Discussion
The main reason for adopting additional imaging after a negative CT scan result is to avoid potential catastrophic consequences of missed injury.12 On the other hand, obtaining MRI is costly, time-consuming, and carries potential risks to critically ill patients during transfer. Routinely adding MRI to all blunt trauma patients would represent a significant burden on the healthcare system and waste hospital resources. A recent study demonstrated that although the cost of MRI is substantial, over 5000 MRIs on obtunded patients would be required to match the cost of providing care for one quadriplegic patient, which far exceeded the number needed to be treated in their study.8 A review5 in 2012 indicated that since 2004, authors have conducted three meta-analyses7 ,15 ,19 on the subject, along with a review from the EAST.20 The latter EAST review concluded that due to the variability of screening performance, clinicians can clear the spine of obtunded trauma patients using MDCT alone or with MDCT followed by MRI with implications to either approach. As mentioned earlier, a recent EAST review, however, recommended cervical collar removal in the obtunded adult patient after a negative high-quality c-spine CT scan only.4 Some authors have suggested that additional testing should be evaluated on a patient-by-patient basis because MRI is more likely to detect certain types of injuries (eg, ligamentous instability) than a CT scan.10
A 7-year retrospective study—similar to ours—by Fisher et al8 advocated routine use of MRI in the evaluation of obtunded blunt trauma patients based on the observation that 5% of patients had clinically significant injuries with 3% requiring intervention. One major difference between that study and ours is the definition of ‘clinically significant’ injuries. In the Fisher et al study, change in management was assessed only after determination of clinical significance defined as the detection of specific MRI findings, regardless of their impact on management. In our study, we did not predefine injuries in order to establish ‘clinical significance’. MRI findings of patients that eventually underwent a change in management were deemed ‘clinically significant’ in retrospect, that is, only if they resulted in a change in management. A second difference between the two studies was the type of injuries encountered. In the Fisher et al study, a majority of patients had some form of ligamentous injury as opposed to disc lesions and cord contusions in our study.
One aspect that differentiates this study from others is that in addition to obtunded or unreliable patients, it incorporates the non-obtunded symptomatic or reliable patients in order to assess the value obtained from ordering the MRI on these patients. Additionally, it includes findings that may have been disregarded or often described as ‘degenerative’ or ‘non-acute’. This enables the evaluation of ‘acute on-top-of chronic’ events. Patients with chronic degenerative findings have higher vulnerability to injury following trauma, even minimal trauma. For example, patients with pre-existing disc bulges have higher vulnerability to post-traumatic disc prolapse. In addition, patients with degenerative central canal stenosis or foraminal narrowing have increased susceptibility of cord contusions or nerve compression. Finally, we note the susceptibility of osteophytes to fracture. In this study, the majority of patients with a positive MRI finding had a ‘disc lesion’. Among those, some had such finding as the only finding on the MRI and resulting in the collar being kept in place. Although these patients were all symptomatic and although the collar may have provided symptomatic relief, no evidence exists on the long-term outcomes of such practice.21 Physicians may often prescribe cervical collars by convection for patients presenting with neck pain.21 In our study, the MRI finding of disc lesions appears to have led to this practice.
Being a retrospective study, we could not directly assess the presence and severity of degenerative c-spine conditions prior to injury. Nonetheless, we were able to use the MRI findings to characterize these likely pre-existing abnormalities or those considered of a degenerative nature in relationship to the acute injury. For example, we could assess the presence and extent of osteophyte encroachment on the central canal causing narrowing. We hypothesize that the presence of such findings predisposes patients for a lower threshold to develop cord compression by having a diminished capacity to accommodate post-traumatic edema. This may render such patients more vulnerable for spinal cord compression following trauma. In this, and similar settings, the MRI was able to detect ‘acute on-top-of chronic’ events. Although the CT can detect degenerative findings, only the MRI can discern the presence, extent, and impact of injury to the spinal cord or root injury. In the acute setting, clinicians generally consider a CT scan that shows only degenerative disease as negative. A recent study has shown that the agreement of interpreting and reporting varying degenerative findings on cervical MRI has not been well assessed.22
Disc lesions were the only positive MRI finding in 45.3% of patients with positive MRI, of which only 6 patients (6/53, 11.3%) had a change in management. This raises the flag that in some patients with CT scans of the c-spine described as ‘negative’, detection of a disc lesion (usually considered ‘degenerative and non-acute’),23 may represent an acute on-top-of chronic cause that may explain post-traumatic symptoms; or represent traumatic exacerbation of existing disease that may require subsequent intervention. These findings are only more accurately assessed via MRI. Thus, a CT scan revealing chronic or degenerative changes does not necessarily exclude injury, and suspicion should be raised in blunt trauma patients with evidence of degenerative findings on the CT. MRI findings such as cord contusions, effacement of the ventral sac, or neural foraminal narrowing suggest that CT imaging alone lacks sufficient sensitivity to exclude injury. Significantly, falls in the elderly—a group of patients more likely to have chronic and degenerative c-spine conditions—represent a major proportion of admissions to emergency departments and trauma centers. We are not suggesting that every elderly patient who falls and has any sort of degenerative findings on CT should get an MRI; rather, we are trying to raise a flag that among elderly blunt trauma patients, the treating physician should maintain a high index of suspicion for injury even when they have a CT scan of the c-spine that is read as ‘negative for acute events'.
As with most studies, there were some limitations to this study. First, this is a single-institution, retrospective review. Since no protocol existed for ordering the MRI, we could not ascertain whether the presence of certain findings were the reason why the MRI was ordered. However, all patients who underwent MRI had neck pain or midline tenderness, neurological deficit, or were obtunded. We also relied on the CT and MRI reports interpreted by attending board certified radiologists, which may have carried the potential for subjective interpretation. Additionally, in retrospect, we could not ascertain the specific reasons behind the decision to change management, especially in the absence of predetermined treatment criteria or protocols. We cannot definitively conclude that the MRI findings alone led to the change in management, thus the possibility for individual spine surgeon's preference exists. Since we only included patients who had a negative CT scan followed by MRI (only 2.7% of our blunt trauma population), the potential for selection bias also exists. Because of this, it should be clear that the results of this study are to apply only to patients who are reliable yet at clinical suspicion for c-spine injury despite a negative CT scan or to those deemed unreliable for examination. Some data related to complications of prolonged cervical collar immobilization in patients with concomitant traumatic brain injuries (such as skin break down and elevated intracranial pressure even for short periods of time) were not available. Finally, estimation of radiologists' error rates or evaluation of CT films that may have been re-reviewed following the MRI results was not possible due to lack or incomplete documentation.
Even though the study/control groups were similar in age, gender, ISS, GCS, and type of blunt trauma, they had differences. Non-obtunded patients in the study group were at risk for a positive MRI because ‘clinical suspicion’ (presence of neck pain, neurological deficit, or possibly undocumented suspicion for injury or a false-negative CT) existed. This kind of ‘suspicion’ per se plays a role in determining whether the MRI should be ordered, and accordingly, represents a ‘risk’ for patients being predisposed for a positive MRI. It was almost impossible to include patients in the control group with the same ‘risk’ for a more accurate comparison because most of these type of patients would have most likely received the MRI and included in our study population. Our results demonstrate that among these groups of patients who were at this clinical suspicion or were unreliable for examination, the MRI was indeed of value as it represented a factor that contributed to alteration of patient management.
