My Son Is 5 Months Old. He Has Prominent Left

my son is 5 months old. he has prominent left pelvicalyceal system. left ap diametre of pelvis measures 5.0 mm. no evidence of any calculus / mass is seen.left kidney size is 6.2 cm and right kidney is 5.5 cm. other things are normal and within range. in 1 months of his age left ap diametre was 3.0 mm. and when he was born it was 4.7 mm. please suggest the treatment