Micturition Disorders Flashcards
Normal ureteral anatomy/structure
fibromuscular tubes, the wall is composed of outer adventitial layer, muscular layer, submucosa and mucosa of transitional epithelial cells
Muscular wall consists of 3 layers: outer longitudinal, middle circular and inner longitudinal everywhere except at the ureterovesicular junction (UVJ) where only longitudinal fibres are present
Prevention of retrograde urine flow in ureters
Tunnel into serosa obliquely
oblique path → valve like effect preventing retrograde urine flow from the bladder (combined with ureteral peristalsis and compliant bladder)
Control of ureteral peristalsis
Ureteral contraction occurs when urine enters the ureter → electrical impulses conducted b/w smooth muscle cells.
Alpha-1 AdrR are responsible for neurogenically mediated ureteral contraction
B receptors are involved in relaxation
Pathophysiology leading to renal injury in ureteral obstruction
increased Bowmans capsule pressure → reduced GFR and reduced renal blood flow as a result
→ continued elevated ureteral pressure further reduces renal blood flow
→ ischemic intrinsic kidney injury → nephron loss and fibrosis/scarring of kidney from intrarenal hypertension
Early intervention to alleviate obstruction seems critical to maximize recovery of renal function (4d in dogs with experimental ureteral ligation, probably starting with a healthy kidney)
DDx for ureteral obstructions
ureterolith, blood clot, stricture/stenosis, oedema, inflammation, intra/extramural neoplasia, circumcaval ureter, retroperitoneal fibrosis, bladder neoplasia invasion of distal ureter (primary ureteral neoplasia is rare), ureteral trauma.
Risk factors for feline ureteral obstruction studies
JFMS 2022 - case control study of risk factors for ureteral obstruction identified diet as the only significant factor - predominantly dry food diet associated with 16x increased risk of UO (combination diet vs wet food only not associated with difference in risk)
JVIM 2023 UK risk factors in cats - Vetcompass study did not look at diet. Females and >4y associated with increased risk as was British SH, Burmese and Persian
Medical management of ureteral obstruction - Tx used and recent article in cats
Medical dissolution/expulsion:IVFT (judicious to avoid overload), alpha antagonists (prazosin, tamsulosin), analgesia, amitriptyline (smooth muscle relaxant), some advocate use of steroids to reduce inflammation
In humans CCB and alpha antagonist have most evidence, amitriptyline not recommended.
Use extracorporeal dialysis to mediate effects of uraemia/electrolyte derangements while giving medical expulsion chance to work. NB dialysis in this case will not slow the progression of renal injury which is pressure induced
Percutaneous nephrostomy tube placement - to alleviate pressure while waiting for passage
DOGS - can attempt medical dissolution of nephrolith if struvite suspected but ONLY if not obstructive (as otherwise will not be bathed in appropriate urine for dissolution)
Spontaneous passage thought more likely to occur in dogs due to their wider ureter
If attempting dissolution of struvite ureterolith need to alleviate obstruction with stent to allow adequate access of ABx and urine.
CATS - most are Ca-ox ureteroliths so dissolution not possible. Other causes may have improved expulsion outcome (prev reported as 8-13%
Spontaneous passage may result in subsequent ureteral stricture
JVIM 2023 - outcome of BUO various Dx including strictures, various Tx overall success 30% - 50% if pyonephrosis, 23% of ureterolithiasis
Dimensions of renal pelvis/ureter not assoc with outcome, but size of urolith and proximal location were negative prognostic factors..
Surgical/intervention Tx options for ureteral obstructions - preferred methods of dogs vs cats
Ureteral stents:
More often reserved for use in dogs as can be placed cystoscopically.
JAVMA 2018 - 44 stent placement, only one death post-op. 26% developed UTI after stenting (present in 55% prior to stenting
Preferred over SUB in this species due to less invasive placement technique.
Recently used in Tx of 14 dogs with pyonephrosis.
Also preferred method for dogs with extramural malignant obstruction.
Largest study is 69 cats, require open approach in cats, 95% success rate for various causes of obstruction, 20% reobstruction, 37% dysuria
SUB:
DOGS - perioperative mortality 6%, possibly higher rate of infectious cause of ureteral obstruction so stents are preferred as first line compared to SUB.
CATS - perioperative mortality 6-21%.
Reported MST range from 280->800d. Likely v dependent on individual case factors, esp underlying CKD
Post-op complication rate as high as 40-80% reported usually after d/c, requires life-long management and regular SUB flush.
Shock wave lithotripsy (dogs only, nephrolith > ureterolith)
Endoscopic nephrolithotomy - get scope into renal pelvis then use direct lithotripsy laser.
Open Sx: ureterotomy, neoureterocystostomy, ureteronephrectomy.
Recent publications on feline SUB
JFMS 2022 - 37 cat retrospective study. No pre-op findings were found to be predictive of long term sCr.
JSAP 2021 - MST of 530d - length of survival significantly assoc with sCr at presentation
30 required revision surgery mostly for infection or kinking
JFMS 2021 - MST 274d in 24 cats (smaller study), 33% SUB obstruction post-op, 21% pyelonephritis
JVIM 2021 - 81 cats with BUO, 6% periop mortality, 26% infection rate, kink 10%. MST 821 days
JFMS 2021 - pre-op positive culture significantly assoc with development of post-op infection within 6 months in 118 cats
E.coli culture at any point was assoc with increased likelihood of implant removal or replacement.
JVIM 2019 - post-op ABX reduced risk of positive urine culture in cats prior to d/c
JAVMA 2018 - 174 SUB cases, 94% survive to d/c, high iCa assoc with increased risk of SUB obstruction
Difference in male and female dog urethral muscle
In the female dog, the bladder neck is augmented by a smooth muscle sphincter which encircles the cranial half of the urethra and gradually becomes incorporated with the striated muscle caudal to the vagina.
–> predominant constituents of the female urethra are collagenous and elastic fibres, smooth muscle is distributed uniformly
–> striated muscle at the external urethral orifice
Regardless of neuter status,female dogs have a higher proportion of collagen and lower proportion of muscle relative to males
Males have weak smooth muscle sphincter and is only present cranial to the prostate
The external striated muscle in the membranous urethra comprises >50% to 70% of the urethral wall along the length of the urethra; its circular orientation indicates sphincteric function
Storage phase of micturition (detrusor and local urethral reflex arc)
Detrusor stretch receptors –> pelvic n
–> reflex arc that increases urethral tone via enhanced by sympathetic innervation from caudal mesenteric ganglion (hypogastric nn) –> activation a1 adrenergic activation in intern smooth muscle sphincter and detrusor relaxation via B3 receptors
–> facilitates storage of urine
–> efferents from brain activate S1-3 pudendal nerve and somatic innervation of ext urethral sphincter (via ACh R) = local urethral reflex arc
Normal voiding micturition reflexes
stretch receptors in the detrusor muscle→ sensory fibres in the pelvic and hypogastric n. → pontine nuclear formation (micturition centre, integrates all other inputs on micturition)
–> activates descending UMN that inhibit somatic innervation of ext urethral sphincter (via pelvic nerve parasympathetic)
–> also innervates bladder wall and causes detrusor contraction via muscarinic ACh receptors
Also inhibitory signals to sympathetic innervation of bladder
Location of injury and symptoms of UMN bladder
Injury cranial to sacrum (ie not affecting somatic or parasympathetic input to bladder/urethra)
–> neurogenic functional obstruction as no parasympathetic inhibition to relax urethra (no pudendal or pelvic nerve function
Difficult to express bladder with reduced bladder tone.
Location of injury and symptoms of LMN bladder
S1-S3 spinal lesion
removes
Loss of somatic tone to external sphincter and unable to initiate normal micturition but leaks urine if any abdominal pressure applied
How to differentiate disorder of storage from voiding disorder in incontinence
If voluntary control of voiding is present the detrusor reflex is most likely intact. This also implies that urine can be held for a reasonable length of time. Disorders of storage present as involuntary leakage but the dog retains the ability to void normally
Increased PVRV could signify a disorder in voiding whereas normal PVRV with UI suggests a urine storage disorder
Palpate bladder before and after urination, if incompletely emptied more likely voiding disorder (also more likely have stranguria passing small amounts frequently)
PVRV of 0.2 to 1.0 mL/ kg can be considered normal for dogs, a PVRV >3 mL/kg is abnormal and signifies urine retention
Voiding disorders then subcategorised into mechanical and functional causes.
A history of posturing with a weak, interrupted stream toward the end of urination and increased PVRV is characteristic of FOO.
Often still can produce some form of urine stream
Stranguria with a weak or no urine stream may indicate complete obstruction, more com-monly caused by MOO
Ensure PUPD has been excluded as a cause of overflow incontinence
Perform neuro exam to r/o UMN bladder causing voiding disorder
