Letowski needed stitches to close a cut on his forehead and was diagnosed with a concussion at a nearby hospital. Coach Peter Laviolette said he would be released in time to fly with the team to Tampa for a game Monday night.
"He has a concussion, stitches - he got his bell rung," Laviolette said.
Letowski, a healthy scratch for Carolina's game Friday night against Atlanta, was skating up ice from the Hurricanes' end when he made a drop pass to teammate Eric Belanger between the circles. Moments after making the pass, and skating with his head turned in the opposite direction, Letowski was checked hard by Armstrong.
Armstrong's shoulder clipped Letowski in the head, causing Letowski to drop limply to the ice. The hit appeared to be clean and no penalty was called, but Laviolette complained his player was defenceless.
"It was a tough hit, it was unfortunate," Laviolette said. "You can make argument it was a little bit late. He had passed the puck, it was gone, one second, two seconds, and Trevor didn't see it coming."
Letowski landed face down on the ice at the top of the slot and lay motionless for several minutes. After he was lifted onto a backboard and then a stretcher, Letowski had his neck placed in a brace.
Armstrong defended his hit, but was visibly shaken by the injury.
"I don't think I'm a dirty player," Armstrong said. "I play hard. He moved it (the puck) and I hit him. I was finishing my hit on him. But you don't want that to happen to anybody. It's scary to me. . . . It did bother me."
In the second period, Penguins goalie Marc-Andre Fleury was lifted with Carolina up 3-0 after he was cut near an eyebrow during a scramble along the side of the net. After the Hurricanes finished up the 5-1 victory, he said his injury wasn't serious. Fleury was replaced by backup Jocelyn Thibault - the first time Thibault has played since having hip surgery following a Jan. 6 game against Atlanta.
Letowski's injury was the second by a Hurricanes forward in as many games in Pittsburgh in seven months. Forward Erik Cole broke his neck while being slammed into the boards by Pittsburgh defenceman Brooks Orpik in a March 4 game. Cole missed the rest of the season and did not return to the Stanley Cup champion Hurricanes until Games 6 and 7 of the finals against Edmonton.
Orpik drew a five-minute boarding penalty and was ejected for the hit on Cole. He was then suspended for three games.
Cole played Saturday night, going scoreless in 18 minutes, 37 seconds. Orpik has been out this season because of a broken hand.
The 29-year-old Letowski is playing in his eighth NHL season after signing with Carolina in July. He had 73 goals and 102 assists in 484 games, playing previously for Phoenix, Vancouver and Columbus. He had 10 goals and 18 assists last season with Columbus.