This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
The most common cause of renal scarring in a 3 year old child is: 
Select and explain. 
A. Trauma, B. Trauma, C. Vesicoureteral reflux induced pyelonephritis., D. Interstitial nephritis
C: Vesicoureteral reflux induced pyelonephritis.
Answer: C: Vesicoureteral reflux induced pyelonephritis. 
Explanation: Answer is C (Vesicouretrial reflux induced pyelonephritis): 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). - Mercks manual ( `In children < 10 yr, about 30 to 50% of UTIs are associated with vesicoureteral reflux (VUR) which can lead to renal scarring and renal insufficiency if not treated' - Merck's manual Remember :Renal tuberculosis is always secondary to some primary focus elsewhere in body and occurs later in life then other forms (commonly around 20-40 years age group.)