One moment Mill Creek's 7-year-old Courtney McGrath was getting ready to go trick or treating -- the next, she was undergoing brain surgery.

The surgery is so risky that most doctors wouldn't even consider operating, but the right surgeon, the right treatment and the right time was everything.

Courtney McGrath doesn't like to talk about what happened to her, so she wrote about it to her second grade classmates:

"Dear Class, How are you doing? They needed to cut my skin so they could get to my brain..." she read. "I had big surgery at Harborview Hospital, the surgeons needed to get the AVM out of my brain."

What Courtney calls an 'AVM' is a tangled Web of abnormal blood vessels nesting on Courtney's brain. It had been since birth. Doctors don't know why.

"According to the doctors here, they had never seen a larger AVM in a child before," says Courtney.

Doctors told Courtney's mom it was a monster -- about the size of a pea.

For 7 years it went unnoticed, but on Halloween night, the 2nd grader turned cheerleader couldn't shake her pom-poms. Her left arm and leg went numb -- even her tongue and cheek started tingling.

The next day, an MRI revealed the Web of blood vessels.

"The brain, that's such a sensitive area," says Courtney's mom.

"I never had it before," says Courtney from her hospital.

It was in a dangerous spot -- the area that controls every motor skill in Courtney's body. Left untreated, it could paralyze her or cause bleeding on her brain.

"Blood loss can be phenomenal, a person can lose their blood and die," says Dr. Laligam Sekhar.

"I didn't know if she was going to be with me," says a teary Courtney.

"I likened it to dealing with an enemy army," says Courtney's doctor.

An army that Dr. Laligam Sekhar only recently could even try to defeat. Up until a year ago, Dr. Sekhar says it was too dangerous to operate on children to remove the large tangle of blood vessels.

Most surgeons wouldn't even try. Until now.

"Onyx helps us kill more enemy soldiers safely," says Dr. Sekhar.

Onyx is a new treatment. Injected into Courtney's blood vessels, this chemical acted like glue. The Onyx comes in contact with blood and hardens it. Once the blood hardened, Courtney's team of 5 doctors removed it safely.

Courtney called it "big surgery".

Try Mega-Big surgery -- 16 hours of patience and precision.

"Sometimes doing the surgery you feel like it's never gonna end," says Dr. Sekhar.

Two months after surgery, Courtney's brain is rewiring itself. She has to learn how to use her left arm and leg again. She's still your typical 2nd grader.

"Ha, ha. I won!" says Courtney.

Her brain just as sharp as always as she beats her twin brother at a board game. But, what happened to her, could still send Courtney back to Harborview.

It's not what you think.

"OK, let me listen to your heart," says "Dr." Courtney as she uses a real stethoscope to listen to her brother's heart. She's decided why be the patient when she can be the doctor? Paging Dr. McGrath?

OK, there's time for that later, but right now, she's got to finish second grade -- and that letter to her classmates...

"I miss you," says Courtney. "Signed, Courtney."

Right after Courtney's surgery, it appears there are no remnants of the abnormal blood vessels. But over the next 6 months, doctors say additional testing will have to be done to be sure.

And after another month of therapy, Courtney should be able to walk without her brace.