Which imaging finding most strongly suggests post-renal obstruction as the AKI cause?

• A. Hydronephrosis on renal ultrasound or CT.
• B. Diffuse renal cortical thinning without dilation.
• C. Normal kidneys on imaging.
• D. Small, contracted kidneys with increased echogenicity.

Answer: (A)

In obstructive kidney injury, urine cannot exit the renal system, so pressure builds up behind the blockage and the collecting system dilates. Hydronephrosis seen on renal ultrasound or CT directly reflects this upstream dilation from a post-renal obstruction, making it the strongest imaging clue that AKI is due to an obstructive cause.

Other imaging patterns point to different problems: diffuse cortical thinning without dilation suggests chronic parenchymal damage rather than an acute obstruction; normal kidneys on imaging offer no evidence of obstruction; small, contracted kidneys with increased echogenicity imply chronic kidney disease or scarring rather than an acute blocked flow.