A Magnetic Resonance Imaging (MRI) scan of the cervical spine uses strong magnetic fields and radio waves to create detailed pictures of the neck region. This non-invasive imaging technique is highly effective for visualizing soft tissues like the spinal cord, nerves, and intervertebral discs, which are often the source of neck pain and neurological symptoms. Understanding how to interpret these images and their accompanying reports can help a patient better comprehend their diagnosis and treatment plan. The MRI is considered the most sensitive study for visualizing soft tissue structures in the spine, offering exceptional detail for assessing conditions that affect the spinal column.
Essential Cervical Spine Anatomy
The cervical spine, or neck, consists of seven stacked bones labeled C1 through C7. These vertebrae are smaller than those in the rest of the spine and provide support for the head’s weight, allowing for a wide range of motion. The first two vertebrae, the atlas (C1) and the axis (C2), have unique shapes that facilitate head movement.
Between each vertebral body is an intervertebral disc, which acts as a shock absorber. Each disc is composed of a tough outer layer, the annulus fibrosus, and a soft, gel-like inner core, the nucleus pulposus. The spinal cord, an extension of the brain, runs through the central canal, a protective tunnel formed by the stacked vertebrae.
At each level, spinal nerves branch off the spinal cord and exit the spinal canal through openings called neural foramina. These nerve roots carry signals controlling sensation and movement in the neck, shoulders, and arms. The facet joints, located at the back of the vertebrae, connect the bones and guide the spine’s motion.
Understanding MRI Image Contrast and Viewing Planes
Interpreting a cervical spine MRI requires understanding how the images are presented, which is determined by the “weighting” and the “plane” of the scan. Image contrast is managed by two common sequences: T1-weighted and T2-weighted images. These sequences use different timing parameters to highlight distinct tissue properties.
T1-Weighted Images
T1-weighted images are used for anatomical detail, showing a clear outline of structures. On these images, fat appears bright (hyperintense), while fluid, such as cerebrospinal fluid (CSF) surrounding the spinal cord, appears dark (hypointense).
T2-Weighted Images
T2-weighted images are better for detecting pathology because areas with high water content, like inflammation or edema, appear bright. On T2-weighted images, the CSF surrounding the spinal cord is bright, creating a stark contrast against the spinal cord itself. This bright fluid signal makes it easier to visualize compression or impingement caused by surrounding structures.
MRI scans present the anatomy in various orientations, known as viewing planes, to provide a three-dimensional understanding of the spine.
Viewing Planes
The sagittal plane offers a side view of the neck, dividing the body into left and right halves. This view is useful for assessing the height of the intervertebral discs and the overall alignment of the spine. The axial plane presents a cross-sectional view, crucial for visualizing the spinal canal and the nerve roots as they exit the foramina. A third plane, the coronal view, divides the body into front and back sections, but the sagittal and axial views are the most frequently used.
Interpreting Common Pathological Findings
The most frequent findings on a cervical spine MRI relate to changes in the intervertebral discs and the resulting narrowing of the spinal channels.
Degenerative Disc Disease
Degenerative disc disease begins with the loss of water content (desiccation) in the nucleus pulposus, causing the disc to lose its bright signal on T2-weighted images and appear darker. This dehydration is often accompanied by reduced disc height and the formation of bony overgrowths, called osteophytes.
Disc Herniation
Disc herniation occurs when the nucleus pulposus pushes through or beyond the outer annulus fibrosus. This displacement can manifest as a bulge (generalized extension) or a protrusion/extrusion (focal displacement), often compressing a nearby nerve root or the spinal cord. On an axial T2-weighted image, a herniated disc appears as intermediate signal material pushing into the bright CSF space.
Spinal Stenosis
Spinal stenosis describes the narrowing of the bony openings, occurring in the central canal or the neural foramina. Central canal stenosis narrows the space containing the spinal cord, often caused by disc material, thickened ligaments, and facet joint arthritis. This is visualized on a T2-weighted sagittal image as a reduction of the bright CSF signal around the spinal cord.
Foraminal stenosis is the narrowing of the neural foramen, the tunnel through which a nerve root exits the spine. This narrowing is often caused by disc material or bony spurs, constricting the nerve root’s space. Other findings, such as inflammation or edema within the bone marrow, appear bright on T2-weighted images, indicating conditions like infection, tumor, or acute injury.