Ohio State football coach Urban Meyer announced Tuesday he is leaving the program next month because of an arachnoid cyst that has gotten worse this year.

To learn more about the condition, The Enquirer spoke with local neurosurgeons Dr. Vincent DiNapoli of the Mayfield Brain & Spine practice, and Dr. Nicholas Marko of UC Health. The doctors emphasized they were speaking generally and were not involved in Meyer’s care.

What is an arachnoid cyst?

“Arachnoid cysts are interesting things,” Marko said. An arachnoid cyst is a pocket of spinal fluid in the brain's arachnoid layer, between the thick, leathery dura that lines the skull and the pia that hugs the brain itself like plastic wrap.

How did it get its name?

The arachnoid layer looks like a web of an arachnid, or a spider. When a cyst forms within that layer, it’s called an arachnoid cyst.

How do they develop?

Usually, you're born with one, the doctors said. For reasons that aren’t understood, DiNapoli said, the arachnoid layer separates from the other layers, and spinal fluid fills the gap. "Most of the time, these cysts are benign, they don’t progress, they don’t cause symptoms. Most of the time, we don’t even treat them, if they’re not changing over time.”

How common are arachnoid cysts?

No one knows, almost Marko estimated they might occur in about 1 percent of the population. It’s rare, but not freakishly so.

In October, Meyer announced he was undergoing treatment for an arachnoid cyst diagnosed in 1998. The coach said the cyst caused headaches that had worsened this year.

How do you know if you have this cyst?

"Most people don’t even know they have one,” Marko said, “unless you have to get an MRI for something else and the doctor says, you have an arachnoid cyst.”

Usually, spinal fluid keeps moving through the cyst, except more slowly than in other parts of the brain. But if fluid builds up, a patient can suffer headaches or speech problems or memory issues as the cyst presses on the parts of the brain that control those functions.

What happens once you're diagnosed?

Nothing, in about 99 percent of instances, Marko and DiNapoli said. The brain already adapted to the cyst. In the fraction of cases in which symptoms don’t improve, doctors tinker with the brain’s fluid dynamics. A medication called Diamox can inhibit production of spinal fluid, decreasing pressure in the brain.

In more serious cases, surgeons will drill into the skull and puncture the cyst, releasing trapped spinal fluid or improving flow. Two years ago, Meyer underwent that procedure. The brain, however, will heal over the surgical paths, and the surgeon will go back in and reopen the gaps to improve fluid flow. In the most severe cases, the surgeon can install a drain from the cyst into the abdomen.

Does a stressful job affect how a cyst grows?

The doctors said that by the time someone takes on a stressful job, the brain has already adapted to the presence of an arachnoid cyst. DiNapoli said stress by itself may not affect arachnoid cysts, but other issues around stress – poor sleep or diet, for example – can complicate life with an arachnoid cyst.

How big can an arachnoid cyst get?

Pretty small, maybe not more than a few millimeters in most cases, Marko said. In some instances, the cyst can get as big as a golf ball, but even then, doctors will leave the cyst alone. “People’s brains can develop perfectly normally even with a large cyst,” he said.