Normally the oblique entrance of the ureter through the bladder wall causes ureteric occlusion during bladder contraction. In VUR there is a structural abnormality of the intra-mural ureter allowing reflux of urine from the bladder to the kidney. CIN becomes established leading to further renal deterioration. By an uncertain mechanism, interstitial nephritis may cause focal scars and initiate a slowly progressive renal deterioration.

Diagnosis is confirmed by demonstration of focal renal scars (IVU or isotope renogram; ultrasound less reliable for this); will also reveal other abnormalities, e.g. obstruction. Urine culture necessary to show infection. Assess renal function, proteinuria etc. in usual way.

http://www.edrep.org/pages/textbook/reflux.php

http://bjr.birjournals.org/cgi/content-nw/full/80/954/392/F5

Grade I - Reflux into the ureter only
Grade II - Reflux into the collecting system, without dilatation
Grade III - Reflux into the collecting system with mild dilatation, slight ureteral tortuosity, and no or slight blunting of the fornices
Grade IV - Moderate dilatation and/or tortuosity of the ureter and moderate dilatation of the renal pelvis and calyces, with complete obliteration of the sharp angle of the fornices but maintenance of the papillary impressions in the majority of calyces
Grade V - Gross dilatation and tortuosity of the ureter, with gross dilatation of the renal pelvis and calyces and nonmaintained papillary impressions



http://emedicine.medscape.com/article/414836-overview