The vertebral artery is a pair of blood vessels in the neck that supply blood to the brain. These arteries work alongside the carotid arteries to ensure the brain receives a continuous supply of oxygenated blood. Understanding their anatomy and function is important for neurological health assessment.
The Vertebral Artery’s Path and Purpose
The vertebral arteries typically originate from the subclavian arteries, which are located beneath the collarbone. From their origin, each vertebral artery ascends through the neck, passing through specific openings in the cervical vertebrae, the neck vertebrae. They generally enter these openings, known as transverse foramina, at the level of the sixth cervical vertebra (C6), though occasionally this entry can occur at C7 or even higher, around C4.
As the arteries continue their upward path, they eventually enter the skull through a large opening at the base of the skull called the foramen magnum. Inside the skull, the two vertebral arteries merge to form a single, larger vessel known as the basilar artery, typically at the base of the pons, a part of the brainstem. This combined system, called the vertebrobasilar system, delivers blood to specific regions of the brain, including the brainstem, cerebellum, and the posterior part of the cerebrum.
Why Segmentation Matters in Radiology
The division of the vertebral artery into distinct segments is a standardized practice in radiology and clinical medicine. This segmentation provides a common language for healthcare professionals to precisely communicate about the artery’s anatomy and any abnormalities. This systematic approach allows for accurate localization of medical conditions affecting the artery, which can vary depending on the segment involved.
Segmenting the vertebral artery also guides diagnostic and treatment strategies. Different segments may be susceptible to particular types of issues, or require unique approaches for imaging, diagnosis, or surgical intervention. This detailed understanding of each segment’s characteristics supports more targeted and effective patient care.
Exploring the Vertebral Artery’s Four Segments
The vertebral artery is commonly divided into four segments: V1, V2, V3, and V4. Each segment has a specific anatomical course and can be associated with different radiological considerations. This classification aids in understanding potential pathologies along the artery.
The V1 segment, the pre-foraminal or pre-vertebral part, extends from the artery’s origin at the subclavian artery to its entry into the transverse foramen of the sixth cervical vertebra (C6). This initial portion runs upward and backward, positioned between the longus colli and scalenus anterior muscles. Radiologically, this segment is important as it is the most extracervical part and is sometimes affected by issues in the lower neck.
The V2 segment, or foraminal/cervical segment, travels upward through the transverse foramina of the cervical vertebrae, typically from C6 up to C2. Within these bony canals, the artery is surrounded by a network of veins that eventually form the vertebral vein. This segment’s encased course makes it susceptible to compression or injury from cervical spine conditions.
The V3 segment, also called the atlantic or suboccipital segment, emerges from the transverse foramen of the second cervical vertebra (C2). It then winds around the posterior arch of the first cervical vertebra (C1, also known as the atlas) and traverses the suboccipital triangle. This segment then enters the vertebral canal by passing under the posterior atlanto-occipital membrane. Its tortuous path in this region can make it vulnerable to mechanical stress.
The V4 segment, or intracranial/intradural segment, begins as the artery penetrates the dura mater, the tough outer membrane surrounding the brain and spinal cord, after passing through the foramen magnum. This final segment inclines medially, running along the front of the medulla oblongata, a part of the brainstem. This segment is located within the confines of the skull and is the portion that directly supplies the posterior brain structures.
How Doctors Visualize Vertebral Artery Segments
Doctors employ several imaging techniques to visualize the vertebral artery and its distinct segments, which helps in diagnosing various conditions.
- Magnetic Resonance Angiography (MRA) is a non-invasive method that uses a strong magnetic field and radio waves to create detailed images of blood vessels. It can provide clear representations of the artery’s lumen and surrounding tissues.
- Computed Tomography Angiography (CTA) is another non-invasive technique that uses X-rays and a contrast dye injected into the bloodstream. This method offers rapid, high-resolution images of the arteries, making it useful for detecting blockages or tears.
- Doppler Ultrasound is a non-invasive test that uses sound waves to assess blood flow within the arteries, helping to identify narrowing or blockages by measuring flow velocity.
- Digital Subtraction Angiography (DSA) is an invasive procedure considered the gold standard for detailed arterial imaging. It involves injecting contrast dye directly into the artery and taking X-ray images, with computer processing removing bone and soft tissue shadows to highlight the vessels.
Common Issues Affecting Vertebral Artery Segments
Various medical conditions can affect the vertebral artery segments, often identified through radiological imaging.
- Stenosis refers to the narrowing of an artery, which can restrict blood flow and lead to symptoms such as dizziness or stroke. The location of stenosis within a specific segment can influence treatment approaches.
- A dissection involves a tear in the inner lining of the artery wall, allowing blood to flow between the layers and potentially form a clot. This can lead to a sudden onset of neck pain, headache, or neurological deficits, and its presence in a particular segment guides intervention.
- Occlusion signifies a complete blockage of the artery, stopping blood flow to the brain regions supplied by that vessel.
- Aneurysms are abnormal bulges in the artery wall, which can weaken over time and potentially rupture, leading to bleeding.
- Atherosclerosis, characterized by the buildup of plaque within the artery walls, can lead to hardening and narrowing of the vertebral artery, increasing the risk of stroke.
- Vertebral artery hypoplasia describes an underdeveloped artery, meaning one vertebral artery is smaller than the other, which can sometimes affect blood flow distribution to the brain.