The vertebral arteries (VA) are two major vessels that ascend through the neck to deliver oxygenated blood to the posterior portion of the brain. They supply the brainstem, cerebellum, and occipital lobes, which manage balance, coordination, and consciousness. Vertebral artery compression occurs when external pressure reduces the vessel’s internal diameter, restricting blood flow. This mechanical narrowing, or stenosis, is caused by various structures within the neck, leading to symptoms when the brain’s posterior circulation is compromised.
Compression Due to Chronic Skeletal Changes
Compression due to chronic skeletal changes involves fixed anatomical issues that exert continuous pressure on the vessel, regardless of head position. The most common cause is cervical spondylosis, a form of arthritis resulting from the wear and tear of spinal discs and joints. This degenerative process leads to the formation of bony growths called osteophytes (bone spurs) on the vertebrae. The vertebral arteries travel through bony tunnels called the transverse foramina. Osteophytes growing inward can narrow this canal, directly impinging on the artery.
Herniated discs in the cervical spine can also contribute to chronic compression. When the soft center of a disc pushes out, it can place pressure on the adjacent vertebral artery. Less frequently, compression is linked to congenital abnormalities, such as malformed vertebrae, which create an abnormally tight path for the artery.
Compression Triggered by Head Movement
Dynamic compression occurs only when the head or neck is moved into a specific position, such as rotation or extension. The most recognized form is Bow Hunter’s Syndrome (BHS), where the vertebral artery is temporarily occluded by head rotation. This syndrome primarily involves the upper cervical spine, typically at the C1 (atlas) and C2 (axis) levels.
When the head is turned, the C1 and C2 vertebrae rotate, causing the vertebral artery to be pinched or stretched against an adjacent bony prominence. Compression often occurs where the artery exits the transverse foramen of C2 and curves around the C1 vertebra. Soft tissues like fibrous bands, ligaments, or enlarged neck muscles can also become taut with rotation, squeezing the artery.
The obstruction is transient, lasting only as long as the head is held in the provocative position. Symptoms usually occur only if the contralateral vertebral artery is congenitally smaller (hypoplastic) or already compromised, preventing it from adequately compensating for the loss of flow.
Symptoms Resulting from Reduced Blood Flow
Restricted blood flow leads to Vertebrobasilar Insufficiency (VBI), affecting the brain areas responsible for coordination and consciousness. The sudden reduction in blood supply causes the brainstem and cerebellum to malfunction, resulting in neurological symptoms. These symptoms are paroxysmal, meaning they occur suddenly and briefly, usually resolving when the head returns to a neutral position.
The classic manifestations include:
- Vertigo, an intense sensation of spinning or dizziness, often accompanied by nausea and vomiting.
- Visual disturbances, such as double vision (diplopia) or transient loss of vision.
- Drop attacks, which are sudden, unexpected losses of muscle tone causing a fall without loss of consciousness.
- Difficulty with speech (dysarthria) and swallowing (dysphagia).
- Generalized gait instability or lack of coordination (ataxia).
These episodes signal temporary brain oxygen deprivation, similar to transient ischemic attacks (TIAs) in the posterior circulation. The positional nature of these symptoms helps distinguish VBI from other causes of dizziness.
Confirming the Diagnosis and Treatment Options
Diagnosing vertebral artery compression is challenging because its dynamic nature is often not visible on standard static imaging. Confirmation requires imaging the artery while the neck is in the position that provokes symptoms. Dynamic studies, such as Magnetic Resonance Angiography (MRA) or Computed Tomography Angiography (CTA), visualize blood flow and the point of compression during movement.
Digital Subtraction Angiography (DSA) is often considered the gold standard, providing a high-resolution, real-time view of the artery as the head moves, allowing precise pinpointing of the location and degree of occlusion. Doppler ultrasound is a non-invasive method used to screen for reduced blood velocity during neck movement.
Treatment begins with conservative strategies focused on managing symptoms and avoiding triggering positions. This includes physical therapy to improve neck posture, using a soft cervical collar to limit extreme movements, and anti-inflammatory medications. If compression is severe, recurrent, or leads to stroke, surgery may be necessary. The surgical approach is tailored to the cause, potentially involving removing a bone spur or fibrous band, or performing a cervical fusion to stabilize the vertebrae.