Ch 114 Kidneys Flashcards
Gross Anatomy
- cranial pole of the right kidney lies in the renal fossa of the caudate liver lobe
- Nerves, vesses, lymphatic and ureter enter at the hilus
- Outermost, there is a thin, fibrous capsule covering the kidney
- renal cortex is composed of glomeruli and adjacent structures
- The medulla is striated in appearance and projects into the renal pelvis
kidney functions
- removal of metabolic waste products
- maintenance of normal fluid balance
- regulation of blood pressure
How often are multiple renal arteries reportedly found?
In which kidney is this most common?
- 13% of dog kidneys
- 10% cat kidneys
- Left kidney is more common
Right kidney more commonly has multiple renal veins
Where do the capsular arteries commonly arise from?
Phrenicoabdominal and adrenal arteries
What is the role of the vasa recta capillaries?
- Extend from the cortec into the medulla, reabsorbing water from the collecting ducts and returning it back to systemic circulation
- Help to maintain hypertonicity of the renal medulla through countercurrent exchange system
Physiology
- basic functional unit of the kidney is the nephron
- the glomerulus is a tuft of capillaries enclosed within the glomerular capsule.
- glomerulus of a juxtamedullary nephron is located deep in the cortex near the corticomedullary junction. The thin limb of the loop of Henle extends deep into the inner medulla.
example functions:
- glomerulus filters blood
- proximal tubule bulk reabsorption or water and solutes
- regulation of acid, HCO3, Ca, Na, K
- juxtaglomerula appartus regulate GFR and BP
What structure helps to maintain renal autoregulation of blood flow?
Macula densa (between glomerulus and afferent arterioles)
What cells within the glomerulus are responsible for filtration?
- Podocytes - water and small particles under 60,000 daltons can freely pass through the filtration slits (Most cellular components of blood exceed this size)
- Inherent negative charge of the glomerulus basement also enhances the selective nature of filtration
What is normal urine production?
20-45ml/kg/d
What is the osmolality of the glomerular filtrate and of the medullary interstitial fluid?
Glomerular filtrate - 300mOs/L
Medullary interstitial fluid - 1200-1400mOs/L
What is normal renal blood flow?
- Approx 25% of CO
- 4ml/min/g of renal tissue
RBF
- Calculated as renal perfusion (systemic BP)/renal vascular resistance
- Vasoconstriction and vasodilation of the afferent and efferent renal arterioles are primarily responsible for renal vascular resistance.
- These vessels are therefore the targets for renal autoregulation.
- Autoregulation allows adequate blood flow during times of systemic hypotension or hypertension
- diseased kidney has decreased autoregulatory ability > susceptible to ischemic injury during times of hypotension
How does GFR relate to blood flow?
GFR is roughly 20% of renal plasma flow
What determines the concentrating ability of the kidney?
Based on renal medullary hyperosmolarity which is maintained by the vasa recta through a counter-current mechanism
Because of increased osmolarity of blood leaving the renal medulla, particles such as urea transfer from blood exiting the medulla into blood entering the medulla. This countercurrent exchange permits the medullary interstitium surrounding the collecting ducts to maintain a high osmolarity.
What can cause decreased concentrating ability of the kidney?
Increased blood flow through the vasa recta
- Vasodilation
- Increased arterial pressure
- Increased fluid volume
What mechanisms create medullary interstitial hyperosmolarity?
- Faculative diffusion of large molecules (urea) into the interstitium
- Limited ability of water to diffuse into interstitium
- Active transport of Na, K, Cl and other electrolytes into the interstitium from the thick portion of the proximal loop of Henle
Urea contributes 40-50%. Absorbed in the collecting ducts UT-A1, stimulated by ADH. It is then recycles by moving to thin limb of Loop of Henle
Healing of the Upper Urinary Tract
- Inflammation and infarction occur with parenchymal ischemia secondary to compression, electrocoagulation, vascular transection, or inflammation and delay wound healing
- Horizontal mattress suture > parenchymal necrosis, fibrosis, scarring and atrophy
diagnostics
- Thoracic radiographs should be performed in any animal in which neoplasia is suspected
- normal canine kidney is 2.0 to 2.5 times the length of the adjacent vertebra
- normal feline kidney length is 2 to 3 times the adjacent vertebrae
excretory urogram or intravenous pyelogram
- contrast is removed by passive glomerular filtration and is therefore a function, but not a measurement, of glomerular filtration rate (GFR)
- contrast toxicity: exact mechanism of renal toxicity is not well understood. Systemic administration of contrast agents may result in hypotension
- RADS: 5, 20, and 40 minutes after injection
- 400 mg/kg
- 1st = renal angiographic phase, demonstrates the arterial supply of the kidney
- 2nd = renal phase, “blush” throughout the parenchyma.
- 3rd = excretory phase, contrast flows into the collecting ducts and transported into pelvis
Pyelography
- direct injection into the renal pelvis
- concern about giving a systemic dose of contrast or when the renal artery is obstructed
Ultrasound
- Major ultrasound findings in affected dogs included renal pelvic dilatation (usually with proximal ureteral dilatation)
- noninvasively evaluating renal structure
- Doppler ultrasonic imaging can be used to determine the resistance index of the kidney
CT
- accurately predict renal vasculature anatomy and is thought to be superior to excretory urography for evaluation of renal vasculature in potential kidney donors.
- Dynamic CT has been used to estimate glomerular filtration rate
List some indications for renal surgery
- Unresponsive pyelonephritis
- Perinephric abscess or cyst
- Unilateral renal neoplasia
- Severe renal trauma
- Ureteral consitions causing severe irresolvable hydronephrosis
What factors increase the risk of haemorrhage during renal surgery?
Hypertension
Thrombocytopaenia
Azotaemia - inhibits platelet adhesion and aggregation. Should perform BMBT
What is the rate of pulmonary metastasis with primary renal neoplasia?
Dog: 16-48%
Cat: 43%
Which lateral radiographs is better for viewing both kidneys?
What is the normal kidney size?
Right lateral
Dogs: 2-2.5x length of adjacent vertebra
Cats: 2-3x length of adjacent vertebra
What imaging modality of best for determining the GFR (and therefore function) of the kidneys?
- Nuclear scintigraphy
- Plasma clearance tests are more accurate but more difficult to perform and time consuming
- Inherent renal autoregulatory mechanisms can result in substantial variation in glomerular filtration rate of normal animals
What radiopharmaceuticals can be used for scintigraphy of the kidney?
Technitium 99m - DTPA (diethylenetriaminepentaacetic acid)
Technetium 99m - MAG3 (mercaptoacetyltriglycine) - better for patients with very limited renal function and for performing renal perfusion studies to evaluate transplant patients
pre-op consdierations
- uremia, blood pressure irregularities, anemia, coagulopathies, and electrolyte imbalances
- urinary catheter is placed to monitor urine production
- Maintenance of renal perfusion under anesthesia is critical
- Drugs that cause hypotension (e.g., acepromazine) or nephrotoxicity (e.g., aminoglycosides or nonsteroidal antiinflammatory drugs) should be avoided
- Dopamine or dobutamine may be required intraoperatively in hypotensive
- Epidural administration can reduce intraoperative anesthetic
- nephrectomy, ideally functional test of contralateral kidney
list developmental anaomolies
- Renal agenesis
- renal dysplasia
- renal ectopia
- fised kidney
- Polyctstic Kidney disease
Where is the most common location of renal ectopia?
Pelvis
What breeds are predisposed to polycystic kidney disease?
Persians (37-38% of breed)
Bull Terriers
What breeds are overrepresented with renal calculi?
What is the most common calculi?
List potential causes of renal calculi
- Siamese cats, Bichon Frise
- Calcium oxalate
Oversaturation of the urine with calculogenic substances
- Organ dysfunction (liver dz)
- neoplasia (hyperCa2+)
- Increased Ca intake
- Drugs
- Increased intestinal absorption
- Impaired renal reabsorption
- Excessive skeletal mobilisation
List options for stone removal
cannot be dissolved with medical protocols
- Extracorporeal shockwave lithotripsy
- Nephrotomy
- Pyelolithotomy
- Endoscopic nephrolithotomy (intracorporeal lithotripsy)
- nephrectomy (with a unilateral severely hydronephrotic, infected, or nonfunctional)
cats with mild to moderate renal disease, the presence of renal calculi was not associated with progression of renal disease or a difference in mortality rates from renal disease - sx may not be needed
What are the most common renal neoplasias in cats and dogs?
Cats: Lymphoma (can frequently be diagnosed with fine needle aspiration.)
Dogs: Carcinoma
hematuria, weight loss, lethargy, inappetence, abdominal mass
ddx neoplasia
transitional cell carcinoma
transitional cell papilloma
anaplastic sarcomas and carcinomas,
hemangiosarcoma,
lymphoma,
nephroblastoma
angiomyxoma.
What inherited neoplastic condition of the kidneys can effect young GSD?
Renal cystadenocarcinoma with nodular dermatofibrosis
- Bilateral multifocal renal tumours
- Firm nodules of dense collagen in the skin and SQ
- Females commonly also have uterine leiomyoma
- Mutation of FLCN gene, affecting folliculin (a potentially tumour suppressing portein)
- 50% mets
List paraneoplastic syndromes which can be seen with renal neoplasis
Polycythaemia and thrombocytosis in cats
HyperCa
Hypoglycaemia
Leucocytosis
Peripheral neuropathy
What is the rate of bilateral renal neoplasia?
4-32%
Neoplasia Sx
- Unilateral nephrectomy
- humans: (partial nephrectomy) > nephron-sparing procedures helps to prevent development of anuria
What is the MST for renal neoplasia?
Carcinoma - 16m
Sarcoma - 9m
Nephroblastoma - 6m
HSA - 278d (haemoperitoneum has significantly shorter survival 62d
ist some DDx of abnormal appearance of the kidney
Developmental abnormalities
Calculi
Neoplasia
Acquired renal cyst
Perirenal pseudocyst
Renal abscess
Trauma
Kidney worms (Dioctophyma renale)
Acquired Renal Cysts
- secondary to chronic nephropathies or may be incidental findings in healthy dog
- All affected dogs had systemic hypertension
- Cysts were drained percutaneously in anesthetized dogs > 95% ethanol instilled then removed
List some treatment options for severe renal trauma?
- Ureteronephrectomy
- Wrap in semielastic polyglactin mesh
- Wrap in polyglycolic acid mesh
- Sterile, nonabsorbable cyanoacrylate for small lacerations
When comparing mesh to partial nephrecomy, creatinine clearance ratio was 0.93 for mesh and 0.58 for partial nephrectomy
Idiopathic Renal Hematuria
- Affected dogs are often large breed and less than 2 years of age.
- Accumulation of blood clots in the bladder or ureters may result in obstruction and secondary hydronephrosis/hydroureter.
- 30% have or will develop bilateral disease.
- Diagnosis is best performed via cystoscopy.
- Local sclerotherapy (better than kidney removal)
List some contraindications for renal biopsy
What needle can be used?
Contraindications:
- Uncontrolled coagulopathy
- Hypertension
- Large or multiple renal cysts or abscesses
- Extensive pyelonephritis
- Ureteral obstruction
- Severe hydronephrosis
Monopty biopsy needle
sufficient size so can be submitted for transmission electron microscopy
list methods of renal biopsy
- percutaenous
- ultrasound guisded
- keyhole
- laparscopic
- incisional biopsy (closed with simple interrupted or cruciate sutures of 3-0 or 4-0 absorbable, consdier arterial occlusion for <20min)
What is the complication rate of surgical renal biopsy?
What factors have been associated with increased complications?
- Complications 1-21.7% (Major in 8.9%, haemorrhage most common)
- Mortality rate less then 3%
Factors associated with complications: - Thrombocytopaenia
- Prolonged clotting times
- Creatinine above 5mg/dL
- Patient older than 4yo
- BW less than 5kg
- hypertension
haematoma, cyst, hydronephrosis, fibrosis)
List some indications for nephrotomy
Biopsy
Removal of nephroliths or other obstructive lesions
Chronic infection
Persistent haematuria of renal origin
Persistent hydronephrosis
What are the 2 options for nephrotomy?
- Bisectional nephrotomy (sharp dissection of the renal parenchyma)
- Intersegmental nephrotomy (Blunt dissection)
Bisectional recommended - faster, easier, no difference in post-op GFR between the 2 techniques
Inconsistent findings regarding the effect of nephrotomy on renal function serve to remind the surgeon that numerous factors may affect renal function after surgical incision.
temporary occlusion of vessels, better control over intraop hemorrhage.
What should be the maximum occlusion time of the renal vessels?
20min
How do you close a partial nephrectomy?
indications?
- Overlapping mattress sutures through the parenchyma and apposition of the overlying capsule
- If cannot be apposed, can tack omentum to exposed surface
- Nephron-sparing surgery may be a more appropriate option for animals that have a reduced glomerular filtration rate in their remaining kidney
List potential complications following a partial nephrectomy
Haemorrhage
Urine leakage
Urine fistula
What is the expected orientation of the renal vessels?
When in normal orientation, renal vein is ventral to renal artery
When the kidney is rotated ventromedially, renal artery is lateral to renal vein
Nephrectomy and Ureteronephrectomy
- If possible, function of the kidney to be left in the patient should be evaluated with scintigraphy
- Failure to accurately identify an early branch or a double renal artery can result in significant hemorrhage
- leaving the smallest ureteral remnant possible.
- concerned that a distal ureteral remnant permits urine reflux with resultant persistence or development of urinary tract infectio
How many ports are required for a laparoscopic nephrectomy?
3 to 4 port technique (1 caudal to umbilicus, 1 caudal to last rib and 1 cranial to pelvic limb for triangulation)
Complications associated with nephrectomy
- progression of preexisting kidney disease,
- acute renal failure,
- failure to resolve underlying clinical signs,
- inadvertent damage to other abdominal organs
Nephrostomy Tube Placement
Nephrostomy catheter placement is used to stabilize patients
- Earlier use of Foley, red rubber, or latex catheters led to high complication rates, including urine leakage, infection, and hemorrhage.
- A retrospective study reported complications in 46% of cats, with urine leakage being the most common issue.
- More recent studies using locking-loop pigtail nephrostomy catheters showed fewer complications (10%), such as subcutaneous urine leakage and accidental dislodgment.
- Renal function improved in most patients who survived 72 hours post-surgery.
- Catheters were typically removed after a median of 7 days, with longer durations (21 days) in cases without concurrent nephropexy.
Unilateral nephrectomy in dogs is associated with a high rate of intraoperative and postoperative complications
Carley Johnson 2024
69 dogs. retorspective
Complications occurred in 44.9% and 42.6% of dogs in the intraoperative and postoperative periods
Most of these were lower-grade,
7 dogs died during the postoperative period.
An acute kidney injury was diagnosed in 12 dogs postoperatively, with 2 dogs euthanized due to the severity of the injury. (17%)
Chronic kidney disease was diagnosed in almost 50% of the population with available long-term follow-up. (and 50% of these were euthnased for this reasons)
Glomerular filtration rate was assessed in 9 (13%) dogs, with only 2 (16.7%) dogs having abnormal GFR of their contralateral kidney. Dogs were presented primarily for unilateral nephrectomy for treatment of neoplastic renal lesions (n = 37), benign lesions (30),
Unilateral nephrectomy has been reported to cause postoperative AKI in approximately 21% to 34% of human patients.
suspected that these animals may be more susceptible to CKD due to the reduction of functional nephrons.
Transarterial chemoembolisation
for palliative treatment of renal cell
carcinoma in two dogs with pulmonary
metastasis
A. Kimata 2022
postoperative radiographs demonstrated a decrease in the tumour size. The dogs
died 215 and 525 days after the initial evaluation, respectively. As a palliative treatment
Upper urolithiasis in cats with
chronic kidney disease: prevalence
and investigation of serum and
urinary calcium concentrations
Huai-hsun Hsu 2022
Among the 140 cats with CKD, the prevalence of upper urolithiasis was 73%.
Cats with CKD that were purebred, fed dry food and fed urine-acidifying food only often
had upper urolithiasis
upper urolithiasis
itself may be a cause of CKD as obstruction of ureteroliths
or nephroliths can unknowingly damage the kidney
when occurring unilaterally
Diagnostic utility of renal fine-needle
aspirate cytology and ultrasound
in the cat
Camille A McAloney 2018
Of 96 cytologic submissions available for review, diagnostic yield was 68%
Of
12 confirmed cases, cytology was 100% sensitive and specific for the detection of neoplasia
Simple ectopic left kidney in the pelvic
cavity in a cat
In conclusion, based on current evidence, the WSAVA-GPC
supports the long-term administration of the lowest effective
doses of meloxicam and robenacoxib in cats with concomitant chronic pain and CKD as part of a multimodal approach that
includes non-pharmacological therapies,
not all cats are
satisfactory candidates for long-term NSAID therapy. Cats must
have stable CKD, and maintenance of proper hydration is paramount.
Stable CKD. For example, a stable patient with minimal changes
in bodyweight and creatinine over a period of at least 2 months
and controlled concurrent conditions including hypertension.
* The safety of NSAID therapy in cats with advanced CKD
remains unknown. Most available studies have reported long-term
NSAID therapy in IRIS stages 1 and 2 cats. Cats of IRIS
stage 3 have also been treated but less commonly
Endoscopic nephrolithotomy for the removal
of complicated nephroliths in dogs and cats:
16 kidneys in 12 patients (2005–2017)
Brian Petrovsky 2019
Indications for nephrolith removal included massive calculi displacing parenchyma
(n = 7), recurrent urinary tract infections (5), and ureteral outflow obstruction
(4).
Procedure-related complications included
renal puncture–associated hemorrhage requiring a blood transfusion (n = 1),
renal capsule tear (1), and ureteral puncture (1); all were managed without
adverse consequence. Five of 12 patients remained alive at the final follow-up
(median, 557 days after ENL), and none died from the procedure.
the decrease in GFR
associated with surgical nephrotomy is a major concern.
Endoscopic nephrolithotomy involves intracorporeal
lithotripsy with removal of stone fragments
through a renal-access sheath. results
in renal parenchymal dilation and spreading
of the nephrons, rather than transection, causing
minimal trauma.11,23
