A thoracic spine Magnetic Resonance Imaging (MRI) is a non-invasive diagnostic test that uses a strong magnetic field and radio waves to create detailed pictures of the mid-back region. This section of the spine, spanning from the neck base to the lower back, is often less mobile than the cervical or lumbar regions, but issues here can lead to significant pain or neurological symptoms. A healthcare provider typically orders this scan when investigating persistent mid-back pain, unexplained numbness, or potential injury to the spinal cord. The MRI provides a much clearer view of soft tissues—such as the spinal cord and intervertebral discs—than standard X-rays or CT scans, which primarily highlight bone structures.
Understanding Thoracic Spine Anatomy
The thoracic spine is composed of twelve stacked vertebrae (T1 through T12), which provide stability and anchor the rib cage. These bony blocks are separated by intervertebral discs, which act as shock absorbers. Each disc has a dense outer ring (annulus fibrosus) and a soft, jelly-like center (nucleus pulposus).
The most critical structure is the spinal cord, which runs through the center of the vertebral column, enclosed by the bony spinal canal. On an MRI, the spinal cord is surrounded by cerebrospinal fluid (CSF), which appears as a bright signal on certain sequences. The spinal cord transmits signals for the central nervous system.
The discs and vertebral bodies protect this neural tissue. The spinal cord extends down to about the T12 or L1 vertebra before transitioning into individual nerve roots. Assessing the alignment and spacing of the vertebral bodies is foundational to determining the health of the entire spinal unit.
Key Technical Elements of MRI Imaging
The interpretation of a thoracic spine MRI relies on understanding image contrast, primarily determined by T1-weighted and T2-weighted sequences. These sequences differentiate tissues based on how quickly their protons return to equilibrium after being energized. T1-weighted images (T1) are excellent for visualizing normal anatomy because fat appears bright (hyperintense) and fluid, such as CSF, appears dark (hypointense).
T2-weighted images (T2) are used for pathology because both water and fat appear bright. This brightness makes T2 images effective for identifying inflammation, edema, or infection, as these conditions involve increased water content. For instance, the bright cerebrospinal fluid (CSF) surrounding the spinal cord on a T2 image helps spot compression or displacement of the darker spinal cord.
Images are acquired in different planes, most commonly sagittal (side view) and axial (cross-sectional view). The sagittal view assesses overall curvature and alignment, while axial slices examine the spinal canal’s cross-section for narrowing or compression. Sometimes, a Gadolinium contrast agent is injected intravenously; this highlights areas with increased blood flow, such as tumors or infections, making them appear bright on post-contrast T1 images.
A Step-by-Step Approach to Viewing the Images
The methodical review of a thoracic spine MRI begins with a global assessment of alignment on the sagittal T2 images. The thoracic spine normally exhibits a smooth, gentle outward curvature (kyphosis). The reader should look for any abrupt angulation, translation (slippage), or loss of this normal curve. Checking the continuity of the anterior and posterior vertebral body lines helps confirm proper alignment.
The next step is a detailed assessment of the vertebral bodies, particularly on T1-weighted images, where healthy fatty marrow appears bright. Abnormal darkness (hypointensity) on T1, especially if accompanied by brightness on T2 (hyperintensity), suggests pathology like a compression fracture with edema, a tumor, or an infection. Compare the height of each vertebral body to its neighbors to identify collapse or wedging, which are signs of a fracture.
Following the bone assessment, evaluate the intervertebral disc spaces, primarily on T2-weighted images. A healthy, well-hydrated nucleus pulposus appears bright. Degenerative changes are seen as a loss of this bright signal (desiccation) and a reduction in disc height. Inspect carefully for any disc material extending beyond the normal confines, known as a disc protrusion or herniation.
The final focus is the spinal cord and the surrounding CSF within the spinal canal, best seen on sagittal and axial T2 views. The cord should maintain a uniform, intermediate signal intensity and have a smooth contour. Any focal area of increased signal within the cord may indicate myelomalacia (spinal cord softening) or edema, which is a sign of cord compression. Confirm that the spinal canal and the neural foramina (openings where nerves exit) are not narrowed by bone spurs, disc material, or thickened ligaments.
Identifying Specific Findings
A common finding is a disc herniation, which appears on T2-weighted images as a focal bulge or extrusion of the brighter disc material into the darker spinal canal. If the herniated material presses directly on the spinal cord, it may cause a signal change within the cord itself, appearing as a bright spot on T2, indicating edema or injury. Thoracic disc herniations are relatively uncommon but can have significant consequences due to the narrowness of the spinal canal.
Spinal stenosis, a narrowing of the spinal canal, is identified when the space available for the spinal cord is visibly reduced. This is often due to a combination of disc bulges, thickened ligaments, or bone spurs. On axial images, this narrowing shows the spinal cord tightly encompassed, with minimal or no surrounding bright CSF signal. This loss of the CSF halo is a strong indicator of significant compression.
Vertebral compression fractures are seen as a loss of height in the vertebral body, presenting as a wedge shape. On T2 images, a recent or acute fracture shows a bright signal within the fractured bone marrow, indicating bone edema or bleeding. This bright signal helps distinguish a new fracture from an older, healed one, which typically shows a dark signal on T2, similar to normal bone.