The most common cause of renal scarring in a 3 year old child is –
The small scarred kidney in childhood:. Risdon RA] 'Reflux nephropathy is now a generally accepted term to describe small scarred kidneys discovered during childhood; it recognizes the close association between this renal lesion and vesicoureteric reflux (VUR)'.
Renal scarring is most commonly a result of chronic pyogenic infection of the kidney or chronic pyelonephritis. Chronic pyelonephritis occurs only in patients with major anatomic abnormalities, such as obstructive uropathy struvite calculi or, most commonly, VUR (in 30 to 45% of young children with symptomatic UTI).
Trauma
Tuberculosis
Vesicoureteral reflux induced pyelonephritis
Interstitial nephritis