Hydronephrosis is a distention of the renal calyces and pelvis with urine as a result of a urinary outflow obstruction.
Use this mnemonic 'PACT SUPER' to memorize the differential diagnoses of hydronephrosis.
Unilateral is PACT:
Pelvic-uteric obstruction (congenital or acquired)
Aberrant renal vessels
Tumours of renal pelvis
Bilateral is SUPER:
Stenosis of the urethra
Extensive bladder tumour