Two Marines spent years firing heavy weapons. Then came headaches and hemorrhage.

For Michael Lozano, it started with headaches that felt “like a needle” passing through his skull.

William Wilcox had headaches, too. Then, he says, “my head exploded.”

Both men had surgery to remove a brain arteriovenous malformation, a tangle of abnormal blood vessels prone to bleeding.

Both men suspect that their condition was linked to their years as Marine gunners exposed to repeated blast waves from the anti-tank weapons they fired.

That two Marines who did the same job in the same time period [the 1990s] would both be diagnosed with AVMs is “highly unlikely,” Wilcox says.

AVMs are estimated to be present in fewer than one in 1,000 people. There are about 200 gunners in the Marines at any given time.

Brain experts say the appearance of a rare brain condition in two gunners could still be a coincidence. But they also say there’s growing evidence that repeated exposure to blast waves can alter and damage blood vessels in the brain.

So is it reasonable for Lozano and Wilcox to wonder if their AVMs might be related to the time they spent firing heavy weapons?

“I think based on the research, that’s justified,” says Stephen Ahlers, a neuroscientist at the Naval Medical Research Command, which has been involved in much of the research on how blast waves affect the brain.

“It might happen,” says Dr. Ibolja Cernak, an expert on blast injury at Belmont University in Nashville. “We are gathering more and more information that primary blast does cause vascular changes in the brain.”

Similar paths

Lozano, 51, and Wilcox, 52, have a lot in common.

Both were Marine gunners in the 1990s trained to fire TOW (tube-launched, optically tracked, wire-guided) missiles. Both served at Camp Lejeune in North Carolina and took part in training exercises at Twentynine Palms, California.

Wilcox and Lozano trained extensively with rocket and missile launchers potent enough to disable a tank.

The most intimidating to operate was the Shoulder-launched Multipurpose Assault Weapon, or SMAW, which produces a backblast strong enough to kill a person nearly 100 feet behind the weapon.

“You could feel the concussion through your whole body,” Lozano says.

“Imagine a 300-pound linebacker hitting you in the chest at full speed,” Wilcox says. “Boom! It rattles your cage.”

Also, your brain.

Gunners place their heads just inches from the explosion that propels a missile or rocket from its launch tube.

The blast wave from these weapons is less powerful than the one produced by the sort of roadside bomb used to blow up Humvees in Iraq and Afghanistan. These bombs often caused a brain concussion, or knocked military personnel unconscious.

But gunners like Wilcox and Lozano are exposed to a blast every time they fire a heavy weapon.

One study done by the military found that SMAW operators were exposed to blast waves more than twice the level the military considers risky to a person’s brain at risk.

“Like the 4th of July on crack”

Wilcox lives in southern Virginia with his wife, Cynthia, and their dog, Leia. His mementos from the military include the launch tube from an AT4, a Swedish anti-tank weapon system.

Wilcox fired lots of weapons like the AT4 after joining the Marines in 1992.

He recalls one training exercise at Twentynine Palms where his platoon somehow got an extra allocation of missiles.”

“We go out on this mobile assault course and we’re firing them like crazy,” he says.

“As young men, it’s like Fourth of July on crack. We’re just loving every minute of this, never thinking in the future that some of these things could potentially impact us.”

The headaches began when Wilcox moved from Camp Lejeune to Quantico, in Virginia. They kept getting worse even after he left the firing ranges there to become a military computer systems specialist.

“I took Excedrin basically like candy,” he says.

In 2000, Wilcox left the military and took his computer skills to the private sector. Despite the headaches, he thrived.

Then in 2014, Wilcox and some friends go to Penn State for homecoming. They’re watching a band. Wilcox feels a headache coming on.

“I go out of the bar. I sit down on a bench. I put my elbows on my knees, and I notice that I’m losing control of my arms,” he says.

His arteriovenous malformation, that tangle of blood vessels in his brain, had begun to bleed. At the time, though, Wilcox was unaware of his condition.

A rare condition that can kill

An AVM is the result of abnormal growth or structural changes to blood vessels. Most are thought to be present at birth, though they can form in adults.

The condition is dangerous because it allows high pressure blood from the arteries to flow directly into relatively fragile veins. Normally, blood would go from arteries to capillaries, tiny vessels that reduce the pressure and turbulence, before reaching a vein.

An intact AVMs can cause headaches and seizures, but most go undetected unless they bleed.

Wilcox recalls an ambulance ride to a local hospital then a helicopter ride to the medical center in Hershey. Emergency surgery removed the AVM and probably saved his life.

“I spent about three weeks at Penn State Hershey relearning how to walk,” he says. Then he did three months of outpatient therapy.

Wilcox got better, but not enough to go back to his computer job. The bleed, and the surgery to fix it, left him with a big scar, several titanium screws in his skull and memory lapses.

“I do have brain damage,” he says when he thinks he’s repeating himself.

But the biggest challenge for Wilcox is epilepsy. Despite taking medication, he averages nearly one seizure a day.

“It’s brutal,” he says. “It wears me out physically, emotionally.”

For years, Wilcox did not connect his brain hemorrhage with his military service. Then a friend told him about Michael Lozano, another Marine gunner with an AVM.

PTSD and headaches

Lozano grew up in Ventura, California, skating and surfing. As soon as he turned 18, he joined the Marine Corps.

That was in 1991. Like Wilcox, he would spend years firing heavy weapons in training exercises.

In 2003, after 9/11, Lozano was sent to Iraq. There, he fired some of the same weapons in combat.

In the middle of one firefight, Lozano also got knocked senseless by the blast wave from a tank gun.

“I’m firing my M16, I look over to the side, and this tank just lights one right next to us,” he recalls. “You could feel the blast, the Humvee shook, I go sideways, and I’m kind of out of it.”

Lozano got a medal. He left the military in 2004. Then came the hard part.

“I wasn’t the same,” he says. “America was different.”

Lozano began having severe headaches, He also had PTSD, which led to lots of anger and alcohol. His first marriage ended.

Eventually, he found his way to a federal law enforcement training program in Georgia, where he met his second wife, Valery.

The headaches continued, though. And Valery Lozano, a forensic psychologist and clinical mental health counselor, noticed other signs.

“He wasn’t completing the files that we needed for work,” she says. “It just got to the point where, in my brain I was like, you know, something is not right.”

Eventually, she got her husband to a neurologist who found an AVM in Lozano’s right frontal lobe, the same place Wilcox had his.

Neurosurgeon Michael Lawton, president of the Barrow Neurological Institute in Phoenix, was able to remove the AVM before it bled. But Lozano’s memory problems and PTSD forced him to retire.

From war to Warhorse Ranch

Today, Michael and Valery Lozano run Warhorse Ranch near Steamboat Springs, Colorado. It’s a place they founded for veterans and others who’ve experienced trauma.

The ranch specializes in “equine assisted services,” which can mean simply talking about your problems in the company of one or more of the ranch’s 10 horses.

“When someone starts getting emotional, the horse will pick up on that and he’ll come over and stand right behind you or put his head on your shoulder,” says Adam Ramos, a Marine from Los Angeles who visits the ranch frequently. “It kind of helps you calm down.”

Michael Lozano says the horses (and one donkey) help him stay calm as well.

He often wonders, though, about whether his time firing heavy weapons led to his AVM.

His doctors told him, “You can either be born with it or you can experience some sort of trauma, which damages the vessels,” he says.

Lozano leans toward trauma. His surgeon, Dr. Lawton, has doubts.

“My initial answer is it’s probably not related, it’s probably coincidence,” Lawton says.

Most AVMs are caused by genetic abnormalities that affect the growth of blood vessels, he says. Still, he’s intrigued by recent studies that suggest blast waves can alter genes in the brain.

“It may be that the more we study this, we find that blast injury could be contributing to the same sort of genetic abnormalities,” he says.

At least one study in rats found that repeated blast exposure led to arteriovenous malformations in the brain. That study, like much blast research, was supported by the military and Veterans Affairs.

There is strong evidence, in both animals and people, that exposure to even a single blast can injure blood vessels in a way that initiates a cascade of repair mechanisms.

“After repeated blasts, these repair mechanisms could malfunction,” Cernak says, potentially leading to an AVM.

Facing uncertainty

Michael Lozano and William Wilcox are unlikely to get a definitive answer about what caused their malformed blood vessels, but they are encouraged that scientists are at least studying how blasts can alter veins and arteries.

They also support the military’s ongoing efforts to reduce exposure to heavy weapons blasts, especially in training.

In 2024, the Department of Defense issued a memorandum on “managing brain health risks from blast overpressure.”

It requires military leaders to identify, track and conduct cognitive assessments of “high risk” personnel, including those who operate anti-tank weapons. It also calls for more training using simulations instead of live ammunition.

In addition, the Marine Corps is shifting from heavy weapons like the SMAW to lighter weapons that expose operators to less blast force.

Wilcox says that’s a start.

“But also we need to help these guys when they get out if they do have an actual brain injury,” he says.