Ch 117 - Urethra Flashcards
List the layers of the urethra
- Mucosa
- Submucosa
- Muscularis
Describe the urethra muscularis in the male and female dogs and cat
Male dog:
- Inner longitudinal smooth surrounded by outer circumferential striated
- Smooth muscle is in the distal 2/3rds of the urethra
- Striated mostly Type II fast twitch, some Type I slow twitch
Male cats:
- 3 layers of smooth muscle - inner longitudinal, middle circumferential, outer longitudinal
Female dog:
- Three smooth muscle layers as male cats
- Smooth muscle essentially absent in terminal urethra
- Prominent sphincter of striated muscle at external urethral orifice
Female cat:
- Significantly more smooth muscle and significantly less striated urethral sphincter than female dog
What is the urethral diameter of male cats at the level of the bulbourethral glands compared to the penile urethra
- Bulbourethral gland 1.3mm
- Penile urethra 0.7mm
What is the theorised mechanism of hypothermia in cats with urethral obstruction?
- Reduction in the thermoregulatory set point in the hypothalamus secondary to uraemia
- Or secondary to volume depletion and shock
What is the time frame for renal decompensation and death in aminals with complete urethral obstruction?
- Renal decompensation within 24hr
- Death 3-6d
What fluid is most efficient for correcting electrolyte derangement with urethral obstruction?
LRS
List options and mode of action of each option for the treatment of hyperkalaemia
10% Ca Gluconate
- Increases threshold for cardiac myocyte depolarisation. 0.5-1.5ml/kg IV over 5-10 min, last 30-60min
IV dextrose +/- regular insulin
- Drived K intracellularly by cotransport. Lasts 2-4hr
Na Bicarb
- Enables H ions to move extracellularly in exchange for K. Only used if severe acidosis
List the critical factors which effect urethral healing
- Mucosal continuity
- Urine extravasation
If a strip of mucosa is left intact and urine is diverted, the urethral mucosa can regenerate within 7 days
How much narrowing of the urethral lumen occurs before clinical signs occur?
60%
List the options for a urethrostomy
- Scrotal
- Perineal
- Transpelvic
- Subpubic
- Prepubic
How long should the incision in the urethra be for a urethrostomy?
How much contraction is expected during healing?
- 2.5-4cm long (approx 5-8x urethral diameter)
- Will contract by 1/3-1/2 during healing
Hows does a continuous suture in a scrotal urethrostomy effect post-op haemorrhage?
- Decreases time of active haemorrhage from 4.2d to 0.2d
What is the name of the standard cat PU technique?
Wilson and Harrison technique
What ventral structures need to be transected during a cat PU?
- Ventral penile ligament
- Attachment of ischiocavernosus muscles
To what level is the penis freed and the urethra incised in a cat PU?
To the bulbourethral glands
What is the expected outcome after PU surgery?
- 12.8-25% early complications (haemorrhage, stricture, extravasation)
- Long-term complications 28% (UTI, recurrent FLUTD)
- Good long term outcome but most will require ongoing management of underlying uropathy
What muscles are elevated in the approach for a transpelvic urethrostomy?
- Gracilis
- External obturator
What muscles require elevation in the approach for a subpubic urethrostomy?
- Gracilis
- Adductor
Which urethrostomy has the highest rate or morbidity and complications?
Prepubic
- 6/16 cats incontinent
- Significant peristomal skin irritation
- Stricture, kinking or compression or urethra
List options for reinforcement of a tenuous urethral anastomosis
- Rectus abdominus flap
- Internal obturator flap
- Omentum
What is the prognosis after urethral resection and anastomosis?
- Guarded - Some degree of stenosis is expected
What is the most important factor in minimising stenosis after a urethral anastomosis?
Urinary diversion - either via u-cath or tube cystostomy
What is hypospadia? What breed is overrepresented?
- Failure of the fusion of the urogenital folds resulting in incomplete formation of the penile urethra
- Bostron Terriers overrepresented
What is epispadia?
What condition is often seen concurrently?
Failure of fusion of the dorsal penile urethra.
- May occur with concurrent bladder exstrophy (portions of bladder and abdominal wall absent and bladder appears inside-out)
List the 2 broad types of urethral fistulas
- Urethrorectal
- Urethrocutaneous
List the surgical options for a double urethra (urethral duplication)
- Open surgical removal
- Cyanoacrylate and coil embolisation
What % of bladder and urethral tumours are malignant in dogs and cats?
- 97%
What is the reported incontinence rate of dogs and cats after urethral stenting?
- 26% dogs
- 50% cats
List causes of urethral stricture
- Trauma
- Obstruction
- Inflammation
- Malignancy
- Iatrogenic surgical
List the treatment options for a urethral stricture
- Urethrostomy
- Resection and anastomosis
- Balloon dilatation
- Stent
- Urethral replacement (Aortic stent graft, Rectus abdominus axial pattern flap, ileal segment, oral mucosal grafts +/- adipose-derived stem cells and polyglycolic acid scaffold)
What breed are overrepresented for urethral prolapse?
What are the surgical options?
Recurrence rate?
English Bulldogs
Sx Options:
- Reduction and purse-string
- Urethropexy
- Resection and anastomosis
Long-term recurrence 57%
What can cause benign mass-like lesions within the urethra?
- Proliferative urethritis
- Fibroepithelial polyps
