Magnetic Resonance Imaging (MRI) of the thoracic spine provides detailed cross-sectional pictures of the mid-back region. The thoracic spine consists of twelve vertebrae (T1 through T12), spanning from the base of the neck to the bottom of the rib cage. This section is relatively stiff and stable because each vertebra connects to a pair of ribs. MRI uses powerful magnetic fields and radio waves to generate these detailed images without relying on ionizing radiation like X-rays or Computed Tomography (CT) scans.
Anatomy of the Thoracic Spine and MRI Visualization
The advantage of MRI is its ability to differentiate between soft tissues, a limitation for other imaging modalities. The scan provides clear visualization of the spinal cord, which is housed within the vertebral canal. The spinal cord is vulnerable in the thoracic region due to the canal’s relatively small diameter. High-resolution images allow radiologists to examine the spinal cord’s contour and signal intensity for signs of injury or disease.
The intervertebral discs, which cushion the vertebrae, are also clearly depicted. MRI assesses the hydration level and integrity of the disc’s fibrous outer ring and its gel-like center. The vertebral bodies, the thick, cylindrical front sections of the vertebrae, are visible, allowing evaluation of the bone marrow within. Surrounding soft tissues, including ligaments, muscles, and nerve roots branching off the spinal cord, are also captured.
Indications: Why a Thoracic MRI is Ordered
A physician typically orders a thoracic MRI when a patient presents with persistent symptoms that do not improve with conservative care, or when a serious underlying condition is suspected. This includes chronic, unexplained mid-back pain that may be non-mechanical, such as pain that wakes a patient from sleep. Neurological symptoms are a prompt for an MRI, as they suggest possible spinal cord involvement.
Neurological deficits can manifest as numbness, tingling, or weakness in the legs, difficulty with gait or balance, or changes in bowel or bladder function. The scan is also utilized following blunt trauma to the back to assess for spinal cord injury or unstable fractures. An MRI is often ordered when laboratory tests or other imaging suggests infection or malignant disease.
Key Pathologies Identified by the Scan
Spinal Cord Compression and Myelopathy
The thoracic spine is vulnerable to spinal cord injury due to its limited space. MRI is the definitive tool for diagnosing myelopathy, which is injury resulting from severe cord compression. The scan reveals any deformation or narrowing of the spinal cord caused by external factors like bone spurs or disc material. Increased signal intensity within the cord on T2-weighted images suggests edema (swelling) and potentially ischemia, indicating acute compromise that often requires urgent intervention.
Spinal Tumors
The spine is the most frequent site for metastatic cancer, and the thoracic region is the most common spinal location for these lesions. MRI is effective in identifying both primary and metastatic tumors that may involve the vertebral body or extend into the spinal canal. Tumor tissue often appears dark on T1-weighted images because it replaces normal fatty bone marrow. Gadolinium contrast dye causes the tumor to brighten intensely, defining the extent of the soft tissue mass and its relationship to the spinal cord.
Infections (Discitis or Osteomyelitis)
MRI is the preferred method for diagnosing spinal infections like discitis (disc infection) and osteomyelitis (vertebral bone infection) due to its sensitivity to inflammation. In cases of infection, the intervertebral disc and adjacent vertebral endplates appear bright on T2-weighted sequences due to fluid and inflammatory changes. After contrast administration, the infected disc and bone marrow show enhancement. The scan can also detect associated fluid collections, such as an epidural abscess, which may compress the spinal cord.
Disc Issues
Thoracic disc herniations are less common than those in the neck or lower back, but they are significant due to the narrowness of the spinal canal. These herniations are often central, protruding directly toward the spinal cord and potentially causing myelopathy. MRI shows the disc material extending into the canal and the resulting pressure on the spinal cord. A high percentage of thoracic disc herniations are found to be calcified, a characteristic visible on the scan.
Vertebral Fractures
The scan evaluates vertebral compression fractures, commonly caused by osteoporosis or trauma. A role of the MRI is to determine the age of the fracture and rule out malignancy. An acute (recent) fracture is identified by bone marrow edema, which presents as a bright signal on fluid-sensitive sequences. Malignant fractures, in contrast to benign osteoporotic fractures, may show abnormal signal intensity throughout the vertebral body, often involving the posterior bony elements or demonstrating an associated soft tissue mass.
Preparing for the Thoracic MRI
Preparation for a thoracic MRI requires strict attention to safety due to the powerful magnetic field. Patients must remove all metallic objects, including jewelry, watches, hearing aids, and clothing with metal zippers or snaps, before entering the scan room. It is necessary to inform the staff about any internal metallic implants, such as pacemakers, certain aneurysm clips, or neurostimulators, as some are incompatible with the magnetic field.
In some cases, Gadolinium contrast agent is injected intravenously during the procedure. This dye enhances the visibility of abnormal tissues, such as tumors or areas of inflammation, by making them appear brighter on the images. The patient lies on a movable table that slides into the cylindrical scanner. A thoracic MRI typically takes between 30 and 45 minutes, and the patient must remain completely still to ensure clear images.