Imaging of spine trauma

Transcription

1 Imaging of spine trauma RD Magazine, 44, 514, Dr Matthew Jaring Speciality registrar in clinical radiology Dr Roland Watura onsultant musculoskeletal radiologist Southmead Hospital, ristol Introduction The majority of spinal cord injuries are the result of preventable causes such as road traffic accidents, falls or violent acts. 1 Trauma to the spinal column and spinal cord can lead to potentially devastating injuries and long-term or permanent disability. Prompt and appropriate imaging is therefore vital for the diagnosis, assessment and management of spine injuries. The imaging is required to demonstrate the sites of injury, assess spine stability and to demonstrate any damage to the cord and other neural structures. 2 Major trauma centres have been established in the UK to provide centralised and specialist care of patients who have suffered serious injuries. nalysis of data from these centres has found that almost 24% of trauma patients will suffer a spinal fracture. 3 Timely imaging of trauma patients as well as prompt and accurate image interpretation is vital, as a missed diagnosis of a spinal fracture increases the risk of secondary neurological injury tenfold. 4 In this article we discuss mechanisms of spine injury and the role of imaging in spine trauma. Mechanisms of spine injury and assessment of spine stability Spinal injuries may occur as a result of various mechanisms and forces acting on the spinal column. These include: 1, xial loading, which may cause burst or wedge compression fractures. 2, Hyperflexion injuries that can result in compression fractures, particularly to the anterior column, or more severe injuries such as the flexion teardrop fracture with disruption of the posterior supporting structures and the intervertebral disc. 3, Hyperextension injuries resulting in disruption of the anterior supporting structures such as the anterior longitudinal ligament. These may also result in the hyperextension teardrop fracture and disruption of the intervertebral disc. 4, Rotation injuries may result in facet subluxation or dislocation. Spinal injuries may result from a combination of these forces. 3 White and Panjabi (1978) defined clinical stability of the spine as follows: The ability of the spine under physiologic loads to limit patterns of displacement so as not to damage or irritate the spinal cord or nerve roots and, in addition, to prevent incapacitating deformity or pain due to structural changes. ny disruption of the spinal components (ligaments, discs, facets) holding the spine together will decrease the clinical stability of the spine. When the spine loses enough of these components to prevent it from adequately providing the mechanical functions of protection, measures are taken to re-establish the stability. 5,6 Various classifications have been devised in order to aid in the image assessment of spinal stability. Detailed discussion of these is not within the scope of this article but the most well-known is the three-column theory of Denis. 7 This divides the spine into three columns: n anterior column including the two anterior thirds of the vertebral body and discs, a middle column consisting of the posterior third of the vertebral body and discs, and a posterior column consisting of the facet joints, lamina, spinous processes and intricate ligamentous complex. Disruption of two or more of these is considered unstable. This theory does not apply to injuries at the craniocervical junction, above 3. The role of imaging in the diagnosis and evaluation of spine trauma The Joint Section on Disorders of the Spine and Peripheral Nerve has made recommendations with regard to the role of imaging of patients with acute injury to the cervical spine and spinal cord. 8 For the patient who is asymptomatic and alert, does not have neck pain or distracting injury, is able to perform a functional range of movements and whose neurological examination is normal, clinical clearance is all that is required. Radiographic imaging and evaluation is not recommended. For the patient who has neck tenderness and pain, multi-detector computed tomography (MDT) is recommended. If no fractures are identified on MDT, further imaging with magnetic resonance imaging (MRI) may be considered, particularly if there are neurological signs present or deteriorating, or there is deformity or pain. Flexion and extension views have high false positive and false negative rates and are therefore not recommended. 2,9 Dynamic fluoroscopy is also not recommended as it does not identify any fractures or instability that are not visualised by MDT. 10 MRI is also recommended for patients with suspected spinal cord injury. It can locate the injured anatomical sites and demonstrate various causes of spinal cord compression such as fractures, haematomas or traumatic disc protrusions. MDT and MRI are the main imaging modalities for the evaluation of traumatic spinal injury. The sensitivity of MDT for spinal trauma imaging is estimated at %. In comparison, plain radiographs underestimate the extent of spinal injuries. Radiographs of the cervical spine only detect 43-80% of cervical fractures and it is frequently not possible to view the whole cervical spine, even when additional views such as open mouth and swimmer s views are obtained. 2,3,9-13 MDT is the fastest imaging technique for spine trauma assessment. It demonstrates bony anatomy in high spatial resolution. Thin section axial data sets can be acquired and reformatted in multiple planes. lgorithms are available for optimal visualisation and evaluation of bone and soft tissues. MDT also detects haematomas in the paravertebral soft tissues, epidural and subdural haematomas as well as signs of subcutaneous soft tissue injury. Polytrauma protocols that include reconstruction of images of the spine from MDT of the chest and abdomen are followed in major trauma centres. These protocols help to reduce radiation exposure. Sensitivity and specificity of these protocols for detection of spinal fractures is reported to be 97-98%. 14 t our institution all data is derived from two separate acquisitions on a 64- slice MDT scanner, the first being a non-contrast acquisition of the head and cervical spine and the second being a biphasic split bolus acquisition of the chest, abdomen and pelvis. In addition to soft tissue and lung kernels, bone kernels are applied to axial 0.625mm thickness slices of the neck, chest, abdomen and pelvis. This allows near-lossless multiplanar reconstruction on dedicated PS workstations immediately following imaging. In order to facilitate rapid assessment of injuries in both the emergency department and theatres, axial, coronal and sagittal reconstructions are provided (2mm thickness for the cervical spine and 3mm thickness for the thoracolumbar spine). lthough MDT is now the primary imaging modality for evaluating patients

2 with injury to the spine, a drawback is its inability to visualise the cord, ligaments and soft tissue detail. 2,10,15 MRI complements MDT in the assessment of spine trauma as it is the best available imaging modality for evaluating soft tissues. It is highly sensitive for demonstrating the cord, epidural haematomas, intervertebral discs and the ligamentous structures, all of which are not as well visualised by MDT. When required, MRI is normally carried out after trauma patients have been assessed by MDT. Various MRI imaging protocols can be employed to optimise tissue characterisation and image resolution. In acute trauma, the standard protocols include sagittal T1 and T2 sequences as well as short-tau inversion recovery (STIR) sequences and T2 or T2* axials. T2 or STIR sequences highlight cord and disc abnormalities and are sensitive to oedema and collections such as haematomas in and around ligamentous structures, and within bone marrow. Posterior ligamentous complex structures are increasingly being recognised as important for stability of the spine. Injury to these structures is well demonstrated on T2-weighted sagittal scans with a high degree of sensitivity and specificity. 16 Gradient echo (T2*) images are not routinely used but may be more sensitive to haemorrhage in the cord and soft tissues. 17 For that reason, sagittal T2* images may improve visualisation of cord haemorrhage where this is required. Recent studies have shown that susceptibility-weighted sequences are now more sensitive than gradient echo for detecting haemorrhage in acute spinal cord injury. 2,18 lthough MRI is used for diagnosis of spinal cord and soft tissue injury as follow-up to abnormal finding at MDT, it is also useful for demonstration of injuries in patients who have had a normal MDT examination but where there remains a high index of suspicion of injury. 15 MRI sensitivity for injury to the disc and ligamentous structures was shown in one study to range from 93 to 100%, but limited correlation with findings at surgery led the authors to conclude that MRI overestimated the extent of ligamentous disruption. 19 ccording to rinckman et al, only fractures resulting from vertebral body compression reliably generate marrow oedema. Fractures without compression or resulting from distraction may therefore be under-diagnosed at MRI due to lack of oedema. 20 MRI also better demonstrates paraspinal haematoma and epidural haematoma posterior to the cord. The MRI appearance of a haematoma depends on the oxidative state of the haemorrhage. In the hyperacute (<24h) phase, haematoma is isointense-bright on T2/STIR images and isointense with the spinal cord on T1-weighted images. This can result in difficulty detecting haematoma, and changes over the course of injury (acute (1-2d): T1 isointense, T2/STIR dark; early subacute (3-7d): T1 bright, T2/STIR dark; late subacute (7-28d) T1/T2/STIR bright; chronic (>28d) T1/T2/STIR dark). The role of MRI for clearance of the cervical spine in the unconscious or obtunded patient who has suffered blunt trauma remains a subject of debate. Several studies have now been published supporting one or the other side of the debate. Some studies have concluded that MRI is unlikely to uncover unstable cervical spine injuries in 11, 21 obtunded/comatose patients with negative MDT scans. In these two studies, none of the patients had a missed unstable injury, and no patient required surgery or developed evidence of instability. 2 Two meta-analyses looking at the role of MRI for cervical spine clearance following blunt trauma, however, came to a different conclusion. They concluded that not carrying out MRI in patients with suspected cervical spine injury, or with unreliable clinical examinations and negative MDT, could result in missed injuries. They also state the advantage of MRI for being able to conclusively exclude cervical spine injury. 22,23 onclusion Multi-detector T has become the primary method for imaging in acute spinal trauma. The rapid acquisition, often as part of a trauma protocol, has a sensitivity approaching 100% for fracture, and has rendered the plain radiograph (especially in the cervical spine) obsolete in all but the most innocuous of injuries. MDT, however, does have limitations in assessing soft tissues, ligaments and the spinal cord, including assessing epidural haematoma, which are complemented by the availability of MRI in well-selected cases. The process of MRI is considerably more difficult, especially in the unstable patient. Reasons to proceed to MRI include cases where the clinical examination suggests spinal pathology despite normal T, in obtunded patients where examination is unreliable, and circumstances where there is radiological and clinical suspicion for spinal cord injury. References 1, No 384 Spinal ord Injury. World Health Organization; vailable from: 2, Shah L M, Ross J S. Imaging of spine trauma. Neurosurgery 2016;79(5): , Purohit N, Skiadas V, Sampson M. Imaging features of spinal trauma: What the radiologist needs to know. lin Radiol 2015;70(5): , Reid D, Henderson R, Saboe L, Miller J. Etiology and clinical course of missed spine fractures. J Trauma cute are Surg 1987;27(9): , White, Panjabi M M. linical iomechanics of the Spine: Lippincott; , ergmark. Stability of the lumbar spine: study in mechanical engineering. cta Orthopaedica Scandinavica 1989;60(suppl 230): , Denis F. The three column spine and its significance in the classification of acute thoracolumbar spinal injuries. Spine 1983;8(8): , Hadley M N, Walters. Introduction to the guidelines for the management of acute cervical spine and spinal cord injuries. Neurosurg 2013;72(suppl 3): , Harris T J, lackmore, Mirza S K, Jurkovich G J. learing the cervical spine in obtunded patients. Spine 2008;33(14): , Padayachee L, ooper D J, Irons S et al. ervical spine clearance in unconscious traumatic brain injury patients: Dynamic flexion-extension fluoroscopy versus computed tomography with three-dimensional reconstruction. J Trauma cute are Surg 2006;60(2): , Tomycz N D, hew G, hang Y-F et al. MRI is unnecessary to clear the cervical spine in obtunded/comatose trauma patients: The four-year experience of a level I trauma center. J Trauma cute are Surg 2008;64(5): , Nuñez D, hmad, oin G et al. learing the cervical spine in multiple trauma victims: time-effective protocol using helical computed tomography. Emerg Radiol 1994;1(6): , Holmes J F, kkinepalli R. omputed tomography versus plain radiography to screen for cervical spine injury: meta-analysis. J Trauma cute are Surg 2005;58(5): , Roos J E, Hilfiker P, Platz et al. MDT in emergency radiology: Is a standardized chest or abdominal protocol sufficient for evaluation of thoracic and lumbar spine trauma? m J Roentgenol 2004;183(4): , Utz M, Khan S, O onnor D, Meyers S. MDT and MRI evaluation of cervical spine trauma. Insights Imaging. 2014;5(1): , Lee H-M, Kim H-S, Kim D-J et al. Reliability of magnetic resonance imaging in detecting posterior ligament complex injury in thoracolumbar spinal fractures. Spine 2000;25(16): , Katz H, Quencer R M, Hinks R S. omparison of gradient-recalled-echo and T2-weighted spin-echo pulse sequences in intramedullary spinal lesions. m J Neuroradiol 1989;10(4): , Wang M, Dai Y, Han Y et al. Susceptibility weighted imaging in detecting hemorrhage in acute cervical spinal cord injury. Magn Reson Imaging 2011;29(3): , Goradia D, Linnau K, ohen W et al. orrelation of MR imaging findings with intraoperative findings after cervical spine trauma. m J Neuroradiol 2007;28(2): , rinckman M, hau, Ross J S. Marrow edema variability in acute spine fractures. Spine J 2015;15(3): , Hogan G J, Mirvis S E, Shanmuganathan K, Scalea T M. Exclusion of unstable cervical spine injury in obtunded patients with blunt trauma: Is MR imaging needed when multi-detector row T findings are normal? Radiol 2005;237(1): , Muchow R D, Resnick D K, bdel M P et al. Magnetic resonance imaging (MRI) in the clearance of the cervical spine in blunt trauma: a meta-analysis. J Trauma cute are Surg 2008;64(1): , Schoenfeld J, ono M, McGuire K J et al. omputed tomography alone versus computed tomography and magnetic resonance imaging in the identification of occult injuries to the cervical spine: meta-analysis. J Trauma cute are Surg 2010;68(1):

3 Figure 1 () coronal MDT, () axial MDT and () sagittal MRI with fat suppression. 82-year-old female patient who slipped on a carpet and sustained a neck injury. The T scan and MRI demonstrate a fracture across the base of the dens. The dens fracture is associated with fractures of 1 (Jefferson fracture). Note the prevertebral haemorrhage and also haemorrhage in the posterior soft tissues on the MRI scan. This is a type II dens fracture and is unstable. Incidence of non-union of these fractures is between 30% and 50%. Type III dens fractures occur through the body of the dens and can also be unstable. Type I dens fractures, on the other hand, occur at the tip of the dens (alar ligament insertion) and are considered stable. Figure 2 () sagittal MDT, () axial MDT and () sagittal MRI with fat suppression. 20-year-old patient injured while tombstoning. The imaging demonstrates a flexion teardrop fracture of 5. This is a severe hyperflexion injury. Profound neurological deficit is common with signs and symptoms of acute anterior cord syndrome. The MDT ( and ) shows fracture, anterior wedging and reduced height of the 5 vertebra as well as a large separated teardrop fragment anteriorly. MRI scan (T2 sagittal image) () demonstrates oedema within the vertebral body. Note also the signal hyperintensity within the cervical cord at this level indicating cord injury. This is a result of the vertebra being driven posteriorly into the cord during hyperflexion. ll the anterior and posterior ligaments are disrupted. MRI is limited in its ability to detect non-displaced fractures through the vertebral bodies and the posterior elements, particularly in the cervical spine, but MDT shows the fractures clearly.

4 Figure 3 () sagittal MDT, () sagittal STIR MRI. 59-yearold male tetraplegic following fall from horse. MDT shows retrolisthesis of 3 on 4 and a large prevertebral haematoma. MRI shows disruption of the 3/4 intervertebral disc. There is also disruption of the anterior longitudinal ligament as well as haematoma and oedema in the posterior vertebral soft tissues. There is also signal hyperintensity within the cord consistent with cord injury and haemorrhage. Figure 4 () sagittal MDT, () sagittal STIR MRI, () axial STIR MRI, (D) sagittal T1 MRI. 47-year-old male. Fell from a horse. The sagittal MDT scan demonstrates hance fracture of T6 extending across the posterior elements with anterior D wedging and reduced height of the vertebral body as well as fracture of the posterior elements. MRI demonstrates marrow oedema not just in T6 but also in other vertebral bodies that are not obviously fractured on MDT (T4 and T7).

5 Figure 5 () lateral radiograph, () sagittal STIR MRI. 30- year-old involved in an RT. Radiograph and MRI demonstrate facet dislocation at 6/7 with anterior subluxation of 6 on 7. Note the bow tie sign of the dislocated facet on the radiograph. Facet dislocation can be unilateral or bilateral. ilateral facet joint dislocation is a severe and unstable injury. ll supporting ligaments are disrupted. There is a 60% chance of cord and peripheral nerve injury MRI shows disruption of the 6/7 intervertebral disc with disc haemorrhage and oedema associated with a traumatic posterior disc herniation. oth result in compression of the cord and canal stenosis. There is also haemorrhage in the soft tissues anterior and posterior to the spinal column indicating ligament injury or disruption. Figure 6 () sagittal MDT, () axial MDT. 28-year-old involved in an RT. This demonstrates a burst fracture of L1. There is disruption to both anterior and middle columns of the L1 vertebral body, often occurring in the setting of high energy axial loading. This unstable injury is compounded by retropulsion of a fracture fragment into the anterior spinal canal, risking potentially catastrophic traumatic spinal cord injury, as well as ongoing canal stenosis. widened interpedicular distance is often seen on axial or coronal images. In this case there is extension into the posterior elements, and MRI will often show associated posterior ligamentous injury. urst fractures are most common at L1, likely due to the change in loading between the thoracic and lumbar spine.