The normal ultrasound appearances of the kidney vary with age.
Initially, in the neonatal period, there is almost no medullary fat.
The pyramids are visibly prominent and hypoechoic. They span almost the entire cortex.Be cautious not to mistake them in the neonate as prominence of the collecting system.
Beyond 1 year old the kidneys take on a more typical appearance with better differentiation between medulla and cortex and less prominent pyramids. Depending on the habitus of the child, there will still be minimal echogenic medullary fat.
In both the neonatal and paediatric kidney, the foetal cortical lobulations are pronounced and should span the pyramids (as seen in the images below). If a lobulation dips into a pyramid, it is likely to be a cortical scar.
A neonatal kidney ultrasound.
This kidney has a distended collecting system secondary to a PUJ
Performed with a 12MHz linear array probe.
Note the abscence of medullary fat.
A normal neonatal kidney ultrasound.
Note the prominant pyramids and cortical lobulations spanning them
Assess the kidneys in both longitudinal and transverse sections from the flank. Because the lower ribs are not densely ossified, you can use an ‘intercostal approach.
Ensure you sweep entirely through the kidneys in both planes, particularly beyond the upper pole to exclude adrenal pathology. This may be best achieved more cranially, using the liver as an acoustic window.
Be cautious of over-calling hydronephrosis if in a coronal plane. The calyces may be very obvious but still normal if approached from the coronally. Confirm calycael dilatation also in the transverse/axial plane.
Obtain an accurate length measurement of each kidney, reproduced at least twice.
Using a higher frequency(10-12MHz) Linear probe:
Reassess the kidneys with a focus on the cortex and medullary pyramids.
Look for cortical scarring. This will be evident as linear echogenic line from the cortical edge in towards a pyramid. Do not confuse normal lobulations which will span the pyramids.
Look at the echogenicity of the pyramids. They should be hypoechoic. Any increased echogenicity is suggestive of a nephritis. If the pyramids have echogenic lines throughout, this is likely severe pyelonephritis
Begin in transverse with a slight caudal angle. Sweep trough the bladder for any structural defects or focal wall thickening.
Apply colour/power doppler to look for ureteric jets. This may require patience. Confirm there are 2 and they are reasonably symmetrical with no residual distal ureteric dilatation or ureteroceles.
Basic Hardcopy Imaging
Longitudinal and Transverse. with curved probe and linear array if possible
Length measurement of the kidney
Transverse measurement of the renal pelvis
Longitudinal and transverse images
Image showing the ureteric jets with colour doppler if possible (this requires patience)