The South Australia batsman, who would have turned 26 on Sunday, was fatally injured when hit by a "bouncer," a short ball that bounces up towards the batsman's torso, near his left ear -- the ball somehow evading the cricketer's helmet as he swiveled to play a shot.
Australian team doctor Peter Brukner told a press conference Thursday that Hughes suffered a "massive bleed into his brain" during the game on Tuesday afternoon.
He said the ball hit the side of his neck and, "as a result of that blow, his vertebral artery was compressed by the ball. That caused the artery to split and for bleeding to go up into the brain. And he had a massive bleed into his brain. This is frequently fatal at the time."
But he said doctors on the scene, including a specialist who had been in the crowd, managed to resuscitate him. He was later taken to hospital where they made "an intervention" to release pressure on his brain. He was then put in an induced coma but failed to recover.
Speaking at the news conference, Brukner explained that Hughes had died as a result of "vertebral artery dissection".
He said the artery had been compressed, causing it to split and leading to a "massive bleed" into the brain.
Brukner said the injury was "freakish", adding: "Vertebral artery dissection is incredibly rare. If you look in the literature, there is only 100 cases reported. There is only one previous example caused by a cricket ball."
Dr Tony Grabs, who treated Hughes at St Vincent's, said scans had shown that the stricken cricketer needed surgery quickly to help get the pressure down in the brain.
"He had extensive surgery to remove some of the skull from around his brain to help allow the brain to expand," added Grabs.
However, his recovery did not go as hoped.
"Over a period of the first 24 to 48 hours, he did not make very much improvement and unfortunately, as a consequence of the injury, he died,'' said Brukner.
The Australian flag was lowered to half-mast over the Sydney Cricket Ground where Hughes suffered the horrific injury. Flags were also lowered at the iconic Melbourne Cricket Ground.
Australian Prime Minister Tony Abbott paid tribute to Hughes, describing him as "a young man living out his dreams".
"His death is a very sad day for cricket and a heartbreaking day for his family. What happened has touched millions of Australians," he said.
"For a young life to be cut short playing our national game seems a shocking aberration. He was loved, admired and respected by his team-mates and by legions of cricket fans."
Australia coach Darren Lehmann tweeted: "RIP you little champ, we are all going to miss you! Love, prayers to all the Hughes family."