What causes pedophilia (sexual attraction to children)?

Modern psychology still does not have a definitive cause (though this is true of many disorders), but I have been reading more about the neurological work done by Centre for Addiction & Mental Health in Canada. Dr. James Cantor did brain scans of pedophiles to try and fine common traits and also did outpatient therapy. One of the more interesting things is that a large proportion of them had blows to the head as children under 13, and this sometimes matches the age they are attracted to. The studies have also shown low white matter of the brain and decreased hypothalamic activity. They also tend to have low intelligence and other as-yet-unexplained differences in their brains. This research is still ongoing and it is hard to draw many conclusions from it, but it makes sense because I know in therapy settings pedophiles are extremely difficult to treat, often a combination of therapy not addressing the problem and pedophiles tendency to be delusional (i.e. thinking they are normal and that children are fine to have sex with). If their brains are "stuck" that way from an early age, it makes it hard for them to ever change.