Role of magnetic resonance imaging in acute spinal trauma: a pictorial review
Yogesh Kumar and Dalchi Hayashi
JACO Editorial Reviewer: Deanna O’Dwyer, DC
Published: March 2017
Journal of the Academy of Chiropractic Orthopedists
March 2017, Volume 14, Issue 1
The original article copyright belongs to the original publisher. This review is available from: http//www.dcorthoacademy.com © 2017 O’Dwyer and the Academy of Chiropractic Orthopedists. This is an Open Access article which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Generally speaking, computerized tomography (CT) is the standard of care for the emergency room trauma setting, mainly due to its’ accessibility and relatively lower cost. However, the role of magnetic resonance imaging (MRI) is becoming more sophisticated and available. Compared to CT, MRI has more clear visualization of both ligaments as well as soft tissue. This is demonstrated most markedly by the visualization of the 5 cervical ligaments and their relative anatomical position. This paper speaks to cervical spine imaging and trauma.
Typically, the indications for an MRI would be:
1) Suggested ligamentous injury via radiograph or CT finding.
2) Visualize epidural hematoma or disc herniation prior to closed reduction of facet dislocation (cervical).
- Identify cause of neurologic impairment.
- Evaluate ligamentous or boney injury in “negative radiograph” patients.
- Evaluate the ligamentous and boney stability of a cervical spine trauma.
- Diagnose and predict prognosis of hemorrhagic vs. non-hemorrhagic spinal cord injury.
There are various types of MRI which have different functionality.
- T1weighted (T1W) visualizes fracture and normal v. abnormal anatomy
- T2 weighted (T2W) visualizes some fat suppression and cord edema.
- T2 gradient recall echo sequence (GRE) visualizes cord hemorrhage
- Sagittal short tau inversion recovery (STIR) visualizes soft tissue and ligamentous
damage, as well as, more uniform fat suppression than T2W.
Unfortunately, as good as MRI is, it is most diagnostic within 72 hours of ligamentous damage.
The spine consists of 5 ligaments which help to both increase stability and prevent excess movement. The anterior longitudinal ligament (ALL), posterior longitudinal ligament (PLL), ligamentum flavum, interspinous ligament, supraspinous ligament.
The cervico-occipital joint consists of extra stabilizing ligaments which differ from the rest of the spine. The only of these ligaments which can be visualized on MRI are the tectorial membrane and the transverse ligament. The alar ligament is not well visualized due to lack of contrast.
Many anatomists subscribe to the “Denis classification”. This divides the spinal column into a posterior, middle and anterior column. The posterior column is composed of all structures posterior ro the PLL. The middle column includes the posterior 1/3 of both the vertebral body and intervertebral disc and the PLL. The anterior column consists of the ALL, the anterior 2/3 of both the disc and the vertebral body.
Spinal stability is a result of whether the trauma results in more than 1 column being affected. Normally, on MRI undamaged ligaments will demonstrate low signal intensity with some high signal intensity due to normal fat visualization. Partial ligamentous tears will show high signal intensity. Complete tears will also demonstrate high signal intensity on STIR examination due to the edema and hemorrhage.
The mechanism of injury will determine the most likely structural injury (eg: hyperextension injury generally result in anterior or posterior column damage). Visualized as a hypointense line anterior to the vertebral body the ALL is the main stabilizing ligament of the anterior column. Injury results in focal disruption of the hypointense signal in all sequences. Similar results occur in injury to the PLL and the posterior column. The ligamentum flavum (recall it attaches the lamina) will demonstrate most appropriately in the sagittal STIR series. LF injuries are usually associated with posterior column fracture with focal disruption. Capsular inuries are demonstrated by widening of the facet joints.
Another scoring classification, devised by the Spine Trauma Study Group is based on 3 injury traits: injury morphology demonstrated on plain film, posterior ligament complex integrity and neurologic status. This is called the “Thoracolumbar Injury Classification and Severity Score (TLICS). This newer type of classification helps to triage patients into surgery vs. non-surgery treatment groups.
MRI is a better study of choice for disc herniations, extramedullary hemorrhage and fluid collections. MRI vs CT reveals better soft tissue resolution and hematoma visualization.
Blunt force and penetrating trauma to the neck generally involves the vertebral arteries more commonly than the carotid arteries. Less significant traumas could potentially lead to cerebral/cerebellar infarctions. Vascular injury is usually visualized as irregularity or loss of flow in T2W. If there is a question of injury to vascularity, a CT angiography could be employed.
Spinal cord injuries are classified according to the American Spinal Injury Association (ASIA) uses a A-C grading. A=Complete loss of motor and function in the sacral segments. B=Incomplete loss of sensory but not motor function below the level of the lesion to the sacral levels. C= Incomplete Motor function preserved below the level of the lesion with muscle preservation of <3/5. D=motor function preserved belothe level of the lesion with muscle intact at >/= 3/5. E=normal. In spinal cord injury axial and sagittal T1 and T2W GRE images are most diagnostic with hyperintense T2 abnormality resultant of cord edema.
Other osseous or soft tissue injury can be well visualized with MRI vs. CT. CT is hard to image when whereas MRI reveals areas of hyperintense signal demonstrating edema or hemorrhage. If the injures involve the ligaments, there is thickening of the ligament visualized on MRI.
Chronic fracture vs. acute fracture can be enhanced with MRI enhancement of the marrow. Generally, acute fracture will demonstrate more water content than a chronic fracture. Marrow edema is visualized as low intensity on T1W and high intensity on T2W and STIR images. Chronic fractures demonstrate fatty marrow high signal intensity on T1W and T2W without edema.
Osteoporotic fracture usually causes a horizontal band of abnormal signal intensity with a separation of normal fatty marrow. Metastatic fracture involves the entire vertebral body with abnormal marrow edema.
The drawback of MRI mainly involve artifacts which may result from metallic clips or dental implants, the sensitivity is lower for posterior element fracture as well as craniocervical fracture. MRI is more sensitive than other imaging modalities for soft tissue, edema, ligamentous and cord injury compared to CT. While CT is more diagnostic for osseous stable vs unstable injury.