Hit my head, MRI indicates white matter hyperintensities?

I had severe headache stay for two weeks which started after when my forehead hit with piece of wood. Then i have done MRI in which report says white matter hyperintensities found. some time i feel hard to remember new task and feel sleepy even after 8 hour sleep.
please tell me what are these white matter hyperintensities and how can we cure it. what is the side effects of i.