paediatric renal normal

background

  • 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

reference article

pediatric kidney size calculator

scan protocol

role of ultrasound

  • confirm normal anatomical position of kidneys
  • exclude structural anomalies.
  • assess size of the kidneys and collecting systems
  • exclude renal cortical scarring.
  • exclude renal or suprarenal masses (cystic or solid)
  • assess bladder filling and emptying
  • confirm bilateral symmetrical ureteric jets into the urinary bladder.

limitations

co-operation is the biggest challenge with any paediatric study.

if scanning a neonate, try to time the scan after a feed for best compliance.

patient preparation

this will vary.

supine is needed to assess the bladder.

often allowing the parent or care-giver to nurse the child provides better cooperation. scanning the kidneys from postero-laterally whilst a toddler cuddles the parent provides a good acoustic window.

equipment setup

5+mhz curvilinear probe

12mhz linear probe

warm gel

common pathology

neonatal and paediatric renal pathology can be broadly grouped into:

  • fusion anomalies. (horseshoe, ectopia, cross-fusion)
  • hypoplasia or agenesis.
  • duplication anomalies. (supernumerary or variants of the collecting system and uterers)
  • congenital structural disease (juveline pckd, mcdk, dysplasia)
  • solid tumour. (wilms,mesobalstic nephroma, nephrobasomatosis, rhabdoid)
*** ultrasound cannot exclude vesico-ureteric reflux ***

scanning technique

kidney

 using a curvil-inear probe:

  • 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

bladder

  • 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

kidneys:

  • longitudinal and transverse. with curved probe and linear array if possible
  • length measurement of the kidney
  • transverse measurement of the renal pelvis

urinary bladder:

  • longitudinal and transverse images
  • image showing the ureteric jets with colour doppler if possible (this requires patience)