What is the recommended workup for a patient with mild hydronephrosis (swelling of the kidney due to urine flow obstruction)?

Workup for Mild Hydronephrosis

The recommended initial workup for a patient with mild hydronephrosis should include renal ultrasound with Doppler imaging, followed by CT urography or MR urography based on clinical context and patient characteristics. 1, 2

Initial Evaluation

Imaging Studies

1. Renal Ultrasound with Doppler

   • First-line imaging modality for all patients with suspected hydronephrosis
   • Evaluates:
     • Degree of collecting system dilation
     • Renal parenchymal thickness
     • Presence of hydroureter
     • Bladder abnormalities
   • Grading of hydronephrosis:
     • Mild (Grade 1-2): Renal pelvis dilation <15mm without significant calyceal dilation
     • Moderate to Severe (Grade 3-4): Renal pelvis dilation >15mm with calyceal dilation 2

2. Follow-up imaging based on clinical context:

   • For non-pregnant adults:

     • CT Urography (CTU) without and with contrast
     • MR Urography (MRU) without and with contrast 1

   • For pregnant patients:

     • Ultrasound or MRU without contrast (to avoid radiation and gadolinium) 2

Functional Assessment

• Diuretic Renal Scan (Tc-99m MAG3)
  • Indicated for moderate to severe hydronephrosis
  • Evaluates renal function and urinary drainage
  • Preferred over DTPA for suspected obstruction or impaired renal function 1
  • Criteria suggesting significant obstruction:
    • T1/2 >20 minutes on diuretic renal scan
    • Decreased renal function (<40% differential function)
    • Deteriorating function (>5% change on consecutive scans) 2

Special Considerations

Bladder Assessment

• Voiding Cystourethrography (VCUG)
  • Indicated when vesicoureteral reflux (VUR) is suspected:
    • Bilateral hydronephrosis
    • Hydroureter
    • Abnormal bladder findings
    • History of UTIs 2

Technical Considerations for Ultrasound

• Patient Preparation:

  • Ideally scan bladder before voiding and kidneys after voiding
  • Note that a distended bladder can cause artifactual mild hydronephrosis 1

• Scanning Technique:

  • Right kidney: Anterior subcostal approach using liver as window
  • Left kidney: Intercostal approach (lacks hepatic window)
  • Use of curved array transducer (2-5 MHz) for adults
  • Higher frequency transducer (5.0-7.0 MHz) for children and smaller adults 1

Follow-up Recommendations

• Mild Hydronephrosis:

  • Follow-up ultrasound in 1-6 months
  • Resolution rate of 64-73% can be expected 2

• Moderate to Severe Hydronephrosis:

  • More frequent follow-up (every 1-3 months initially)
  • Consider antibiotic prophylaxis
  • Consider functional studies (MAG3 scan) 2

Common Pitfalls and Caveats

1. Artifactual Hydronephrosis:

   • Full bladder can cause temporary mild hydronephrosis; scan kidneys after voiding 1

2. Pregnancy-Related Hydronephrosis:

   • Occurs in 70-90% of pregnant patients
   • Typically asymmetrically prominent on the right side
   • Often physiologic and resolves after delivery 2

3. Mild Hydronephrosis and VUR:

   • Poor correlation between mild hydronephrosis and vesicoureteral reflux
   • VCUG may not be necessary in asymptomatic patients with isolated mild hydronephrosis 3

4. Prognostic Value:

   • In ureteral colic, absent or mild hydronephrosis identifies patients with lower risk of passage failure (15-20%)
   • Severe hydronephrosis is associated with higher passage failure rates (43%) and warrants definitive imaging and referral 4