Judy Woodruff:

U.S. tensions with Iran peaked earlier this month, when U.S. forces killed a powerful Iranian general, and Iran responded by firing missiles into bases in Iraq, with hundreds of U.S. troops on site.

No Americans were killed that night, but the Pentagon is now saying that 50 U.S. service members suffered traumatic brain injuries.

Why did it take so long to announce that number? And what makes brain injuries so difficult to diagnose and treat?

Here's Nick Schifrin.