When Cristy Hardy started dating her now-husband, Kyle, he had a “crazy scar” from brain tumor surgery a year earlier. The benign tumor had been removed and he didn’t think much of it, so she didn’t either. As time when on, his follow-up appointments were few and far between. He continued working as an electrician, and they got married and had two kids – a perfectly ordinary life.

Then, in 2011, seven years after his initial surgery...