A sub arach hemorrhage is a leak in the blood vessels in brain.

It's a leak in the network of vessels that look like a spiderweb-hence the name-arachnoid.

Because the vessels are so small and wide spread, docs can get a general idea of where the hemorrhage is located, but they have to pinpoint the exact area of the rupture before they can open up the skull to repair it.

Not a good thing.