Urethral Stricture and Perineal Urethrostomy in a Ferret
Erica Rangel
Basic Science Advisor: Dr. Jamie Morrisey
Clinical Advisor: Dr. Andrew Cushing
Senior Seminar Paper
Cornell University College of Veterinary Medicine
January 22, 2014
KEY WORDS: ferret, urinary, obstruction, urethra, stricture, perineal urethrostomy
ABSTRACT: A 3.5-year-old male castrated ferret was initially seen at Cornell
University Hospital for Animals (CUHA) for urethral obstruction due to cystine
urolithiasis, which was surgically corrected with a cystotomy and urethrostomy. The
ferret twice returned post-operatively for transient urinary obstruction at which times
diagnostic testing ruled out urolithiasis and infection. The patient presented most recently
for a 24-hour history of stranguria that could not be pharmacologically resolved. Physical
examination revealed moderate abdominal distension and a painful, turgid, nonexpressable bladder. An abdominal ultrasound was highly suggestive of a perineal hernia
with bladder prolapse. A cystopexy was performed and the urethra became patent, but by
the following morning the patient had reobstructed. A repeat ultrasound confirmed an
intact pexy site. A contrast cystogram revealed a severely dilitated pelvic urethra
secondary to a penile urethral stricture. The patient was again taken to surgery for a
microscope-aided perineal urethrostomy. Surgery was successful.
INTRODUCTION: A 3.5-year-old male castrated ferret (Mustela putorious furo),
originally presented to the Cornell University Hospital for Animals (CUHA) Emergency
service on 9/15/2012 for stranguria and was acidotic, hyperkalemic and azotemic on
presentation. The ferret was diagnosed with urinary obstruction secondary to cystine
urolithiasis, which was surgically corrected with a cystotomy and urethrotomy. The
patient was discharged with a guarded prognosis and high likelihood of reobstruction.
The patient represented for additional episodes of urinary obstruction two and
nine months post-operatively. On those visits, diagnostics revealed that the patient was
negative for uroliths or urinary tract infection. The owners declined further diagnostic
work up at these times, and a presumptive diagnosis of urethral stricture was made. The
patient’s urethra became patent with urinary catheterization and conservative medical
management. The ferret was maintained at home for six months with an oral treatment
regimen to reduce inflammation (meloxicam 0.3 mg q24) and to encourage urethral
atonicity (diazepam 0.25 mg q12 and prazosin 0.13 mg q12). Oral acepromazine (0.1 mg)
was administered as a rescue sedative and antispasmodic.
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The patient represented to CUHA Emergency 15 months after initial presentation
after the owner noticed severe signs of intermittent stranguria for approximately 3 days.
That evening the stranguria had progressed to anuria that was unresponsive to
pharmacologic intervention. The ferret was otherwise healthy, with no other past
pertinent medical history, and was eating and drinking normally according to the owners.
PHYSICAL EXAM & STABILIZATION: Upon presentation, the patient was bright
and alert, but uncomfortable. The vital parameters were all within normal limitsi
(temperature 101.3 F, pulse 200 beats per minute, and respiration 32 breaths per minute).
On physical exam, the abdomen was distended by a turgid, full bladder that could not be
manually expressed. There was a questionable mass near the region of the left kidney on
abdominal palpation and mild periodontal disease noted. The remainder of the physical
exam was unremarkable.
The patient was sedated (butorphanol 0.2 mg/kg IM and midazolam 0.5 mg/kg
IM) so a urinary catheter could be placed. Urethral catheter placement is challenging in
the male ferret due to the animal’s small size and J-shaped os penis. The urethral opening
lies on the ventral aspect just proximal to the tip of the penis within the groove of the os
penisii. Similar to a dog, the os penis can be used to help extrude the penis from the
prepuce. A 3.5fr red rubber catheter was lubricated and easily passed in a sterile fashion
yielding 40 ml of urine (normal daily urine output for a full bladder in ferrets is 26-28 ml)
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. Urine was saved for diagnostic testing, and the catheter was removed due to financial
constraints. A blood sample was obtained for point of care testing that was normal save a
very mild anemia (PCV 40%, TS 6.2, AZO 16-26, and Glu 114 mg/dL). Buprenorphine
(0.01 mg/kg q6) as well as fluids (LRS 30 ml/kg q12) were administered subcutaneously.
Maintenance fluid rates for ferrets have been based on those for cats at 50 to 70
mL/kg/diii. The patient ate well and rested comfortably throughout the night.
DIFFERENTIAL DIAGNOSES: The top differential diagnoses for the patient’s urinary
obstruction included urolithiasis, prostatomegaly, and urethral stricture. Lower on the
differential list was neoplasia, ruled down by the patient’s age, and an upper motor
neuron bladder secondary to a neuropathy, ruled down by a lack of any other clinical
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signs. Urolithiasis is the most common cause of urinary obstruction in ferrets and the
patient had a history of this disease. In male ferrets, the second most common cause of
urinary obstruction is compression of the urethra secondary to cystic prostatomegaly
resultant from chronic androgen stimulation secondary to adrenal diseaseiv, v.
DIAGNOSTIC FINDINGS: The morning following presentation, the patient was again
painful and anuric, posturing so frequently that tenesmus and secondary loose stool
accompanied. The patient was maintained on buprenorphine at 0.02 mg/kg SQ q8 and
diazepam up to 0.2 mg PO q12. The ferret was sedated and an abdominal ultrasound was
performed. Visualization of the urinary bladder revealed a normal thickness and
echogenicity of the wall, and was negative for masses, stones, or sediment. A portion of
the bladder was found caudal to the pelvis and was very dilated. The precise cause of
lower urinary obstruction was not determined but might be occurring in the urethra
downstream from the ischial arch or might be associated with caudally displaced urinary
bladder with abnormal narrow region or substantially dilated prostatic and pelvic urethra
and patent cystourethral junction. Ureteral jets were not found by color flow Doppler, so
the trigone of the bladder could not be identified. The extreme dilatation of the caudally
displaced bladder (approximately two times larger than the normally positioned cranial
bladder) pointed to a perineal hernia with bladder prolapse as the new top differential
diagnosis, however other causes like malformation, stricture, neuromuscular problems, or
dilation secondary to downstream urethral obstruction could not be ruled out.
Additional ultrasonographic findings included: moderate generalized
splenomegaly of nonspecific pathogenesis (hyperplasia, extramedullary hematopoiesis,
inflammation, diffuse neoplasia); possible bilateral mild adrenomegaly; and a minuscule
amount of peritoneal fluid likely secondary to inflammation. The prostate was imaged to
be normal. Therefore, despite adrenomegaly (likely correlating with the mass felt near the
region of the left kidney o abdominal palpation) possibly pointing to early adrenocortical
disease, that was not the cause of the urinary obstruction
Following ultrasound, another 3.5Fr red-rubber catheter was passed. A sample of
urine was obtained for urinalysis and sediment exam testing. This time the patient was
fitted with an indwelling catheter and closed urine collection system. Once the catheter is
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in place, butterfly tape strips were used to suture the catheter to the skin in the ventral
abdomen in multiple locations. The catheter was then taped to the base of the tail to
reduce tension at the sutured areas. A closed urinary collection device was created from a
sterile fluid drip set and empty fluid bag3, 4, vi. Lastly a full body wrap consisting of an
orthopedic tube stocking with openings for arms and legs reinforced with 2” Elasticon
was fashioned. The ferret had a history of chewing out his urinary catheters, which was
not only time consuming and costly to replace, but served as a source of potential foreign
body if ingested.
Urinalysis results were unremarkable. The sediment was negative for crystals,
casts, bacteria or white blood cells ruling out stones or infection as the source of urinary
obstruction. The increased red blood cells (20-100 phpf) and epithelial cells (many) were
consistent with repeated catheterization experienced by the patient
TREATMENT: Based on the high index of suspicion of perineal hernia, the soft tissue
surgery service was consulted. While a perineal hernia had never been described in the
literature, clinical signs of intermittent urinary obstruction experienced by the patient
could be attributed to the bladder getting periodically entrapped in the hernia. This has
been described in cats and dogs with perineal hernia. The patient was taken to surgery for
a cytopexy to replace and secure the bladder cranially and prevent further herniation and
subsequent obstruction. The patient was induced under general anesthesia and monitored
in a standard fashion.
Cystopexy: A standard ventral midline celiotomy was performed. Once inside the
abdomen the bladder was located and pulled cranially. The bladder was emptied via
external syringe from the urinary catheter. A stay suture with 4-0 PDS was placed at the
apex of the bladder. An approximately 1 cm diameter area of the right body wall in line
with the cranial fist third of the incision, and a similar sized area of the right dorsal base
of the bladder were excoriated with a scalpel blade. Three tags of suture were placed
connecting the body wall to the bladder (serosa and muscularis layers) then they were
cinched down and secured with a surgeons knot in a cranial to caudal fashion. The
bladder stay suture was removed. The body wall and muscularis was closed with 4-0 PDS
in a simple continuous pattern, and the skin was closed in an intradermal pattern. The
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urinary catheter was removed, the urethra was patent on manual expression of the
bladder, and the patient recovered from anesthesia without complicationvii.
The patient was started on anti-inflammatories and antibiotics postoperatively in addition
to continued analgesics (buprenorphine 0.02 mg/kg SQ q8, meloxicam 0.2 mg/kg SQ
q24, ampicillian sublactam 22 mg/kg SQ q8, diazepam PRN).
The morning after surgery the patient was dehydrated, painful and again
exhibiting signs of stranguria and tenesmus. A suspected reherniation was ruled out by a
repeat abdominal ultrasound which showed an intact pexy site characterized by
traditional tenting of the rectus abdominus muscle and visible suture loops. The patient
was relieved of urine with an emergency cystocentesis (yielding 44 ml). After consulting
the owner, additional diagnostics were elected in order to revise the diagnosis.
Contrast Cystography: The patient was again sedated and a catheter was placed
in the urinary bladder prior to this study. With the patient in right lateral position, contrast
material (10 ml iohexol-350) was injected into the catheter as the catheter was retracted.
The patient was then examined in dorsal recumbency. With the patient again in right
lateral, the urinary bladder was manually compressed. Upon manual expression, a
urethral stricture was appreciated just proximal to the start of the os penis, as determined
by a lack of contrast media in the penile urethra and subsequent extreme dilatation of the
pelvic urethra. Additionally, a small rent in the pelvic urethral was seen, likely secondary
to the previous “cystocenesis” which in actuality was a urethrocentesis.
DEFINITIVE DIAGNOSIS: Penile urethral stricture with severely dilitated pelvic
urethra and iatrogenic pelvic urethral tear.
Due to the fragility of the urethra and in an effort to prepare the patient for
another surgery, the ferret was outfitted with another indwelling urinary catheter and was
hospitalized with supportive care for the next 48 hours. The day of surgery, the patient
was induced under general anesthesia, a jugular catheter was placed and he was
monitored in a standard fashion.
Perineal Urethrostomy: The patient was placed in dorsal recumbency and
prepped using standard aseptic technique. A 1-2cm incision was made on midline over
the prescrotal region using a micro blade. Blunt dissection of the subcutaneous tissues
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was performed to allow visualization of the penis retractor muscle and the urethra.
Hemorrhage was controlled by electrocautery. The location of the urethra was confirmed
by palpation of a previously placed indwelling the urinary catheter (red rubber). A fresh
micro blade was used to incise the urethra, making an approximately 1cm incision
parallel to the skin incision. The urethral mucosa and the skin were opposed and sutured
in a simple continuous pattern using 6-0 PDS. Two lines of suture were used, one on
either side of the urethrostomy. Two simple interrupted sutures were placed at the very
cranial and caudal ends of the urethrostomy site. Additionally, two simple interrupted
sutures were placed on the right edge of the site to improve skin-to-mucosa apposition. A
catheter could easily be passed through the stoma proximally and distally. The urinary
catheter was removed and patency of the site was ensured by palpating and expressing
the bladder and visualizing urine coming out of the stomaviii, ix.
OUTCOME: The surgery was a success and only a mild urinary incontinence was noted.
The patient was monitored in the intensive care unit for 24 hours with supportive care of
intravenous fluids (Lactated Ringers Solution at 3ml/hr), buprenophine, meloxicam, and
ampicillin sublactam. The jugular catheter was removed and the patient was transitioned
to oral medications once eating and drinking well. He was discharged to the care of his
owners 5 days after initial presentation and sent home on the following medications:
meloxicam (0.2 ml PO SID x4 days), diazepam (0.1-0.2 ml q12 PRN),
trimethoprim/sulfamethoxine (15 mg/kg q12 PO x10 days), and tramadol (5 mg/kg 0.35
ml PO q12-24 PRN x7 days).
The patient continued to do well at home postoperatively after being weaned off
all his medications. Two weeks following discharge and the owner reported that all
urinary incontinence had resolved, there had been no episodes of stranguria, and his
energy level was improved. The patient was to return for a recheck and suture removal a
week later.
DISCUSSION: Cystine stones are rare in ferrets accounting for only 16% of uroliths
submitted for analysis. According to the Minnesota Urolith Center, out of 435 uroliths
(1992-2009), struvite was the most common at 67%. The etiology of cystine urolithiasis
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in ferrets is currently unknown, though anecdotal reports have linked it with nutrition,
particularly ferrets eating a cat-food only diet. A familial pattern of inheritance has not
been reported in ferrets, but genetic factors associated with the disease have been
determined in humans and certain dog breeds impairing the renal proximal tubules ability
to reabsorb cystinex.
Adrenocortical disease is the second most common endocrinopathy in domestic
ferrets (after insulinoma) with an estimate of 70% of the US pet ferret population affected
in 2003. It has no sex predilection and affects mainly middle-aged ferrets with a mean
age of onset of 4 years old.xi The high incidence is likely due to a genetic bottleneck from
a small founder population. Unlike Cushing’s Disease of dogs and cats, ferret adrenal
disease affects the zona reticularis and thus results in a hyperandrogenism marked by
increases in sex hormones.
The clinical signs, and subsequent diagnosis of ferret adrenal disease, are largely a
result of increased sex hormones. Retrospective analysis has shown that the most
common presenting complaints include progressive alopecia (>90%) with accompanying
pruritis (40%), vulvar swelling (>70% of females) and cystic prostatic enlargement in
males—which may lead to emergency urinary obstruction, stranguria, or tenesmus. Other
clinical signs include mammary gland enlargement (both sexes), muscle wasting,
lethargy, aggression, and increased odor.7 In one study, estrogen was elevated in 36% of
cases, 7-hydoxyprogesterone was elevated in 60% of cases, and androstendione was
elevated n 76% of cases. 96% of ferrets with adrenocortical disease had an elevation in at
least one of the aforementioned hormones, and 22% showed an elevation in all three. xiiA
ferret sex steroid serum panel is available through the University of Tennessee that
validates increases in sex hormones (estrogen, 7-hydoxyprogesterone and
androstendione).xiii In male ferrets, an increase in one hormone is diagnostic. In female
ferrets, an increase in estrogen alone must be differentiated from other possible sources
including persistent ovarian remnant, but an increase in two or more is considered
diagnostic.
The patient ultimately had surgical success and the urinary obstruction was
relieved. However, one can not help to comment on the fact that if all imaging
diagnostics had been pursued prior to surgery, the patient could have been spared an
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unneccesary surgical procedure. While perineal hernia seemed likely based on
ultrasonographic evidence, it was a novel diagnosis not originally on the list of
differentials, and urethral stricture should have been ruled out first.
REFERENCES:
Wolf, TM. (2009). Ferrets. In: Manual of Exotic Pet Practice. St. Louis, MO: Elsevier
Saunders; 345-74.
i
Brown C & Polluck C. (2011).Urethral Catheterization of the Male Ferret for Treatment
of Urinary Tract Obstruction. Lab Animal Medicine 40 (1): 19-20.
ii
Castanheira deMatos, RE & Morrisey, JK. (2006). Common Procedures in the Pet
Ferret. The Veterinary Clinics of North America. Exotic Animal Practice. 9 (2): 346-65.
iii
Orcutt, CJ. (2003). Ferret Urogenital Diseases. The Veterinary Clinics of North
America. Exotic Animal Practice. 6 (1): 113-38.
iv
Fisher, PG. (2006). Exotic Mammal Renal Disease: Diagnosis and Treatment. The
Veterinary Clinics of North America. Exotic Animal Practice. 9 (1): 69-96.
v
Pollock, C. (2007). Emergency Medicine of the Ferret. The Veterinary Clinics of North
America. Exotic Animal Practice. 10 (2): 463-500.
vi
Mullen, HS & Beeber, NL. (2000). Miscellaneous Surgeries in Ferrets. The Veterinary
Clinics of North America. Exotic Animal Practice. 3 (3): 663-71.
vii
viii Bartlett,
LW. (2002). Ferret Soft Tissue Surgery. Seminars in Avian and Exotic Pet
Medicine.11 (4): 221-230
Lightfoot, T et al. (2012). Soft Tissue Surgery. In: Ferrets, Rabbits and Rodents,
Clinical Medicine and Surgery. 3rd ed. St. Louis, MO: Elsevier Saunders; 141-56.
ix
x
Nwaokone EE et al. (2013). Epidemiological Evaluation of Cystine Urolithiasis in
Domestic Ferrets (Mustela putorius furo): Seventy Cases (1992-2009). J Am Vet Med
Assoc. 242 (8): 1099-103.
Simone-Freilicher E. (2008). Adrenal Gland Disease in Ferrets. Vet Clin Exot Anim
11: 125-137
xii Rosenthal KL, Peterson ME. (1996). Evaluation of Plasma Androgen and Estrogen
Concentrations in Ferrets with Hyperadrenocorticism. J Am Vet Med Assoc 209:10971102.
xi
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The University of Tennesse Clinical Endrocrinology Service website. Date accessed:
2/15/2014. http://www.vet.utk.edu/diagnostic/endocrinology/
xiii
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