Urinary bladder cyst
is mostly congenital, this is common with other congenital abnormalities like polycystic kidney
There are also other causes for bladder cyst but they are uncommon in a child.
The symptoms of urinary bladder cyst are usually pain during urination, difficulty in urinating, fever
These symptoms ressembles UTI. and UTI is also common in bladder cyst.
Urine culture may not be positive for growth. and even if it is UTI there must be a minimum number of organism present for growth.
Get your child with USG report to a paediatric surgeon. He may suggest you better.