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Role of magnetic resonance imaging in acute spinal trauma: a pictorial review
© The Author(s). 2016
Received: 21 April 2016
Accepted: 12 July 2016
Published: 22 July 2016
Magnetic resonance imaging (MRI) has been playing an increasingly important role in the spinal trauma patients due to high sensitivity for detection of acute soft tissue and cord injuries. More and more patients are undergoing MRI for spinal trauma in the emergency settings, thus necessitating the interpreting physicians to be familiar with MRI findings in spinal trauma. In this pictorial review, we will first describe the normal anatomy of various ligamentous structures. Indications of MRI in spinal trauma as well as the role of MRI in diagnosing spinal cord and soft tissue injuries will then be discussed. Illustrated cases are mainly of cervical spine trauma, but thoracolumbar spine injuries are also included where appropriate in our review.
Role of MRI for evaluation of various acute traumatic spinal injuries
Role of MRI
• Higher sensitivity for detection compared to CT.
• Complete tear (seen as discontinuity of ligaments) or partial tear (seen as abnormal signal) can be differentiated.
• Helpful in guiding management by differentiating stable from unstable injuries.
Disc damages and herniations
• Detection of abnormal disc signal related to traumatic herniations.
• Important to diagnose this before closed reduction as undetected disc herniations can cause worsening cord injury.
Extra medullary hemorrhage
• MRI shows extent of hematoma to help in surgical planning.
• Extradural hematoma is commonly encountered and can lead to cord compression.
• Enable detection of arterial injuries, which include an intimal flap, pseudoaneurysm, complete occlusion or active extravasation.
• Undetected vascular injuries can cause spinal cord infarctions.
• Detection of hemorrhagic and non-hemorrhagic cord injuries.
• This is the single most important role of MRI in spinal trauma evaluation.
• Visualized as abnormal cord signal with hemorrhage best seen on gradient recalled echo (GRE) type sequences.
• Presence of hemorrhage is the most important poor prognostic factor.
Acute vs old vertebral fracture
• Age-indeterminate fractures identified on radiography and CT can be classified into acute and old fractures based on the presence or absence of bone marrow edema, respectively.
Benign vs malignant fracture
• Differentiation of benign and malignant fractures.
• Benign fractures show horizontal band of marrow edema, concave appearance of posterior vertebral margin and lack of soft tissue mass.
• Malignant fractures show almost complete involvement of vertebral body, convex posterior margin and associated soft tissue mass.
Indications of spinal MRI
Radiographic and/or CT scan findings suggestive of ligamentous injury, such as prevertebral hematoma, spondylolisthesis, asymmetric disc space widening, facet joint widening or dislocations, and inter-spinous space widening.
To look for epidural hematoma or disc herniation before attempting a closed reduction of cervical facet dislocations.
To identify spinal cord abnormalities in patients with impaired neurological status.
To exclude clinically suspected ligamentous or occult bony injuries in patients with negative radiographs.
To determine the stability of the cervical spine and assess the need for cervical collar in obtunded trauma patients.
To differentiate between hemorrhagic and non-hemorrhagic spinal cord injuries for the prognostic significance as the presence of hemorrhage significantly worsens the final clinical outcome.
National Emergency X-Radiography Utilization Study (NEXUS) or Canadian Cervical-Spine Rule (CCR) criteria are met and there are clinical findings of myelopathy.
NEXUS or CCR criteria are met and there are clinical or imaging findings to suggest ligamentous injury.
NEXUS or CCR criteria indicate imaging and the mechanically unstable spine is anticipated.
Technical Considerations for MRI
The typical MRI protocol for spinal injury includes sagittal T1 weighted (T1W) and T2 weighted (T2W) spin echo sequences, and T2* weighted (T2*W) gradient recalled echo (GRE) sequence, and sagittal short tau inversion recovery (STIR) sequences, as well as axial T2W and T2*W GRE sequences. T1W images are mainly used for depiction of anatomy and osseous fractures. STIR images are very sensitive for detection of edema and is helpful in diagnosing the soft tissue and ligamentous injuries, particularly of the interspinous or supraspinous ligaments. Although fat-suppressed T2W images can also be used for detection of edema, STIR images provide more uniform fat suppression. T2W images are very good in detecting the cord edema, and T2*W GRE images are used to detect the hemorrhage in and around the cord . Recently, diffusion tensor imaging (DTI) has been used to detect trauma related changes in the spinal cord which are not seen on conventional MRI technique [7, 8]. Ideally MRI should be performed within 72 hours of injury as the T2 hyperintensity produced by edema improves the conspicuity of the ligaments which are seen as low signal intensity in normal state . Later on, resolution of the edema and hemorrhage reduces sensitivity of MRI to detect ligamentous injuries.
Normal anatomy of the spine
The spine mainly consists of vertebrae stabilized by multiple ligaments including the anterior longitudinal ligament (ALL), posterior longitudinal ligament (PLL), ligamentum flavum, interspinous ligament, supraspinous ligament, and the apophyseal joint capsules . Anatomy of the craniocervical junction is different from the rest of the spine and consists of many ligaments. However, only tectorial membrane, the transverse ligament, and the alar ligaments act as major stabilizers. While normal tectorial membrane and transverse ligament can be easily visualized on MRI, due to lack of contrast from adjacent tissues, the normal alar ligaments are difficult to be visualized .
Three-column concept of spinal stability
Based on biomechanical studies, the vertebral column can be divided into three vertical parallel columns (i.e. anterior, middle and posterior columns) according to the Denis classification for the purposes of evaluating stability . Spinal injury is usually classified as unstable when two contiguous columns are affected. The anterior column consists of ALL, anterior two-thirds of the vertebral body and anterior two-thirds of the intervertebral disc. The middle column consists of posterior one-third of the vertebral body, posterior one-third of the intervertebral disc, and PLL. The posterior column consists of everything posterior to the PLL including pedicles, facet joints and articular processes, ligamentum flavum, neural arch and interconnecting ligaments .
Stable vs. unstable spinal injuries
Types and mechanisms of ligamentous injury
ALL is the main stabilizing ligament of the anterior column and seen as hypointense line anterior to vertebral bodies. An ALL injury appears as focal disruption of the hypointense signal on all the sequences with associated prevertebral edema best identified on STIR images. Normally PLL is seen as a hypointense line posterior to vertebral bodies. Similar to ALL injuries, injuries to PLL also appears as focal discontinuity of the hypointense line . Both ALL and PLL are better identified when elevated from the normal attachments by intervertebral discs, fluid or the bones. Ligamentum flavum is seen to connect the lamina, best identified on the parasagittal images. Injury of the ligamentum flavum is usually associated with posterior element fractures and seen as focal discontinuity. Interspinous and supraspinous ligament injuries are characterized by increased signal in the interspinous spaces and tip of the spinous processes, respectively, on STIR images. Partial tears or sprain of these ligaments are more common than complete tears. Injuries to the facet joint capsule are seen as widening of the facet joint with increased fluid signal between the joint surfaces. Since ligaments are essential components of spinal columns, the presence of their injury can change a single column injury to a two column injury, thus upgrading a stable injury to an unstable injury .
The Spine Trauma Study Group developed another scoring and classification system named ‘The Thoracolumbar Injury Classification and Severity Score (TLICS).’ This newer system was devised based on three injury characteristics: radiographic injury morphology, integrity of the posterior ligamentous complex (PLC), and neurologic status of the patient, to provide an overall severity score, enabling stratification of patients into surgical and nonsurgical treatment groups .
Acute traumatic disc herniation
Extra medullary hemorrhage and fluid collections
Spinal cord injuries
Other osseous and soft tissue injuries
Old vs acute vertebral fracture
Benign osteoporotic fracture vs malignant fracture
Pitfalls of MRI
In conclusion, MRI is more sensitive than other imaging modalities in the diagnosis of soft tissue and spinal cord injuries. While CT is considered adequate for determination of stable vs unstable spinal injuries, MRI can offer additional help due to its ability to better diagnose ligamentous injuries when compared with CT. MRI is also helpful in predicting the prognosis by demonstrating the hemorrhagic and non hemorrhagic cord injuries.
ACR, American College of Radiology; ALL, Anterior Longitudinal Ligament; CCR, Canadian Cervical-Spine Rule; CT, Computed tomography; DTI, Diffusion Tensor Imaging; GRE, Gradient Recalled Echo; MRI, Magnetic Resonance Imaging; NEXUS, National Emergency X-Radiography Utilization Study; PLC, Posterior Ligamentous Complex; PLL, Posterior Longitudinal Ligament; STIR, Short Tau Inversion Recovery; TE, Echo Time; TLICS, Thoracolumbar Injury Classification and Severity Score
Availability of data and materials
All authors made the following contribution in preparation of this paper. Made substantial contributions to conception and design, or acquisition of data, or analysis and interpretation of data; Been involved in drafting the manuscript or revising it critically for important intellectual content; Given final approval of the version to be published. Each author should have participated sufficiently in the work to take public responsibility for appropriate portions of the content; and Agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.
Both authors have nothing to disclose.
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