The vessels blocked by these clots are thinner than the width of a human hair, and they are critical for gas exchange in the lung. With clots choking off the lungs’ blood supply, these tiny vessels seem to make a desperate move, splitting down the middle in an attempt to get blood to these compromised areas -- a phenomenon called intussusceptive angiogenesis.

“What happens is that the blood vessel essentially drops sheet rock from ceiling to the floor. Now you’ve got a tunnel that actually splits into two,” says study author William Li, MD, president and medical director of the Angiogenesis Foundation.