[txrangerette]

An aneurysm?

[dawn53]

Here's the medline page on brain surgery:

http://www.nlm.nih.gov/medlineplus/ency/article/003018.htm

Here's the reasons for brain surgery from this site:

Brain surgery may be needed to treat:

brain tumors

bleeding (hemorrhage) or blood clots (hematomas) from injuries (subdural hematoma or epidural hematomas)

weaknesses in blood vessels (cerebral aneurysms)

arteriovenous malformations (AVM; abnormal blood vessels)
damage to tissues covering the brain (dura)

pockets of infection in the brain (brain abscesses)
severe nerve or facial pain (such as trigeminal neuralgia or tic douloureux)

trauma to the skull and repair of skull fractures

We know it's not a tumor, injury, trauma or tigeminal neuralgia...the rest would be anybody's guess.