What can damage the the upper brain stem?

Multiple problems. in older folks, local strokes, either from end arteries within stem, or without in vertebrobasilar circulation. Might have significant trauma causing vertebral artery dissection. Can see midline posterior tumors, mainly in children. Can be an area of involvement in multiple sclerosis, vasculitis, sarcoidosis, Lyme disease, etc. If there seems localized damage, an answer is needed.