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Radiologists, Artists Solve Owl Neck Mystery

February 1, 2013
Written by: , Filed in: Cardiac Imaging, Musculoskeletal Radiology, Neuroradiology
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Neuroradiologists and medical illustrators at The Johns Hopkins University School of Medicine in Baltimore have teamed up to figure out how some owls can almost fully rotate their heads without damaging blood vessels or cutting off the blood supply to their brains.

Owls can rotate their heads as much as 270 degrees in either direction. Humans can’t spin their heads nearly as far. Even so, sudden head movements—such as those resulting from car accidents, roller coaster rides, even chiropractic manipulations—can stretch and tear human blood vessel linings. That can produce a clot, possibly leading to a pulmonary embolism or stroke.

Philippe Gailloud, MD, director of interventional neuroradiology at Johns Hopkins Medicine, explained his interest in owls:

Until now, brain-imaging specialists like me who deal with human injuries caused by trauma to arteries in the head and neck have always been puzzled as to why rapid twisting head movements did not leave thousands of owls lying dead on the forest floor from stroke.

Dr. Gailloud was quoted in a Johns Hopkins news release. “The carotid and vertebral arteries in the neck of most animals, including owls and humans, are very fragile and highly susceptible to even minor tears of the vessel lining,” he said.

He was part of a Johns Hopkins team, led by medical illustrator Fabian de Kok-Mercado, that used angiography and CT scans to solve the owl mystery. The researchers examined snowy, barred, and great horned owls that had died from natural causes.

It turns out that arteries at the base of an owl’s head are a lot bigger than human arteries, and there are a lot more connections between the carotid and vertebral arteries. Holes in neck vertebrae are much larger than the arteries that pass through them, so the artery isn’t constricted as the neck twists. The vertebral artery also enters the owl’s neck two vertebrae higher than in other birds, allowing for more slack in the artery.

The illustrated poster that presented the team’s findings won the Posters & Graphics category in the 2012 National Science Foundation’s International Science & Engineering Visualization Challenge. It’s featured, along with other winners and entries, in a February 1 special issue of Science.

In discussing the findings, Dr. Gailloud couldn’t resist sounding a warning: “Our new study results show precisely what morphological adaptations are needed to handle such head gyrations and why humans are so vulnerable to osteopathic injury from chiropractic therapy. Extreme manipulations of the human head are really dangerous because we lack so many of the vessel-protecting features seen in owls.”

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