Is it important to rule out kidney anatomy issues in patients with abnormal post-void residual (PVR) ultrasound results?

Kidney Anatomy Assessment in Patients with Abnormal Post-Void Residual Ultrasound

Yes, it is important to rule out kidney anatomy issues in patients with abnormal post-void residual (PVR) ultrasound results to prevent potential morbidity and mortality related to upper urinary tract deterioration.

Rationale for Kidney Anatomy Assessment

Abnormal PVR measurements may indicate underlying urological conditions that can affect kidney function and structure. Here's why kidney anatomy assessment is crucial:

1. Upper Tract Protection: Incomplete bladder emptying can lead to vesicoureteral reflux and hydronephrosis, potentially causing kidney damage 1

2. Identification of Obstructive Causes: Kidney ultrasound can detect hydronephrosis, which may indicate urinary tract obstruction that could be causing the elevated PVR 2

3. Risk Stratification: The American Urological Association recommends kidney assessment as part of risk stratification in patients with lower urinary tract dysfunction 1

Clinical Significance of Abnormal PVR

• PVR >200-300 ml may indicate marked bladder dysfunction that could affect upper urinary tract 3
• Elevated PVR is associated with:
  • Increased risk of urinary tract infections
  • Potential for upper tract deterioration
  • Risk of renal insufficiency in men with poor flow 2

Kidney Assessment Protocol in Patients with Abnormal PVR

When to Assess Kidney Anatomy:

• Persistent Elevation: When PVR remains elevated on repeated measurements 1
• High-Risk Groups: Particularly important in:
  • Men over 60 years with feeling of incomplete emptying 4
  • Women of all ages with sensation of incomplete emptying 4
  • Patients with enlarged prostates (>30 ml) 1
  • Patients with renal insufficiency 2

Recommended Imaging Approach:

1. Ultrasound of Kidneys and Bladder:

   • Transabdominal ultrasound is the preferred non-invasive method 2, 1
   • Should evaluate both kidneys to identify unilateral or bilateral disease processes 2
   • Assess for hydronephrosis, which may be classified as:
     • Mild (Grade I)
     • Moderate (Grade II - "bear's paw" appearance)
     • Severe (Grade III - with parenchymal effacement) 2

2. Technical Considerations:

   • Right kidney: Use anterior subcostal approach with liver as window 2
   • Left kidney: Use intercostal approach due to lack of hepatic window 2
   • Patient positioning may need adjustment (decubitus position) to optimize views 2
   • Scan in both longitudinal and transverse planes 2

Clinical Interpretation and Management

• Normal vs. Abnormal: A PVR of <50 ml is considered normal in healthy young men 1
• Correlation with Symptoms: PVR-R (PVR ratio to bladder volume) >20% is associated with voiding disorders and >40% with severe dysfunction 5

Warning Signs Requiring Immediate Attention:

• Hydronephrosis with parenchymal thinning
• Bilateral kidney involvement
• Kidney stones or masses identified during ultrasound 2
• PVR >500 ml (associated with higher likelihood of requiring catheterization) 6

Common Pitfalls in Kidney Assessment

• Bladder Distension Artifact: A distended bladder can cause mild hydronephrosis in normal adults 2
• Dehydration Masking: Obstruction may be masked by dehydration 2
• Anatomical Variations: Reduplicated collecting systems, ectopic or horseshoe kidneys may be mistaken for pathology 2
• Medullary Pyramids: Can mimic hydronephrosis, especially in young patients 2

Documentation Requirements

Documentation should include:

• Indication for the procedure
• Description of organs studied
• Interpretation of findings 2

Imaging should be stored as part of the medical record when feasible 2.

By properly assessing kidney anatomy in patients with abnormal PVR, clinicians can identify potential upper urinary tract complications early and prevent significant morbidity and mortality related to renal dysfunction.