Amy C. Hughes was looking forward to a rare luxury: a leisurely weekday lunch with a friend at a restaurant near her suburban Philadelphia home.

Hughes, an engineer at Merck, had taken off the week after Christmas 2015 to spend time with her husband, Kevin, and their two children. The couple's son, Rion, then 13, had come down with a cold on Christmas Day and complained of a headache. A few days later, his pediatrician suspected a sinus infection and prescribed a three-day course of antibiotics.

But an hour after she headed off for lunch, she received an urgent call from her husband summoning her home. Three police cars and an ambulance were lined up in front of her house. A team of paramedics was attempting to resuscitate her son as they hurried out the front door to the closest hospital, 25 minutes away. His eyes were closed and his body was racked by a violent seizure.

At the hospital, the ER staff peppered them with questions about whether Rion used drugs. The seizures suggested a possible overdose, and a CT scan showed no signs of a head injury, another cause of seizures.

Rion, Hughes told the staff, has a mild form of autism and attention-deficit disorder; she wasn't sure he even knew what illegal drugs were.

In addition to the severity of the seizure they were struggling to control, doctors were worried about its extremely long duration. They believed Rion might have been having a seizure for more than an hour before his father discovered him and called 911.

For the next six days, doctors tried to determine why Rion, who had been healthy, suddenly developed a life-threatening seizure that seemed impervious to even high doses of anticonvulsants. The answer would turn out to be as disarmingly simple as it was uncommon.

Solution:

Because 13-year-old Rion Hughes was on a ventilator and needed specialized care, doctors at the community hospital decided to transport him to Children's Hospital of Philadelphia.

Heavily sedated, Rion was admitted to the pediatric intensive-care unit with a fever, and was given a spinal tap to look for an infection capable of triggering seizures, such as meningitis. He received three IV antibiotics and an antifungal drug, but no infection was identified in his spinal fluid.

After tests failed to find another cause, doctors told Rion's parents they suspected he had contracted a human metapneumovirus, a respiratory infection that typically affects the very young and the very old, and is most common in winter. The virus is typically mild and usually goes away without treatment in a few days; in some people, it can cause more serious illness.

Over the next few days, Rion began showing improvement and was taken off sedation and the ventilator and moved to a general pediatric unit.

Hughes was overjoyed that he showed no sign of brain damage. To ensure that he was never alone, Rion's parents and his grandmother, a nurse, took turns staying in the hospital with him.

At 6 a.m. on his sixth day in the hospital, his grandmother and mother awoke to find Rion in the midst of a seizure.

Surely, his mother thought, the virus had cleared his system. So why was he having a seizure?

A few hours later, when the medical team made rounds, Hughes questioned the doctors. They told her they thought some of the virus might still remain in his system, but they were upbeat about his progress. The plan was to send him home the following day, with instructions for an MRI scan of his brain in four to six weeks.

But Hughes asked whether the MRI could be performed while Rion was still in the hospital. The pediatrician on duty, Stacey R. Rose, ordered the scan.

That night, Rion was still in the MRI machine when a neurosurgeon approached Rion's father in the waiting room.

The scan showed that Rion had a massive infection in the subdural area of his brain that had breached the bony flap separating the brain from the sinuses. The infection had formed an abscess called an empyema, which triggered the seizures. Other symptoms of a subdural empyema include headaches and lethargy.

Before the advent of antibiotics, the condition, which is rare, was uniformly fatal. The problem disproportionately affects males between ages 10 and 40, and typically occurs during the winter.

Rion, his father was told, would need a procedure to relieve pressure that had built up inside his skull, and the area would need to be rinsed to rid it of infection. Surgery was scheduled for first thing the following morning. Rion made a full recovery, and was home nearly a week later.

Hughes said she asked doctors why they hadn't suspected an abscess, and was told the disorder is rare; she said she later learned that CHOP sees about one case a week in winter. Rose suspects the CT did not show the abscess because the test was not performed with contrast dye; an MRI scan is the definitive test used to diagnose it.

It's unclear why Rion developed an empyema. "I think it's just bad luck for some kids," Rose said.

The diagnosis, she said, surprised the medical team. "I think it's always important to be questioning the diagnosis," she said. "It's good to reevaluate."

Hughes, she added, was a "great advocate" for Rion.

Hughes said she will be forever grateful for the care her son received and especially to Rose "for listening to my concerns. I truly believe she saved his life."