Urinary path

What structures make up the lower urinary tract, and what are its two main functions?

Structures: ureters, urinary bladder, urethra
Functions:

1. Urination

2. Prevent pathogen entry (includes protective vesicoureteral valve)
   Most lower urinary disease results from disruption of one or both functions

What are the major causes of impaired urination and what downstream consequences occur?

Causes:

• Obstruction (most important; includes urolithiasis)

• Congenital/developmental anomalies:

  • Aplasia/agenesis

  • Hypoplasia

  • Ectopia → predisposed to ascending infection due to the angle of the ureters

• Inflammation

• Neoplasia

Consequences (upstream dilation):

• Hydrourethra

• Bladder distension or rupture (may also be neuroparalytic)

• Hydroureter

• Hydronephrosis

Which urolith types are common vs uncommon in major domestic species?

Dogs:

• Common: struvite, oxalate, purines (urate/uric acid, xanthine)

• Uncommon: silica, cystine, calcium phosphate

Cats:

• Common: struvite, oxalate

• Uncommon: urate, cystine

Cattle:

• Common: silica, struvite, carbonate

• Uncommon: xanthine

Sheep:

• Common: silica, struvite, oxalate, “clover stones,” carbonate

• Uncommon: xanthine

Horse:

• Common: carbonate

Pig:

• Common: urate

What factors predispose animals to urolith formation?

• High levels of calculogenic material in urine

• Urine pH (e.g., alkaline → struvite)

• Reduced water intake

• Infection → change micro environment

• Obstruction

• Structural abnormalities

• Foreign material (suture, bacteria, cells)

What new type of urolith has been recently recognized in dogs and what causes it?

Calcium tartrate tetrahydrate (CTT) uroliths, associated with diets containing:

• Fresh dog food and/or homemade diets

• Supplements containing choline bitartrate

stones…..

Where do urethral obstructions commonly occur in different species?

• Ruminants: ischial arch, sigmoid flexure, vermiform appendage in rams

• Dogs: proximal end of os penis

• Cats: anywhere along urethra
  Obstruction severity depends on anatomy and stone characteristics

What complications are shown in the necropsy images related to urinary obstruction?

• Marked hydronephrosis

• Hydroureter

• Severe bladder distention

• Consequences of prolonged obstruction → pressure atrophy and renal damage

Cystitis → What natural defense mechanisms protect the lower urinary tract from infection?

• Constant urine flow

• Intact urothelium

• Tamm-Horsfall mucoprotein

• IgA & IgG → prevents bacteria from adhering to surfaces

• Surface GAGs

• Urinary oligosaccharides

• Acidic urine (esp. dogs, cats) + high osmolality

• Urothelial exfoliation

• Phagocytosis by superficial urothelial cells

What factors predispose animals to cystitis?

• Urinary stasis

• Epithelial trauma:

  • Uroliths

  • Catheters

  • Chemicals (cyclophosphamide, bracken fern)

• Diabetes mellitus

• Cystocentesis

Which pathogens commonly cause cystitis, and what species-specific agents exist?

Ascending infections from rectal or cutaneous flora.
Common in all species:

• Uropathogenic E. coli

• Proteus vulgaris

• Streptococcus spp.

• Staphylococcus spp.

Species-specific:

• Cows: Corynebacterium renale group (C. renale, C. pilosum, C. cystitidis)

• Dogs: Corynebacterium urealyticum → encrusted cystitis → struvite

• Pigs: Actinobaculum suis

What gross features define acute hemorrhagic cystitis?

• Dark red discoloration

• Hemorrhage throughout mucosa

• Often associated with bacterial infection or toxic injury

What pathogen causes severe cystitis and pyelonephritis in pigs?

• Actinobaculum suis

• Causes ascending infection → cystitis → pyelonephritis

• Particularly severe in sows → due to estrus, hormonal component

What is lymphonodular cystitis and in what species is it common?

• Nodular mucosal lymphoid hyperplasia within the bladder wall → chronic

• Often incidental

• Seen in cattle

What is polypoid cystitis and what causes it?

• Reactive inflammatory polyps arising from chronic mucosal irritation from stones

• Usually due to chronic UTI or long-standing catheterization

• Can mimic bladder neoplasia grossly

What is emphysematous cystitis and what predisposes to it?

• Gas bubbles within the bladder wall → produced by gas-forming bacteria

• Seen with diabetes mellitus, glucosuria, chronic infection

• Grossly: emphysema in mucosa and submucosa

What does emphysematous cystitis look like grossly and what causes it?

• Gas accumulates in mucosa and submucosa of the bladder.

• Caused by gas-producing bacteria, often in diabetic animals with glucosuria → when give exogenous glucose/meds for milk fever

• Appears bubbly, crepitant, and raised under the mucosa

How common is LUT neoplasia and which species get it?

• LUT neoplasia is uncommon overall.

• Occurs mainly in cows, dogs, and cats

What type of bladder tumor is most common in dogs?

Transitional cell carcinoma (TCC) is the most common primary LUT tumor in dogs

• Often occurs at the trigone.

• Highly invasive and often malignant

What are the major forms of Urothelial cell carcinoma(TCC) and what is its behavior?

• Forms: Papillary, polypoid, sessile, or grossly inapparent (check prostate)

• Behavior: Locally invasive, malignant, can metastasize.

• Other possible LUT tumors: SCC, adenocarcinoma

• ~50% met → invasive and malignant

• will get squamous metaplasia

What proportion of Botryoid Rhabdomyosarcoma tumors are stromal and what is their behavior?

• Stromal tumors = <20% of LUT tumors.

• Usually benign.

• Fibrosarcomas can metastasize; leiomyosarcomas less commonly

• Young animals (<2 years)

• Large-breed dogs (esp. St. Bernards)

• Females > males (2:1)

• Often infiltrate the bladder wall and can metastasize; associated with hypertrophic osteopathy

What plant causes bovine enzootic hematuria and what lesions occur?

• Cause: Bracken fern (Pteridium aquilinum)

  

• Leads to:

  • Chronic hematuria

  • Mixed benign & malignant tumors (approx. 50%)

    • Papillomas

    • Fibromas

    • Hemangiomas

    • Carcinomas

    • Hemangiosarcomas

• Contains multiple carcinogens (ptaquiloside, quercetin)

• most often found on ventral bladder → urine pooling 

What percentage of cardiac output goes to the kidney?

• Approximately 25% of cardiac output.

• Kidney weight: ~0.5% of body weight

• 10% of oxygen consumption

What major structures are highlighted in the renal diagram?

• Cortex, medulla, pelvis

• Glomeruli concentrated in cortex

• Medulla receives blood mostly from juxtamedullary glomeruli to absorb water

What diseases are unique to the kidney (not LUT)?

• Hydronephrosis

• Renal anomalies

• Renal cysts

• Medullary necrosis

• Infarcts

• Renal neoplasia

What does hydronephrosis look like grossly?

• Dilated renal pelvis

• Thinned cortex

• Progressive pressure atrophy

• no room to expand due to the fixed cortex, fluid accumulates in the kidney. kidney does not have a shut off system and will continue producing urine

What is the pathophysiology of hydronephrosis?

• Capsule is non-expansile

• Obstruction → ↑ intrarenal pressure

• Lymphatics & veins obstruct → ↓ blood flow → hypoxia

• Results in pressure atrophy and apoptosis of renal cells

What defines juvenile nephropathy and what is the underlying pathology?

• Clinical diagnosis of congenital/hereditary renal disease.

• Features:

  • Uremia at young age (6–9 months or 4–18 months).

  • Often Type IV collagen defect in glomerular BM → hereditary nephropathy.

  • Membranoproliferative GN may occur.

  • Some cases involve tubular atrophy and interstitial fibrosis from unknown cause

What structures characterize renal dysplasia?

• Abnormal structures:

  • Blind-ended collecting ducts

  • Atypical tubular epithelium

  • Primitive ducts

• Inappropriate/immature structures:

  • Immature glomeruli

  • Undifferentiated mesenchyme (cortex/medulla)

• Possible osseous/cartilaginous metaplasia

• Often associated with ureteral anomalies → predisposed to pyelonephritis

• Related anomalies: hypoplasia, aplasia

What are the three main mechanisms of renal cyst formation?

1. Obstructive

2. Altered tubular basement membrane

3. Disordered growth of tubular epithelium with focal hyperplasia

Types:

• Simple renal cysts: all species, most common in cows/pigs

• Polycystic kidney disease (PKD):

  • ADPKD: Persians, Bull terriers, pigs, lambs

    • Bilateral cysts of convoluted tubules → renal failure

    • May have hepatic/pancreatic cysts

    • Mutation in PKD1

  • ARPKD: Cairns, Westies, sheep, Persians

    • Often with biliary cysts

  • CPKD: all domestic species

    • Stillbirths or neonatal death from renal failure

What gross features define Polycystic kidney disease?

• Numerous, variably sized cortical and medullary cysts

• Bilaterally enlarged kidneys

• Replacement of parenchyma with cystic spaces

What is medullary necrosis and what predisposes the medulla to injury?

• Medullary necrosis = necrosis of renal papilla/central medulla.

• Medulla is naturally hypoxic due to countercurrent blood supply

Why are cortical glomeruli more vulnerable to ischemia?

• Cortex = high flow, high demand

• Blood from most glomeruli supplies cortex directly

• Less redundancy compared to juxtamedullary glomeruli

How do NSAIDs lead to medullary (papillary) necrosis?

• Medulla relies on prostaglandins + nitric oxide for vasodilation.

• NSAIDs (COX-1 inhibitors) block prostaglandin production → loss of protection → ischemia.

• Necrotic papilla may slough and obstruct the ureter

What clinical signs are associated with acute papillary necrosis?

• Hematuria

• Proteinuria

• Casts

• Oliguria, then polyuria with poor concentrating ability

What determines the appearance and severity of renal infarcts?

• Depends on:

  • Cause: septic vs non-septic emboli

  • Vessel affected:

    • Renal artery

    • Interlobar artery

    • Arcuate artery

    • Interlobular artery

• Renal infarcts are common, but often clinically insignificant unless large or infected.

• Classic appearance: wedge-shaped, pale cortex with hyperemic rim

What are the most common types of renal tumors across species?

• Primary tumors are rare; metastasis more common

• Adenoma: rare (horse, cow)

• Carcinoma: #1 in cows, horses, dogs

• Nephroblastoma: #1 in pigs, chickens

What does renal carcinoma in the horse look like grossly?

• Large, invasive, pale-to-yellow neoplastic masses

• Distortion of normal renal architecture

What are common renal stromal tumors?

• Fibrosarcoma

• Leiomyosarcoma

• Hemangiosarcoma

What signalment is associated with renal tumors in dogs?

• Males 2× > females

• Opposite in cows (females > males)

Which renal tumor is extremely common in pigs?

Nephroblastoma

Embryonal tumor with:

• Primitive glomeruli

• Undifferentiated mesenchyme

• Tubular elements

What renal tumor is common in young dogs?

• Nephroblastoma (Wilms tumor)

• Often affects spinal region (“thoracolumbar spinal tumor of young dogs”)

Why can nephroblastomas cause neurologic signs in dogs?

Spinal form compresses spinal cord → hindlimb ataxia, paresis

What renal tumors are seen in cats?

• Carcinomas

• Lymphoma

• Nephroblastoma (less common)

Which renal tumor is most common in cattle?

Renal carcinoma

What common renal pathology is seen in goats?

Caprine kidneys often develop cystic changes and interstitial nephritis, especially with chronic infections