Why has my father suddenly become speechless?

Hello doctor,

My father aged 67 years old suddenly got speechless. When he woke up in the morning we went to throat specialist but there is no problem with the throat. We got computed tomography (CT) scan of the brain done. Then we had referred to the neurologist. He then immediately admitted to the hospital and the treatment started. Then we have done magnetic resonance imaging (MRI) of the brain, the neurologist said there is shrinkage in the veins of the brain. After the five days in the hospital, my father came home. But still he is speechless slightly a word he can say in a whole day. He can listen very well, understand everything, react to everything. blood pressure (BP), electrocardiogram (ECG), and two dimensional (2D) echo are normal. Complete blood count and blood sugar are also normal.