Todd Ewen spent 11 seasons fighting people in the NHL. From 1986 to 1997, the man known as “the Animal” in hockey circles wracked up 1,911 penalty minutes with the St. Louis Blues, Montreal Canadiens, Anaheim Mighty Ducks and San Jose Sharks. But parts of his post-hockey life were troubled. Despite a seemingly happy marriage and a successful real-estate business, Ewen suffered from bouts of depression and struggled with diabetes and lingering hockey injuries.

On the morning of Sept. 19, Ewen went to his basement and shot himself in the head. He was 49 and the seventh former NHL enforcer to suffer a seemingly early death in the past five years.

Given that and the growing body of research surrounding chronic traumatic encephalopathy — a degenerative brain disorder caused by repeated blows to the head — Ewen’s family suspected that he suffered from it, too.

“Every time it was announced that a fellow player had CTE, Todd would say, ‘If they had CTE, I know I have CTE,’ ” his widow, Kelli, said in a statement released by the Canadian Concussion Centre. “He was terrified by the thought of a future living with a degenerative disease that could rob him of his quality of life, and cause him to be a burden to his family.”

Ewen’s family donated his brain to the Canadian Concussion Centre for study, as CTE can only be diagnosed posthumously. But on Wednesday, the concussion researchers announced that Ewen did not have CTE, a sign that much more study is needed before we fully understand the consequences of repeated head injuries.

Said Lili-Naz Hazrati, a neuropathologist who conducted the autopsy on Ewen’s brain: “These results indicate that in some athletes, multiple concussions do not lead to the development of CTE. Our findings continue to show that concussions can affect the brain in different ways. This underlines the need to not only continue this research, but also be cautious about drawing any definitive conclusions about CTE until we have more data.”

In September, Boston University researchers announced they had studied the brains of 91 former NFL players and found 87 of them had CTE. But, as Branch notes, most of the brains were donated “by families searching to understand why their loved one’s behavior changed so radically in later years.” The fact that CTE can only be discovered posthumously makes tracking the actual rate of the disorder difficult, as the brains of deceased athletes who do not show the commonly accepted signs of CTE are not regularly studied.

In announcing its findings on Ewen’s brain, the Canadian Concussion Centre said it has now studied the brains of 20 former athletes. Only half showed signs of CTE. In May, for instance, it announced that former NHL player Steve Montador and an anonymous Canadian Football League player had CTE, while former CFL player John Forzani did not. All three had suffered multiple concussions over their careers.

“Although it is encouraging to see that not all athletes who sustain concussions will develop CTE, we still need to better understand this disease and the effects of concussions on the brain in order to figure out how to identify those who will develop CTE as well as help people like Todd Ewen who struggle with symptoms from head injuries,” said Carmela Tartaglia, a neurologist who was part of the Canadian Concussion Centre’s research team. “We are very grateful to the Ewen family for making this important contribution to research as it’s through these analyses that we hope to find answers.”