ULTRASOUND - KIDNEYS

 Alternative Names:  renal ultrasound, renal sonography, ultrasound of the kidneys, renovascular ultrasound

INDICATIONS FOR RENAL ULTRASOUND

• Flank pain

• Haematuria (frank or microscopic)

• Follow-up of previously identified pathology

• Classification of a mass (Solid V's cystic)

• Post surgical complications

• Guidance of aspiration, biopsy or intervention

• Post injury

LIMITATIONS OF RENAL SONOGRAPHY

• The mid to distal ureter is generally obscured by bowel gas.

• Small lesions at the upper pole of the kidney may be difficult to see due to refractive edge shadowing.

• This can be overcome with thorough scanning technique.

EQUIPMENT SELECTION FOR RENAL ULTRASOUND

• Highest frequency curved linear array probe possible.

• Start with 7MHz and work down to 2 or 3 for larger patients. Assess the depth of penetration required and adapt.

• Paediatric and thin patients should be scanned with a 7MHz.

• Good colour / power / Doppler capabilities when assessing vessels or vascularity of a structure.

PATIENT POSITION FOR RENAL ULTRASOUND

• Begin with the patient supine.

• Each kidney may also need to be examined in the decubitus position.

• Raise the ipsilateral arm above the patient's head.

TECHNIQUE

• A comprehensive examination of the renal tracts should always include assessment of the urinary bladder and, in males,the prostate.

• Scan longitudinally right subcostally.

• Visualise the kidney inferior to the right lobe of the liver (RT), or spleen (LT).

• Place the probe between iliac crest and the lower costal margin to examine in the coronal plane.

• Ensure the kidney is thoroughly examined from edge to edge. Rotate into transverse. Scan from beyond the superior margin to inferior.

• Document the normal anatomy and any pathology found, including measurements and vascularity if indicated.

WHAT TO ANALYZE DURING THE RENAL ULTRASOUND

• Kidney size (should not be >1cm difference between sides)

• Cortical thickness(not <10mm)

• Cortico-medullary differentiation

• Cortex at least as hypoechoic as the liver

• Pyramids slightly hypoechoic relative to the cortex

• No hydronephrosis

• Renal scarring(beware mistaking prominant lobulations as scars)

COMMON NORMAL VARIANTS

• Unilateral renal agenesis

• Atophic small kidney

• Horseshoe kidney

• Ectopic kidney

• Duplex kidney

• Cross fused ectopia

COMMON PATHOLOGY

• Calculus

• Renal cyst

• Cortical

• Parapelvic

• Angiomyolipma

• Renal cell carcinoma

• Transitional cell carcinoma

RENAL ULTRASOUND SAMPLE PROTOCOL (TYPICALLY)

This sample protocol is meant for educational purposes and the exact technique will depend on the patient's clinical indication for the examination and the radiologist's guidance.

1. Right kidney long (measure distance)

2. Right kidney short axis (measure transverse and mediolateral)

3. Right kidney lesions should have 3 measurement and doppler flow characterization

4. Right kidney long including the liver for comparison of echogenicity

5. Left kidney long (measure distance)

6. Left kidney short axis (measure transverse and mediolateral)

7. Left kidney lesions should have 3 measurement and doppler flow characterization

8. Left kidney including the spleen for comparison of echogenicity

9. Left kidney long with liver for comparison

10. If there is hydronephrosis, take images of the distal ureters and urinary bladder looking for a point of obstruction.

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