Play was stopped for nearly 15 minutes on Saturday as Karunaratne was treated on the field before he was put on a stretcher and taken from the field to Canberra Hospital by ambulance.
Tim Paine's first declaration since taking over as Australian captain came midway through the middle session, ensuring Patterson had time to reach triple figures in just his second Test appearance. But the ball did not rise as high as he had expected, and struck him seemingly on the top of the shoulder, before hitting the area where his neck meets his skull.
Kusal Perera failed to return to the crease in the second test against Australia after he become the second Sri Lankan batsmen to retire hurt in their first innings.
Coach Chandika Hathurusingha said he was "in good spirits" and in "no danger".
The 30-year-old remained conscious but was set to receive further assessment after complaining of pain in his neck and tingling in his hands. He was talking to us before leaving (for hospital) as well. "But he was okay, was talking throughout to the umpires and the physio".
Embattled spearhead Mitchell Starc made a late breakthrough as Sri Lanka went to stumps at Manuka Oval at 3-123 in reply to Australia's 5 (dec)-534.
That ended Sri Lanka's solid opening stand, the best from a visiting team in Australia since England's Alastair Cook and Michael Carberry put on 85 in Perth in December 2013.
Coming into the match with a second-string bowling attack, Sri Lanka gave one boundary too many to the Aussies and paid the price for it.
The home side had struggled with the bat recently but have three centurions in Canberra already.
But he only lasted five overs after resuming on 172, adding eight runs before chopping a delivery from quick Kasun Rajitha onto his stumps.
At the other end Patterson, who earned a debut in Brisbane after hitting 157 and 102 for a Cricket Australia XI in a warm-up against Sri Lanka, reinforced his credentials as an exciting No.6.
The batsman initially had his helmet changed and continued batting, but after facing four balls to finish the over he sought medical attention.
Mewling leopard cub found in passenger's bag at Indian airport
A man smuggling a two-pound leopard cub was detained and arrested at the Chennai International Airport in India on Saturday. En route from Thailand to India, the man carried the month-old cub in a plastic grocery "basket" inside his checked luggage.
Will groundhog give good news for winter sufferers?
Since hedgehogs aren't native to the United States , another hibernating animal was chosen in their stead: the groundhog. Saturday, Punxsutawney Phil emerged from his burrow in Pennsylvania at sunrise and didn't see his shadow.
Osinbajo's Chopper Crash-lands In Kogi
Military officers can be seen in the clip trying to force open the helicopter and rescue the vice president and other occupants. The VP had gone to the college for the graduation ceremony of Senior Division Course 1/2018 participants.