture, and urethrocystography, was unremarkable 4 wk later. Misoprostol and piroxicam were continued for 4 additional wk. However, 5 wk later, stranguria, pollakiuria, and hematuria recurred. Recurrent polyps of the pelvic and prostatic urethra were confirmed with urethrocystoscopy in similar locations to the previously removed polyps. Polyps were removed endoscopically using a spiral stone basket to avulse them, with the exception of the largest polyp, which was removed by traction avulsion using hemostats via a ventral approach cystotomy and urethrotomy. Histologic diagnosis of the removed tissues was again FEPs. Staphylococcus pseudintermedius was cultured from the urine, and antibiotic therapy was initiated based on sensitivity results. Piroxicam and misoprostol were reinstituted in addition to oral amoxicillin (20 mg/kg PO q 8 hr) for 4 wk. Clinical signs resolved, but the dog became urinary incontinent within 10 days after discharge, which was thought to be due to urethral sphincter damage related to the multiple cystotomies and proximal urethrotomies. Phenylpropanolamine^e (25 mg PO q 8 hr) was administered for urinary incontinence, which resolved within 1 wk of initiation of therapy. Four weeks later, the infection was resolved, but urethrocystoscopy revealed a small apical bladder diverticulum and white, fibrous-appearing tissue at the base of the previous polyp sites. Piroxicam, misoprostol, and phenylpropanolamine (25 mg PO q 8 hr) were continued as previously prescribed. Reexaminations, including aerobic bacterial urine culture and urethrocystoscopy, were performed q 1–3 mo for 2 yr (at which point piroxicam and misoprostol were discontinued) then q 6 mo for 1 yr, after which no further reexaminations were performed for the ensuing 2.5 yr. Two polyps recurred within the following year; a 2 mm polyp was removed endoscopically with a basket, and one polyp passed in the urine and was collected by the owner. All polyps removed at the VMRCVM-VTH were located in similar locations within the proximal and prostatic urethra. No further urinary tract infections were documented based on aerobic urine cultures on multiple occasions either at the VMRCVM-VTH or by the referring veterinarian.

Approximately 7 yr after the initial diagnosis of urethral FEPs (5 yr since the last polyp recurrence), clinical signs returned and multiple necrotic, infected polyps were again present (confirmed by histopathology and culture) in the urethra. Urine culture was positive for S. pseudintermedius. The polyps were removed by a combination of avulsion using a stone retrieval basket and laser resection^f. Recovery was uneventful and clinical signs resolved within several days of receiving an oral antibiotic (20 mg/kg amoxicillin PO q 8 hr for 3 days). Amoxicillin treatment was continued for a longer duration by the referring veterinarian. A urine culture for Mycoplasma was negative for growth. No further contact with either the owner or referring veterinarian has occurred in the last 1.5 yr.

Discussion

Urethral tumors of all types are uncommon in the dog. In one study of 966,000 dogs, only 40 urethral tumors were identified. The majority of those tumors were malignant and occurred in females.^1,2 Only three reports of FEPs of the urinary tract in dogs can be identified, which consist of six dogs.^3–5 Five dogs in those reports had a ureteral polyp, and one dog had a urethral polyp.^3–4 An additional 16 FEPs in dogs were identified in a study of the classification of canine urinary bladder urothelial tumors, but clinical information pertaining to those cases was not available.⁶ Reichele et al. (2003) treated all dogs with surgical excision. In that series, the etiology was not identified; however, either benign neoplasm or a chronic inflammatory reaction was suspected.⁵ Similarly, Elwick et al. (2003) described the use of a laser for the treatment of a single obstructive urethral polyp in a female dog.⁴ In that case, inflammation associated with chronic lower urinary tract infection was the suspected etiology. The polyp did not recur, and there was complete resolution of lower urinary tract signs. To the authors’ knowledge, the case report described herein is the only published report of recurrent urethral polyps in a dog.

FEPs of the lower urinary tract of humans occur most commonly in the posterior urethra and almost exclusively in males.^7–9 FEPs are thought to be either a development error in the invagination process of submucosal glandular material of the inner zone of the prostate gland or a hamartomatous growth.^7,10,11 Surgical excision is the recommend treatment in humans. Recurrence rate after surgical excision is low with no recurrence of polyp growth in 10 of 10 male patients in one report.^8–10,12 The patient described herein is the first reported case of FEPs in a young male dog, a presentation similar to that in humans but with frequent recurrences. Polypoid cystitis is the more common presentation of polyps associated with lower urinary tract disease in the dog.¹³ It is unusual for polypoid cystitis to result in either obstructive uropathy or to involve the urethra. In this case, no specific underlying cause for the mucosal inflammation was identified. Although infection with S. pseudintermedius was only documented on two occasions when polyps were present and chronic or recurrent bacterial infection could have been an underlying cause of polyp formation. Infection with other organisms such as fungi, l-form bacteria, or viruses seems unlikely. Fungi that infect the urinary tract, such as Candida spp. are relatively easy to identify with urinalysis, grow readily on bacterial culture media, and would have been detected on the multiple histologic examinations were performed on urinary tissues. The study authors did not investigate possible infection with l-form bacteria because those have not been described as uropathogens of dogs. Viral infection as an inciting cause is an intriguing possibility that the study authors did not investigate. Currently, there are no known viral infections of the bladder that cause either cystitis or urethritis in dogs. Piroxicam induces remission in some dogs with transitional cell carcinoma of the urinary bladder. That may occur either through induction of apoptosis or reduction in growth factor expression.¹⁴ Those effects were considerations in the study authors decision to use piroxicam in this dog. The authors chose to administer misoprotsol and prostaglandins because they have been shown to be effective in the treatment of sterile hemorrhagic cystitis associated with cyclophosphamide administration in humans and are thought to have cytoprotective effects that benefit the bladder mucosa.^15,16

Surgical removal of the polyps proved difficult due to their location within the urethra and the risk of complications, which included urethral stricture formation and urethral sphincter incompetence. Urinary incontinence did develop in this patient but was managed by use of an α-agonist with good results. The restricted working area within the urethra made endoscopic removal of the polyps difficult; however, those procedures appeared to be useful in the long-term management of this case. Recurrence of polyps seemed mainly due to either incomplete resection or recurrent mucosal inflammation.

Conclusion

Urethral polyps are an uncommon cause of lower urinary tract signs, and recurrence after removal is rare. Removal can be accomplished in numerous ways; fluoroscopy, endoscopy, and a holmium yttrium aluminum garnet laser proved to be useful minimally-invasive methods of managing recurrent polyps in this dog. It is uncertain if antibiotics and/or piroxicam were effective in minimizing recurrence.