What intrarenal (within the kidney) pathologies can cause anuria (lack of urine production), urinary tract obstruction, bladder obstruction, hydronephrosis (kidney swelling), and proteinuria (excess protein in urine)?

Intrarenal Pathology and Proteinuria

Among the options provided, proteinuria is the clinical manifestation most directly caused by intrarenal pathology. Intrarenal (intrinsic kidney) diseases primarily affect the glomeruli, tubules, interstitium, or renal vasculature, and proteinuria is a hallmark finding of glomerular and tubulointerstitial injury 1.

Understanding the Options

Proteinuria - The Intrarenal Manifestation

• Proteinuria is a direct consequence of intrarenal pathology, particularly glomerular diseases such as glomerulonephritis, which damage the glomerular filtration barrier 1
• The Mayo Clinic/Renal Pathology Society identifies proteinuria as a key indication for kidney biopsy to diagnose intrarenal diseases 1
• Intrarenal causes of proteinuria include:
  • Glomerulonephritis (immune-complex mediated, crescentic, proliferative forms) 1, 2
  • Acute interstitial nephritis (drug-induced in 80-90% of cases, or infection-related) 3, 2
  • Acute tubular necrosis (the most common intrarenal pathology) 3, 4
  • Vasculitis affecting renal vessels 3

Anuria - Not Typically Intrarenal

• Anuria (near-complete absence of urine) strongly suggests complete urinary tract obstruction or severe vascular catastrophe, not primary intrarenal disease 5
• While severe intrarenal disease can cause oliguria, true anuria is rare with intrinsic kidney pathology alone 5

Urinary Tract Obstruction - Post-Renal, Not Intrarenal

• Urinary tract obstruction is classified as post-renal kidney failure, occurring downstream from the kidney parenchyma 4
• Obstruction affects the collecting system, ureters, bladder, or urethra—not the kidney tissue itself 1
• However, chronic obstruction can eventually cause secondary intrarenal damage (chronic tubulointerstitial nephritis and fibrosis), but the primary pathology remains post-renal 6

Bladder Obstruction and Hydronephrosis - Post-Renal Findings

• Hydronephrosis is a radiographic finding of post-renal obstruction, detected by ultrasound with >90% sensitivity 1
• Bladder obstruction (from prostatic hypertrophy, tumors, or neurogenic bladder) causes bilateral hydronephrosis and is post-renal in origin 1, 6
• The ACR Appropriateness Criteria emphasize that hydronephrosis indicates obstruction at the level of the collecting system or below, not intrarenal pathology 1

Clinical Distinction Algorithm

When evaluating kidney failure, use this approach:

1. Check for obstruction first (post-renal):

   • Perform renal ultrasound to detect hydronephrosis 1, 5
   • Assess for bladder distension, palpable bladder, or suprapubic fullness 5
   • Anuria strongly suggests complete obstruction 5

2. If no obstruction, evaluate for intrarenal disease:

   • Urinalysis is critical 5, 4:
     • Muddy brown casts, tubular epithelial cells → acute tubular necrosis 5, 4
     • Red blood cell casts → glomerulonephritis 5, 4
     • White blood cell casts → acute interstitial nephritis or pyelonephritis 5, 4
     • Proteinuria → glomerular disease 1
   • Kidney biopsy is the gold standard for definitive diagnosis of intrarenal pathology 3, 4

3. Assess kidney size on ultrasound:

   • Normal-sized kidneys suggest acute kidney injury (including intrarenal causes) 1, 4
   • Small echogenic kidneys indicate chronic kidney disease 1
   • Increased echogenicity occurs in only 30-40% of acute intrarenal disease 1, 3

Critical Pitfalls to Avoid

• Don't assume hydronephrosis always means obstruction: Pregnancy, reflux, post-obstructive dilation, or diuresis can cause collecting system dilation without true obstruction 1
• Obstructive nephropathy can rarely occur without hydronephrosis: Retroperitoneal fibrosis or early obstruction may not show hydronephrosis on initial imaging 7
• Chronic obstruction causes secondary intrarenal damage: Long-standing post-renal obstruction leads to chronic tubulointerstitial nephritis, which may persist even after obstruction relief 6