Brief Answer:
Collection of blood on brain surface.

Detailed Answer:
I read your question and I understand your concern.

The brain has 3 membranes covering its surface called the meninges. The names of each layer starting from the outer one are dura matter, arachnoid matter and pia matter.

A subdural hemorrhage is a collection of blood under the dura, between dura matter and arachnoid matter, usually due to a torn vein on the surface of the brain. The fall and the hit he has taken are the cause of the torn vein, but the blood thinner he was taking facilitated it by preventing blood clotting.

The symptoms depend on the quantity of blood accumulated, if only a thin layer of blood may even be asymptomatic, the more blood there is, the bigger the chances of increased pressure on the brain causing symptoms like confusion, headache, drowsiness, seizures. If pressure is very high it could lead to coma and death.
So depending on the blood quantity often surgery is needed to evacuate the blood.

Technically it's a fairly easy routine procedure for the neurosurgeon and some improvement is expected. How well he will recover depends on the amount of blood on his CT and how much damage the raised pressure has already done. Of course his current condition is an indicator of the damage, the fewer symptoms he has the better the outcome.

Also in his prognosis it is also to be considered that there will be some added risk for stroke due to blood thinners interruption for some time.

I remain at your disposal for further questions.

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Brief Answer:
Yes the earlier the better

Detailed Answer:
Naturally it would have been better if it was discovered earlier. Since 6 weeks passed means it is a chronic hemorrhage. If he went on taking Warfarin it has prevented bleeding from stopping and what was possibly a small tear and bleed initially, went on making for more and more blood accumulating. If discovered earlier and warfarin was interrupted the size might have been smaller. That is often the case with chronic hemorrhages though, they are pretty insidious in their course
Surgery itself as I said is routine procedure, but of course his general condition and other medical issues play a role in the prognosis. If he has suffered neurological deficits full improvement might need some weeks, but most patients return to their previous level of functioning. On the other hand if his actual pre-op condition is good, alert and oriented, with no major deficits then should be out of hospital very soon. A follow-up CT will be needed as there is a 10-15% chance of rebleed.

I hope to have been of help.

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