Hi, I'm Loch MacDonald.
I'm a professor of Neurosurgery at
the University of Toronto and I'm going to talk to you about Subarachnoid Hemorrhage.
Subarachnoid hemorrhage is characterized by
a very consistent clinical scenario of
sudden onset of the most severe headache of a person's life.
It's a pathological condition,
which you can see here on this CT scan on the left side,
which shows subarachnoid blood,
and in the picture of the base of the brain on the right from
a person who has subarachnoid hemorrhage and unfortunately hasn't survived.
So today we're talking about spontaneous subarachnoid hemorrhage.
Trauma, or anytime somebody is hit on the head can cause
subarachnoid bleeding just from the trauma and shaking of the brain,
and that's actually a common cause of subarachnoid hemorrhage,
but we're talking about the spontaneous cases where there's no trauma.
Causes of spontaneous subarachnoid hemorrhage,
if we take a circle and divide it into thirds,
you can see that two-thirds plus a half of the other third,
so about 85 percent of cases, are due to ruptured aneurysms,
which you can see on this CT angiogram,
the remaining 15 percent or so,
or half of a third are nonaneurysmal spontaneous subarachnoid hemorrhages.
Subarachnoid hemorrhage is a pathological condition,
it's bleeding in the subarachnoid space,
it's not a disease entity,
but a pathological condition due to multiple different causes.
As I said, for the spontaneous cases,
about 85 percent are aneurysmal,
of the remaining 15 percent,
about two-thirds of those are a specific condition called
nonaneurysmal perimesencephalic subarachnoid hemorrhage,
which used to be called benign perimesencephalic hemorrhage,
but the former term is preferable now.
The remaining five percent or so are due
to other causes like brain vascular malformations,
venous thrombosis, pituitary apoplexy, and coagulation disorders.