How a Moving Neck Bone Can Squeeze the Carotid Artery and Lead to Stroke

After breakfast, a 76-year-old man in Japan suddenly realized he had lost vision in his right eye. Doctors later found a blocked retinal artery and fresh, silent injury in his brain. Imaging showed that one of his carotid arteries was narrowed by about 50%, although ultrasound could not clearly visualize the affected section.

To get a better look, the medical team scanned him while he swallowed. Three-dimensional CT images revealed that his hyoid bone, the small U-shaped bone above the voice box, and a horn of the thyroid cartilage were pressing against the internal carotid artery each time he swallowed.

Researchers from Yamagata Prefectural Central Hospital described the case in a Radiology Case Reports paper. Similar reports published since then point to the same idea: when a bone is involved in artery injury, movement may reveal the cause.

A Bone That Moves With Every Swallow

The hyoid sits close to the point where the carotid artery divides in the neck. It supports the tongue and throat muscles and shifts every time a person swallows. Its relationship to the arteries can also change when the head turns.

In most people, that movement causes no problem. In some cases, however, the anatomy brings the structures into contact. The Yamagata authors noted that the man’s internal carotid artery had shifted inward to run behind the throat, a variation reported in about 2.6% of people, which may place the artery closer to the hyoid.

The doctors suggested that repeated compression could create shear stress, damage the artery’s inner lining, encourage plaque buildup, and lead to clot formation. Ultrasound could not show the narrowed section because the hyoid cast a shadow. After surgeons partially removed the hyoid horn and the thyroid cartilage horn, a repeat swallow scan showed no remaining compression. His recovery was uneventful, and he had no further events while taking aspirin.

A Swallow-Triggered Shift

Japanese neurologists have described one form of this movement as the flip-flop phenomenon, in which the carotid artery shifts from one side of the hyoid to the other during swallowing. In a 2018 study published in Cerebrovascular Diseases, ultrasound performed during swallowing with the neck turned found the phenomenon in 19.3% of 202 neurology patients.

People with the flip-flop motion were more than twice as likely to have significant narrowing of the internal carotid artery, at 30.8% compared with 12.9%. Among patients who did have narrowing, the motion was more common when the narrowing had caused symptoms. The study shows an association, not proof that the motion causes disease. Since then, researchers at CHU de Nîmes in France have completed a CT-based study examining how hyoid-carotid anatomy relates to narrowing and stroke.

Other reports show that the artery can be injured in different ways. Doctors in Chengdu, China, described an 80-year-old man with stroke and a dissecting aneurysm of the carotid artery in Experimental and Therapeutic Medicine. Ultrasound showed the hyoid compressing his artery repeatedly when he swallowed and spoke. He declined surgery and had no further strokes during follow-up while on antiplatelet medication.

Narrowing That Appears and Disappears

Because the problem may depend on position, a single scan taken while the head is still can look normal or uncertain. In a 2019 report in Annals of Vascular Surgery, a 32-year-old woman suffered repeated strokes from a clot in her right internal carotid artery. Ultrasound showed her hyoid lying between two branches of the carotid in a neutral neck position, then sliding across the internal carotid when she turned her head. After surgeons removed part of the bone, she regained full neurologic function and had no further events a year later.

Another report in Stroke described a woman whose carotid narrowing next to the hyoid disappeared on a scan four days later. She remained stable on aspirin, but four months later imaging showed the bone had shifted to the other side of the artery.

A 2025 case report described a 48-year-old woman in whom CT angiography showed hyoid compression of the right internal carotid artery, although the compression appeared only in certain head or arm positions, according to the PubMed abstract. She was also diagnosed with moyamoya syndrome, a separate disorder that narrows arteries inside the skull.

A German stroke center that reviewed 4,200 ischemic stroke patients treated over several years found six cases of these so-called bony strokes, or 0.14%. A commentary from the European Academy of Neurology warned that the retrospective design may underestimate the true frequency and urged dynamic exams of brain-supplying vessels in patients with repeated strokes in the same territory.

Rare, but Worth Considering

Most strokes are caused by familiar factors such as high blood pressure, abnormal heart rhythms, and plaque in the arteries. Bone-related compression is uncommon, and treatment decisions, including surgery to trim the bone, are made case by case without established guidelines.

The evidence remains limited. It is based mainly on case reports, small case series, and one observational ultrasound study, and dynamic scanning is not widely available everywhere.

Even so, the reports point to a useful possibility. When a stroke or eye artery blockage has no clear explanation, especially if events keep happening on the same side, patients and families can ask whether the neck vessels have been checked during swallowing or head turning.

No one should change eating habits or avoid turning the head because of these reports. Sudden facial drooping, arm weakness, speech trouble, or vision loss requires an immediate 911 call.

Key Questions Answered

What is the hyoid bone?

A small U-shaped bone above the voice box that anchors the tongue and throat muscles. It moves with every swallow.

How can it cause a stroke?

In people with certain anatomy, it can press on or rub the carotid artery, damaging the artery wall and allowing clots to form and travel to the brain or eye.

Why might standard scans miss it?

The contact may happen only during swallowing, speaking, or head turning, so a scan taken at rest can look normal or only mildly abnormal.

How common is it?

It is rare. One German stroke center found bone-related causes in 0.14% of ischemic strokes.

How is it treated?

With antiplatelet or anticoagulant medication, and in some cases surgery to trim the part of the bone touching the artery.

What should patients ask?

After an unexplained stroke, patients can ask whether imaging of the neck arteries during swallowing or head turning is appropriate.