Eur Radiol (2002) 12:1262–1272 DOI 10.1007/s00330-002-1448-5

H. Imhof M. Fuchsjäger

Published online: 20 April 2002 © Springer-Verlag 2002 Categorical Course ECR 2003 H. Imhof (✉) · M. Fuchsjäger Department of Osteology, Universitätsklinik für Radiodiagnostik, AKH, Währinger Gürtel 18–20, 1090 Vienna, Austria e-mail: [email protected] Tel.: +43-1-404005803 Fax: +43-1-404003777

EMERGENCY RADIOLOGY

Traumatic injuries: imaging of spinal injuries

Abstract Severe (high-energy) spinal injuries are common sequelae of acute traumas. The task of radiology is to establish the radiological diagnosis, classify it, judge stability and instability and lead further radiological evaluation in cases of non-agreement between the radiological diagnosis and the clinical (neurological) findings. While skeletal abnormalities are best diagnosed with spiral CT and to a lesser degree with plainfilm radiographs, soft tissue lesions,

Introduction In the European Union there are over 130,000 disabled survivors of spinal injuries per year. In a vast majority of cases their initial radiographs were taken in community hospitals. In these cases, plain-film radiography remains the foundation upon which the initial evaluation and diagnosis of spinal injuries are based. With the introduction of (multi-slice) spiral CT the basic importance of conventional radiograph decreased. Spiral CT allows the examination of the whole spine in a very short time. Excellent rapid reconstructions in any plane helps in the exact diagnosis of bony and soft tissue abnormalities. In past years emergency MRI has reached a prominent position in the diagnostic clarification of severe spinal trauma, too. It allows better demonstration of the presence, location and extent of cord lesions, ligament ruptures, disc herniation, vascular lesions and bone marrow abnormalities. This is of great importance, because the consequences of a wrong, inaccurate or incomplete diagnosis of severe spinal traumas can have life-long devastating consequences. An awareness of the strengths and limitations of radiology is fundamental in providing

such as cord injuries or ligament ruptures, are best outlined with emergency MRI. The classification of fractures depends on fracture (trauma)-biomechanics and location. All these efforts are necessary to get the best clinical outcome for the patient. Keywords Spinal trauma · Fracture classification · Imaging

the best practice. An interactive and inter-dependent approach is essential harnessing plain radiography, spiral CT and MRI in the diagnosis of vertebral bony and soft tissue injuries. Spinal cord injury occurs in 10–14% of spinal fractures and dislocations [13]. Injuries of the cervical spine are by far the ones commonly associated with neurologi-

Fig. 1 Frequency of spinal fractures in correlation with segments

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Fig. 2 The lateral cervical spine and three parallel lines: anterior longitudinal ligament; posterior longitudinal ligament; and interspino-laminar line Table 1 Systematic inspection of the images in severe spinal trauma

Fig. 3 The anteroposterior cervical spine: straight line through the spinous processes

Alignment

Subluxation/dislocation

CT and radiographs

Spinal cord

Oedema Swelling Haemorrhage Compression Dissection

+

Epidural space

Disk herniation Bone fragment Haematoma

+ + +

Spinal column

Vertebral body fracture Posterior element fracture Dislocation Bony oedema Spondylosis

+ + +

MRI + + + + + + +

+ +

Ligaments

Anterior longitudinal ligament rupture Posterior longitudinal ligament rupture Interlaminar ligament (flava) rupture Supra- or interspinous ligament rupture

+ + + +

Vascular

Vertebral artery–occlusion/dissection

+

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Table 2 Imaging protocol. SE spin echo; GRE gradient recalled echo; STIR short tau inversion recovery

Clinical situation:

Imaging procedure:

Trauma with spinal involvement (low-risk patient) Unclear bony fracture Bony fragments Facet joints Spinal canal

Plain radiographs (anteroposterior, lateral) Spiral (multi-slice) CT:

Cord injury Epidural space Vascular supply Disk herniation Ligament/muscle rupture Bone marrow oedema

MRI: T2 STIR T1 SE T2 fast SE T2* GRE T1 SE T2 fast SE

High-resolution mode

sagittal

axial

Fig. 4 a Magnetic resonance imaging of cervical spine (lateral, T2-weighted): hyperintense bleeding within the cord and prevertebral. b Magnetic resonance imaging of cervical spine (lateral, T2-weighted): hyperintensity within bone marrow of C6 and C7 and cord representing oedema

cal damage, which occurs in approximately 40% of cases [5]. In 85% of cases the spinal cord injury occurs at the time of trauma, whereas 5–10% are seen in the immediate post-injury period [14]. The highest frequency of spinal traumas are found in the lower cervical spine and cervico-thoracic junction (Fig. 1).

Injury assessment Until the beginning of the 1990s adequate plain radiographs were the initial investigation to assess bone injury and misalignment. It was reported that in approximately 50–70% of all cases plain radiographs could give the fi-

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Table 3 Radiographic findings of cervical spine instability Widened interspinous space or facet joints Anterior listhesis >3.5 mm Narrowed or widened disk space Focal angulation >11° Vertebral compression >25% Table 4 Radiographic findings of upper thoracic spine instability Fracture–dislocation Posttraumatic kyphosis >40° Spine fractures associated with sternal fractures Concomitant rib fractures and/or costovertebral dislocation Table 5 Components of the three osteoligamentous columns of the spine Column

Components

Anterior

Anterior longitudinal ligament Anterior annulus fibrosus Anterior two-thirds of the vertebral body and disk

Middle

Posterior third of the vertebral body and disk Posterior annulus fibrosus Posterior longitudinal ligament

Posterior

Pedicles, laminae Facet capsules Interlaminar ligaments (flava) Supra- or interspinous ligaments

Imaging

Table 6 Instability signs in the lower thoracic and lumbar spine Stable

Unstable

One column Two not neighbouring columns involved

Three columns Two neighbouring columns involved

Table 7 Functional classification of cervical spine fractures and dislocations

nal diagnostic answer. No further imaging would be necessary if the clinical symptoms are in agreement with the imaging findings. Various authors [2, 11, 12] proved that if one uses only conventional radiographs 23–57% of all fractures of the cervical spine are missed. This may lead optimistically to a delayed correct diagnosis, or pessimistically to a disastrous mismanagement of the patient. Due to these results, there are a lot of advocates of an emergency spiral CT as first imaging method in severe spinal trauma and/or in high-risk patients. High-risk patients are such with multiple injuries, abnormal mental status or where the injury mechanism is very suggestive of a severe spinal trauma. Only in low-risk patients can conventional radiographs be performed and trusted as a sole modality. Moreover, all problems concerning soft tissue (e.g. cord, vessel, ligament, muscle) or bone marrow should be solved with MRI. Contrary to other diagnostic problems in the human body, overdiagnosing in any questionable case should be the rule, because of the possible life-long devastating sequelae of mis(under)diagnosis. The role of imaging is threefold: to assess the spinal injury; to direct appropriate management; and to predict neurological outcome.

Anteroposterior (AP) and lateral plain radiographs should be taken without change of the patient’s position. These views should include the cervico-thoracic junction and allow to assess the three (or four) parallel longitudinal lines: on the lateral view a line joining the anterior margins of the vertebral bodies; the posterior margin of the vertebral bodies; the spinolaminar line joining the junction of the laminae with the anterior margin of spi-

Mechanism of injury

Type

Stable

Hyperflexion

Anterior subluxation (sprain) Bilateral interfacetal dislocation Simple wedge fracture Clay-shoveler’s fracture Teardrop fracture Odontoid fracture

+

Hyperextension

Vertical compression

Dislocation (sprain or strain) Avulsion fracture of the posterior arch of C1 Fracture of the posterior arch of C1 Teardrop fracture of C2 Laminar fracture Hangman’s fracture Jefferson’s fracture Burst fracture

Unstable +

+ + +

+ +

+ + + + + + + +

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Fig. 5 Magnetic resonance imaging of the cervical spine (lateral; T2-weighted): ventral subluxation of C2 on C3 with dorsal disk herniation and cord compression. Severe oedema and bleeding in the dorsal spinal parts and soft tissues

nous processes; and eventually a line joining the tips of spinous processes (Fig. 2). Of particular importance is the integrity of the posterior vertebral body line. On the AP view a line along the tips of spinous processes should be running straight downwards (Fig. 3). The dou-

ble spinous process sign seen on AP radiographs is a reliable indicator of a fracture of the spinous process. In upper thoracic spine fractures, but also cervical spine fractures, the abnormal widening of pre- or paravertebral soft tissue structures is significant. But the important “take home message” is that normal soft tissue structures do not exclude a fracture; abnormal ones are good indirect fracture signs, however [4, 6, 7, 10, 15]. If these lines, the bony margins, cancellous bone, and the neighbouring soft tissues outlined by fat or air are within normal limits, and the patient is a low-risk patient, all further examinations can be stopped. In case the patient shows an abnormal positioning of head and/or spine, repositioning for imaging is contraindicated until it is proven that the reason for the abnormal position is not due to a life-threatening/painful pathology. Bony structures, e.g. compressions, dislocations and avulsion fractures, are best seen with spiral CT. It is advisable to use a spiral (multi-slice) CT in high-resolution (HR) mode (slice thickness: 3/3 mm; reconstruction interval: 1.5 mm), which allows shortening of examination time with fewer motion artefacts and quick reformation of images in all planes. The standard axial view of CT optimizes visualization of the skeletal borders of the spinal canal, facet joints and spinous processes. Bony fragments within the spinal canal are easily demonstrated (Tables 1, 2). Basically, fracture lines are always best demonstrated if they are running at an angle of 90° to the direction of visualization. In case the patient shows a neurological deficit with or without radiological agreement, MRI of the spine is indicated. By means of MRI cord injuries (oedema, bleeding, necrosis, dissection), vascular (a. vertebralis) injuries – with an incidence rate of 15–20% – like dissections or arterial occlusions can be seen or ruled out (Fig. 4). Finally, disk herniations (CT has sensitivity of only 33%), rupture of ligaments and/or muscles, nerve root damages and bone marrow oedema can be demonstrated (Fig. 5). Open-mouth views or oblique views of the spine are no longer recommended. Instead, CT or MRI should be used. The accuracy of each modality is much higher than

Table 8 Functional classification of thoraco-lumbar spine fractures and dislocations Mechanism of injury

Type

Status

Hyperflexion with axial loading

Compression or wedge fracture

Stable (angulation <40°) 50% of all fractures

Vertical compression with minor spinal flexion

Burst fracture

Unstable/stable 17% of all fractures Cord injury in 50%

Hyperflexion with axis of rotation anteriorly within abdominal wall

“Lap-belt” fracture (with one segment: chance fracture; with more than one segment: Smith fracture)

Unstable 5% of all fractures

Flexion–rotation/flexion–distraction shear

Fracture–dislocation

Unstable 20% of all fractures 75% with neurological deficit

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Fig. 6 a Radiograph of cervical spine (lateral): flexion–teardrop fracture with minor anterior dislocation C6 in comparison with C5 and fracture of the spinous process. b Axial CT of C5: typical fracture of the vertebral body and dislocation of the facet joints. Fracture fragment on the right side of the facet joint

that of plain radiographs. Dynamic views (flexion and extension) are contraindicated in the acutely traumatized spine. They are still of some importance in the long-term follow-up of whiplash injuries. In unconscious patients with severe spinal trauma all scanning imaging modalities (spiral CT and MRI) should be used. Conventional tomography has been completely replaced by spiral CT. Myelography and CT myelography should be used only in cases where no MRI is available and in rare cases of dural sac tears or unclear nerve root problems.

Stability/instability/fracture classification

Fig. 7 Radiograph of cervical spine (lateral): anterior bilateral dislocation of the facet joints and anterior subluxation of C5 on C6

The sentence of Denis et al., “that a spine that can withstand normal physiological stresses without progressive deformity or neurological abnormalities, or both, is considered stable”, has been valid for almost 20 years [8]. After the first absolutely necessary emergency therapies, which in most cases concern spinal cord problems, nerve damages or vascular problems, the long-term survival and future living conditions of the patient depend very much on bony stability. The main signs of instability on CT or radiographs for the cervical and upper thoracic spine are explained in Tables 3 and 4. The three-column concept [8] was applied originally only in the lower thoracic and lumbar spine, but can be used in the cervical spine with some modifications, too (Tables 5, 6). This concept states that fractures affecting two or three columns or only the middle column are unstable. Accordingly, blunt trauma is classified by the anatomical location and biomechanics of injury (Tables 7, 8).

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Fig. 8 Axial CT of C5: left-sided facet joint dislocation and fracture

Special spinal injuries Hyperflexion Flexion injury of the cervical and thoraco-lumbar spine results in forward rotation or translation of the vertrebra in the sagittal plane. This injury is caused by direct trauma to the head and neck in the flexed position, or by forces that cause hyperflexion of the neutral spine. Prominent features of flexion injury are disruption of the posterior ligament complex, the interlaminar ligaments, the facet capsules and the posterior part of the annulus fibrosus. The injury is acutely stable, although the incidence of delayed instability is high varying from 20 to 50%. The clay-shoveler’s fracture with fracture of the spinous process and the simple wedge fracture tend to be stable, whereas the bilateral interfacetal dislocation and teardrop fracture are unstable fractures. They all feature disruption of the posterior ligament. Hyperflexion fractures are commonly associated with acute disc herniations. The flexion teardrop fracture results from most severe flexion forces. The posterior and anterior ligaments and the disc are disrupted. An anterior inferior corner fracture of the vertebral body–“teardrop” is present. Severe cord injury is mostly present (Fig. 6). When a significant rotational component with hyperflexion is present, unilateral (bilateral) facet dislocation may occur. The body of the dislocated vertebra is anteri-

Fig. 9a, b A frontal car collision (“hangman’s fracture”). a Anterior–flexion forces on the head and b following hyperextension forces resulting in spinal and facial fractures

orly displaced less than 50% of the width of the subjacent vertebra. Widening of the interspinous process is present. The articulating facets are no longer in opposition and have been described as “uncovered” (Figs. 7, 8). This injury represents the typical fracture dislocation, which shows in 75% of cases a neurological deficit. Hyperextension fractures Extension injury of the cervical and thoracolumbar spine results in the backward rotation or translation of the vertebra in the sagittal plane. It often results from an anterior impact on the mandible, face, or forehead, or from sudden deceleration. They are less frequent than flexion fractures. Facial injury often gives a clue to the hyperextension mechanism and is usually accompanied by cen-

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Fig. 10 a Lateral dislocation of the atlas representing a Jefferson fracture. b Axial CT of C1: burst fracture. c Axial CT of L3: burst fracture with narrowing of spinal canal

differentiated three different types depending on the location of the fracture [9]. Most commonly this fracture is found in frontal car accidents where the driver and/or cofrontal passenger are not using seat belts. When disc rupture and extension into the anterior and posterior longitudinal ligaments occur, anterior subluxation of C2 on C3 indicates instability (Fig. 9). Hyperextension injuries assume great importance in patients with pre-existing spinal problems including ankylosing spondylitis and congenital or acquired cervical stenosis. Vertical compression fractures

tral cord syndrome (oedema) and diffuse prevertebral soft tissue swelling. Pathologically, rupture of the anterior longitudinal ligament is accompanied by disruption of the intervertebral disc. Avulsion fracture of the anterior arch of the atlas and extension teardrop fracture are limited to the anterior column of the cervical spine, whereas isolated fracture of the posterior arch of the atlas and laminar fractures are limited to the posterior column. They are considered relatively stable. In more severe hyperextension injuries, however, at least two columns are disrupted, with resultant instability. Such fractures include hangman’s fracture (better: hanged man fracture). Hangman’s fracture is a C2 fracture involving the pars interarticularis and adjacent structures. Effendi et al.

Axial loading injury of the cervical and thoracolumbar spine results from forces transmitted through the skull and occipital condyles to a voluntarily straightened spine. Typical representatives are the Jefferson fracture of the atlas and the bursting fracture in the lower cervical and thoracolumbar spine (Figs. 10, 11). Burst fractures are either stable or unstable. The encroachment of the spinal canal may lead to cord injuries in up to 50% of cases. The Jefferson’s fracture consists of simultaneous disruption of the anterior and posterior arches of C1 with or without disruption of the transverse atlantal ligament. Identification of transverse disruption, with resultant atlanto-axial instability, is crucial in the thorough evaluation of this injury. Separation of the lateral masses from the dens of >7 mm implies instability due to tearing of

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Fig. 12 Three types of odontoid fractures: avulsion fracture of the tip of the odontoid process (left); fracture through the base of the odontoid process (right); fracture through the body of C2 evaluation with facet joint involvement (bottom)

Fig. 11 Radiograph of cervical spine (lateral): anterior compression fracture of C7. Straightening of the cervical spine

Fig. 13 Computed tomography of C1 and C2, lateral reconstruction: odontoid fracture type III

transverse ligament. Magnetic resonance imaging is highly suitable for the display of these abnormalities.

understood. Hyperflexion is believed to play a major role. Anderson and D’Alonzo [1] defined a classification based on the location of the fracture (Figs. 12, 13): type 1 is an avulsion fracture of the tip of the dens; type II, the most common odontoid fracture, represents a transverse fracture of the dens above the body of C2. Displacement of fragments is frequent and a high incidence of nonunion results from compromise of the blood supply. Finally, type III shows a fracture of the superior body and superior articulating facets.

Atlanto-axial fractures Atlanto-axial dissociations may be caused by distraction with superior displacement of the atlas and skull, or by odontoid fractures with resultant anterior and posterior displacement of the atlas; the former is primarily the result of ligamentous disruption. Dislocations may occur in an AP dimension or as rotary subluxation. These injuries may occur with tearing or laxity of the transverse ligament. The atlanto-dens distance is abnormally increased (>3 mm in adults). Odontoid fractures, however, are the most frequent cause of bone injury in the atlanto-axial region. The mechanisms of injury in odontoid fractures are not well

Long-term posttraumatic changes in the spinal cord In severe spinal trauma with cord damages follow-up of patients over a period of 20 years revealed the development of atrophy in 62%, myelomalacia in 54%, syrinx in 22%, cysts in 9% and disruption in 7%. The image mo-

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Fig. 14 a Magnetic resonance imaging of cervico-thoracal spine (lateral, T1-weighted), 15 years after ski accident: elongated hypointensity within cord. b T2-weighted (same patient as a: elongated hyperintensity within cord representing a syrinx)

dality of choice in the follow-up of these patients is MRI (Fig. 14).

Optimal work-up of patients with severe spinal trauma Multi-slice spiral CT with reconstructions rules out or proves any bony abnormalities (e.g. fractures, dislocation) with highest precision. Conventional radiographs are diagnostically insufficient and, in the cervical spine in up to 57% of cases, false negative. The CT protocol of the spine must include neighbouring anatomical structures (e.g. aorta, vena cava, bladder). According to the injury mechanism anteriorly lying soft tissue structures, such as the heart or bony elements (e.g. sternum, ribs), must be inspected also. A different work-up could be started if the spinal trauma did occur more than 6–10 h previously. In this case MRI with short tau inversion recovery sequences or T2-weighted sequences might be the most sensitive and first imaging modality showing, for example, haematomas, bone marrow oedema, cord injuries, ligament ruptures and disk herniations with highest precision (Fig. 15), whereas spiral CT would be used only in those anatomical regions where MRI shows an abnormality. This could be of great importance in cases of multi-level lesion. The disadvantage is the complicated management of these patients with, for example, life-saving lines, tubes and cables.

Fig. 15 Magnetic resonance imaging of thoraco-lumbar spine (lateral, T2-weighted): hyperintensity within the body of L3 representing the well-known burst fracture with neurological deficits. Additionally, there are multiple bone marrow oedema at Th5–Th8 with compression of the cord. (Metallic artefacts at L2 and L4)

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