Renal and Ureteral Abnormalities Flashcards
What is renal failure
loss of urine concentrating ability
polyuria is an early sign of renal failure
indicates > 66% functional loss of nephrons
urine SG <1.030 (dog); urine SG < 1.035 (cat)
persistent renal azotaemia ie high urea and creatinine AND relatively dilute urine (<1.035 in a cat; <1.030 in a dog)
indicates >75% functional loss of nephrons
both kidneys must be affected
high SDMA - may be an early marker of renal failure
indicates >25% functional loss of nephrons
What is chronic kidney disease
Presence of functional or structural changes in 1 or both kidneys for > 3 months
Clinically silent disease in the early stages (until 66-75% loss of nephrons)- no azotaemia
late diagnosis is inevitable
More common in older animals
30-50% of cats >15 years old have CKD
Stages of chronic kidney disease
Initially: destruction and loss of nephrons allows remaining nephrons to hypertrophy
Progressive and irreversible loss of nephrons:
rate of progression is very variable
cats usually survive longer than dogs- tend to have stable disease for longer
End stage: irrespective of the initial cause of damage the end result is fibrosis:
tubulointerstitial nephritis (common):
scar tissue replaces functional nephrons
histological description
cause usually unknown
What is acute kidney injury
Sudden onset damage which might be:
reversible
progressive with permanent loss of nephrons -> CKD
rapidly fatal due to overwhelming acute damage to kidneys shutting down urine production
a complication of pre existing CKD ie acute on chronic kidney disease
Early diagnosis is crucial to try to limit disease progression
Prevention of AKI is a priority when managing many critical care and emergency patients
!!!when to worry: increasing creatinine in a sick patient, ie. doesn’t even need to be “abnormal”!
Possible causes of AKI
Poor renal perfusion or cardiovascular disease or severe hypoxia:
critical care patients
emergency cases
Nephrotoxins…some examples:
ethylene glycol (anti freeze, more common in cats than dogs)
lily toxicity (cats only)
grape/raisin toxicity (dogs only)
vitamin D supplements/human psoriasis creams
NSAIDs can be nephrotoxic at high doses especially in dehydrated patients
Obstructive disease (calculi, blood clots, neoplasia)
urethral -> both kidneys affected
ureteric -> 1 kidney at a time (usually!)
Infection
localised infection in the renal pelvis (pyelonephritis)
systemic infection causing damage to the kidney (leptospirosis in dogs; FIP in cats)
renal abscess (large animals, very rare in small animals)
Hypercalcaemia
Cutaneous and renal glomerular vasculopathy (“Alabama rot” in dogs)
cause currently unknown
Possible Causes of CKD
Often no definitive diagnosis ie underlying cause of end stage renal disease not found
Consequence of any cause of AKI where renal damage doesn’t reverse but isn’t fatal
Familial renal disease such as…:
juvenile nephropathy in Boxer dogs
renal dysplasia in Shih Tzu, Lhasa Apso, Golden Retriever
amyloidosis especially in Sharpei; Abyssinian
polycystic kidney disease (cats)
breed specific (Persians and related breeds)
autosomal dominant trait
Inflammation/immune mediated disease -> glomerular damage:
glomerulonephritis (link to immune mediated disease teaching; type III HS causing immune complex disease in the glomerulus)
protein losing nephropathy
Ischaemia, renal infarcts, vascular injury
!!UNKNOWN- most likely for most cases of CKD!!
Usually we manage the consequences rather than treat the primary disease!
Examples of when we suspect renal disease had caused failure
young animal with familial renal disease?
old cat with increased likelihood of CKD?
any exposure to toxins?
any nephrotoxic drugs?
any other illness which might target the kidneys:
FIP, lymphoma in cats
lepto in dogs….causes hepatitis as well
post RTA or other situation where hypovolaemia -> ↓renal perfusion
3 features of normal ureters
Fibromuscular tubes carrying urine from renal pelvis to bladder neck (insertion site)
Peristaltic activity
Retroperitoneal structures
Congenital ureteric abnormalities
More common in dogs! rare in cats!
Ectopic ureter: abnormal site of insertion distally
Unilateral or bilateral
Clinical problems: F > M, can be asymptomatic
Incontinence
Urine scalding and dermatitis/pyoderma
UTI: lower UTI +/- ascending -> pyelonephritis
What is extra/intramural ectopic ureter
Extramural: inserts in urethra, vestibule or vagina (females) or ductus deferens (male)
Intramural: correct insertion site at trigone of bladder but tunnels in urethral wall to open distally
Traumatic injury to the ureter
rare but cats more likely than dogs
Complication of surgery: eg a spay if ureter is included in the ligature for the ovarian pedicle or the cervical stump
Avulsion or partial tear: eg as a result of RTA
Urine leak from ureter -> assess location with ultrasound:
retroperitoneal fluid if proximal injury
peritoneal fluid if distal injury close to bladder
Ureteral Obstruction
Intraluminal (lumen of ureter blocked) obstruction caused by:
calculi (esp calcium oxalate calculi in cats)
blood clots
inflammatory debris
Intramural (change in wall blocks ureter) obstruction caused by:
stricture (eg repair of damage from previous ureteric calculus that passed)
neoplasia (rare)
Extramural obstruction (eg post op complication with ligated ureter)
Unilateral Ureteral Obstruction
Easily missed because non-specific signs (pain)
↑ ureteric pressure proximal to obstruction => ↑ renal tubular pressure => ↓GFR
Complete obstruction => hydronephrosis => fibrosis (“small kidney”)
Compensatory hypertrophy of normal kidney can occur (“big kidney”)
Not azotaemic even if affected kidney shuts down as long as 2nd kidney healthy
What happens with a 2nd ureteral obstruction
Lightening can strike twice: big kidney/little kidney cats
Serious and life threatening because often relying on the big kidney only for adequate renal function (small kidney likely non functional or severely ↓ function)
If 2nd side obstructs => renal pain AND signs of azotaemia
AKI, therefore can be reversible with prompt diagnosis and treatment
Don’t miss these cats- they will need your help!
