Chronic urethral obstruction because of urinary calculi, prostatic hyperophy, tumors, normal pregnancy, tumors, uterine prolapse or functional disorders cause hydronephrosis which by definition is used to describe dilatation of renal pelvis and calculus associated with progressive atrophy of the kidney due to obstruction to the outflow of urine Refer Robbins 7yh/9,1012,9/e. P950