Spinal trauma in DISH and AS: is MRI essential following the detection of vertebral fractures on CT?

Background: Both ankylosing spondylitis (AS) and diffuse idiopathic skeletal hyperostosis (DISH) cause a rigid spine, but through different pathophysiology. Recent data has shown that characteristic fracture patterns may also differ following trauma since the posterior osseous and soft tissue elements are often spared in DISH. CT and MRI are important in diagnosing spine injury, but given the differences between AS and DISH, the utility of obtaining both studies in all patients warrants scrutiny.

Purpose: To assess the prevalence of posterior element injury on CT and MRI in DISH and AS patients with known vertebral body injury detected on CT; to determine whether MRI demonstrates additional injuries in neurologically intact patients presumed to have isolated vertebral body injuries on CT.

Study Design: Multicenter, retrospective, case-control study.

Patient Sample: DISH and AS patients presenting after spine trauma between 2007 and 2017.

Outcome Measures: Review of CT and MRI findings at the time of presentation.

Methods: One hundred sixty DISH and 85 AS patients presenting after spine trauma were identified from 2 affiliated academic hospitals serving as level 1 trauma and tertiary referral centers. A diagnosis of DISH or AS was verified by a board-certified emergency radiologist with 3 years of experience. Age, gender, mechanism of injury, fracture type, spine CT and MRI imaging findings, surgical intervention, and neurologic deficit were recorded. The CT and MRI studies were reviewed by the same radiologist for fracture location and type using the AO spine classification. No funding source or conflict of interest was present.

Results: Median age was 72 and 79 years old for the AS and DISH groups, respectively. Both were predominantly male (81%) and most presented after a low energy mechanism of injury (74% and 73%). Type C AO spine injuries were seen in 52% of AS patients but only 4% of DISH patients. In patients with known vertebral body injury on CT, additional injury to the posterior elements on CT or MRI in DISH patients was 51% versus 92% in AS patients. However, in patients with an isolated vertebral body fracture on CT and no neurological deficit, MRI identified posterior element injury in only 4/22 (18%) DISH patients compared to 5 of 7 (71%) AS patients. None of the MRI findings in the DISH patients were considered clinically important while all 5 AS patients eventually underwent operative treatment despite having no neurological deficit. Epidural hematoma on MRI was seen in 43% of AS patients as opposed to 5% of DISH patients.

Conclusion: Based on our small sample size, CT alone may be adequate in DISH patients with isolated vertebral body fractures and no neurologic deficit, but an additional MRI should be considered in the presence of an unclear neurological exam or deficit. MRI should be strongly considered for any AS patient regardless of neurologic status.