Doctors treating a teenager following a head knock at school have made a potentially life-saving discovery.

A routine CT scan to check for injury revealed a cyst and mass and within hours Rudolf Oosthuizen, 14, was in emergency brain surgery.

WATCH THE VIDEO ABOVE: Ticking time bomb found on boy’s brain after head knock.

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The Perth teen had bumped heads with a friend during a sports class two weeks ago.

The only sign something was wrong afterwards was a bruised eye, a headache and a feeling of tiredness.

His father knew something was not right and took him to Joondalup Hospital’s emergency department a few days later.

That is when the ticking time bomb was discovered on Rudolf’s brain.

He was rushed to Perth Children’s Hospital for a six-hour surgery to remove the growth.

“We are calling it the luckiest bump ever because without this bump to the head we would not have known there was something in there or something was happening” his father Rudolf Snr Oosthuizen told 7NEWS.

“We don’t know would have happened if we didn’t know.”

Rudolf and his family face a nervous road ahead.

It will take a week for test results to come back telling them exactly what the mass on his brain was — and what their future holds.

The community has rallied behind him, with a GoFundMe set up to help with ongoing medical costs and household bills.

“I miss my friends but schoolwork can wait,” Rudolph said.