Luke Galloway died at age 22 by suicide, 19 years after being struck on the head by a playground swing. The two events were connected.

His mother, Claire, tells his story in a heart-wrenching new book, “A Call to Mind: A Story of Undiagnosed Childhood Traumatic Brain Injury.” Here, she reveals several truths about traumatic brain injury and how it’s too often overlooked by those who are supposed to diagnose and treat it.

Traumatic brain injuries (TBIs) can be devastating. When a person suffers a blow to the head — due to sports injury, military combat, a car crash, a fall, a violent attack, or some other accident or event — it can alter his or her brain function and behavior.

For some, the change is temporary. For others, it never goes away. And for some, whose injuries remain unidentified and untreated, it can set off a spiral into depression, substance abuse, criminality, homelessness, or suicide.

Yet, as dire as TBIs can be — and as common as they are (1.7 million per year, estimates the CDC) — there’s a shocking lack of knowledge and resources around them.

Galloway’s son, Luke, suffered a closed-head TBI at a park playground at almost 3 years old. As she and her husband were spreading out blankets by the pool, they took their eyes off Luke for a few seconds. He darted away and into the descending arc of a child on a hard plastic swing. It struck him on the head and sent him flying. As Galloway rushed to him, she feared he might be dead. He wasn’t. But he was forever changed.

Luke was visibly dazed from the blow. But because there were no other obvious signs of concussion or external injury, the pediatrician advised against an emergency room visit. But even as the family waited out the recommended 24-hour observation at home, it was clear to Galloway that something was seriously wrong. Her happy-go-lucky little boy had transformed into an anxious and easily agitated child.

Suddenly, Luke was fearful of going to bed. He clenched his fists and shook his arms in what were later (much later) diagnosed as mini-seizures. As he grew up, other symptoms appeared.

He complained of noises in his head. He experienced synesthesia. He got “stuck” in thoughts he couldn’t move through. He struggled in school (despite his high IQ). He became socially isolated. He began to act out impulsively, and, eventually, depression set in.

Luke wasn’t diagnosed with a brain injury until he was 18 years old. By then, years of psychological overlay, frustration, and shame had taken their toll. When he finally lost all hope, he bought a gun, put it to the exact area of his head that had suffered the injury, and pulled the trigger.

In the wake of this terrible loss, Galloway has been determined to raise awareness for others about the scope and impact of unidentified TBI, especially closed-head injury. She wants physicians, educators, psychologists, family, friends, and parents to better recognize how a TBI can manifest so it can be identified and treated as soon as possible.

She offers the following insights and advice for parents:

• Take every bump on the head seriously.

If your child loses consciousness, even briefly, or seems dazed and confused, vomits, or shows unequal dilation of the eyes, seek medical help right away. Also, be aware of any other unusual behavior — for instance, Luke didn’t cry, which is not normal for a toddler.

• Make sure your child’s doctor takes them seriously as well.

Many physicians lack a precise protocol for diagnosing head injuries, so parents need to understand what the issues are, says Galloway. If you’re seeing worrisome symptoms in your child and your pediatrician doesn’t order appropriate testing and follow-up, you may need to seek emergency or urgent care to have your child assessed.

• Be aware that many TBIs go undiagnosed.

Many TBIs remain undiagnosed because physicians don’t believe the parent’s report of behavioral, emotional, or physical changes in their child. Or they might initially diagnose a concussion, but then dismiss a parent’s observations of lasting changes, assuming the injury has healed.

Also, parents may notice changes in their child but don’t realize that he fell off the monkey bars at school (or, they realize it but don’t connect the strike to the head with the subsequent symptoms).

• Know that brain scans don’t always show a TBI.

Sometimes, evidence never shows up on a scan. If your child does have a scan after a strike to the head and it appears to be clear, don’t take this as proof that nothing is wrong. There are neuropsychological tests that can be administered that provide as much or more information than a scan.

• For treatment, time is of the essence.

The earlier your child’s TBI is identified, the better. He will then have the help he needs in school, and his peers and family will be taught to understand and to be his support system.

• TBI may masquerade as a behavior issue.

Luke exhibited unexplained delays in emotional maturation, behavioral outbursts, and social difficulties. All of these were clues that, had they been connected to his history of having had a blow to the head, could have led to an earlier diagnosis.

• The effect of TBI might not be immediate.

Children often “grow into” their injury as they access different parts of the brain at different ages. For example, when Luke grew into the need for executive brain functioning — such as planning, flexibility of thought, self-awareness, impulse control, organization, time management, working memory, and self-control — he suddenly couldn’t complete higher-level assignments or read higher-level books.