It is dilatation of the renal pelvis and calyces associated with progressive atrophy of kidney due to obstruction to the outflow of urine. The signs and symptoms of hydronephrosis depend upon whether the obstruction is acute or chronic, partial or complete, unilateral or bilateral.
Specimen of markedly enlarged kidney
Cut surface shows marked dilatation of pelvi-calyceal system with thinned out cortex and medulla