The Presence or Absence of Marrow Edema - Essay Example

? Marrow Edema Variability in Acute Spine Fractures Mark A. Brinckman, M.D. Cam Chau, M.D Jeffrey S. Ross, M.D. Barrow Neurological Institute St. Joseph Hospital and Medical Center Department of Neuroradiology 350 W Thomas Rd Phoenix, AZ 85013 Abstract Background and Purpose: The presence or absence of marrow edema relate to the assessment of fracture acuity in MR imaging. Significant, there is variability in the degree of bone marrow edema in the acute trauma setting, particularly in hyperextension and/or distraction mechanisms of injury. Our aim was to characterize the utility of marrow edema in the determination of fracture detection and fracture acuity on MRI. Materials and Methods: We conducted a retrospective review of 1215 patients at our hospital for the acute work-up of spine trauma that underwent a combination of CT and MRI. We assessed the patients for the presence or absence of fracture, location, and type of fracture, and absence or degree of marrow edema. Results: The investigation identified 189 patients who had acute fractures on initial screening CT subsequently imaged by MR. 85 out of 189 generated no marrow edema. The majority of these 85 cases were in patients whose history suggested either a hyperextension or a distraction mechanism of injury. Five out of the 85 originated from axial load injury and involved C1 Jefferson fractures. Conclusion: There is variability in the presence or degree of marrow edema resulting from traumatic injury. Only those fractures derived from hyperflexion reliably generate marrow edema. Fractures derived from hyperextension, distraction, and axial loading, do not generate marrow edema, and can lead to a false negative MRI. An awareness of fracture types and traumatic mechanisms that lead to marrow edema is significant in evaluating acute trauma patients. Introduction Multi-detector computed tomography (MDCT) has become the most accurate, efficient, and cost-effective means of identifying fractures of the spinal column in the acute trauma setting.1,2 Despite the obvious advantages of MDCT in this setting, Magnetic Resonance Imaging (MRI) often serves a necessary secondary role when the acuity of the fracture may be in doubt. MRI also apply when soft tissue or ligamentous injury is sought, when epidural or cord hematoma is in question, or when vascular injury is suspected.3-12 With the increasing availability of MRI in the trauma setting, many patients are being evaluated by both modalities during the course of their acute injury work-up. Because of this increased utilization, radiologists must become familiar with the benefits and inherent limitations of each modality in the acute trauma setting. (3, 13, 14) Previous investigations have reported a poor sensitivity and high false negative rate for MRI in the detection of acute osseous fractures. (3, 13) Specifically, an early study in the utility of MRI in acute spinal trauma suggested that fractures of the compression or burst variety were often easier to detect.26 With regard to MRI utilization for acute fracture detection and/or acuity evaluation, we have anecdotally noticed that certain fracture types or fracture mechanisms often result in very little or no marrow edema. While we can infer the acuity of injury from the clinical history or from associated imaging findings, the reliability of marrow edema as a finding for acute fracture varies. The aim of this study was to investigate the variability of marrow edema in the acute trauma setting and characterize which fracture types or mechanisms can relevantly generate, or not generate, bone marrow edema. Based our anecdotal experience, we hypothesized that hyperextension and/or distraction mechanism injuries are most likely to not generate marrow edema and may directly contribute to the high false negative MR examination in acute spinal osseous injury. Materials and Methods After institutional board review approval and with Health Insurance Portability and Accountability Act compliance, we evaluated patients using a combination of CT and MR for acute spine trauma over a two-year period (August 1, 2009 and July 31, 2011). We entered data stored it, and evaluated it in an Excel spreadsheet. We performed the CT imaging without intravenous contrast on a 64-slice GE Light speed multi-detector scanner using the following standard protocol: 0.625mm x 64 mm collimation with 0.625 mm-thick sections, a 0.625 mm overlap, and a pitch of 0.984. We subsequently reconstructed the axial images at 2.5 mm and 2 mm slice spacing for review and storage on a PACS workstation. We routinely obtained reformations in coronal and sagittal planes from 0.625 mm axial reconstructions. We further reformatted the Multi-planar reformations to 0.7 mm thickness every 2 mm through the spine. In addition, we generally used an 18 cm FOV, 120 kV, and 100-715 smart mAs. Nevertheless, we conveniently altered these factors to accommodate a patient's body habitus. We analyzed the images using a preset bone window with a window level of 2500-500 HU and a window width of 400-40 HU. MR imaging was performed with either 1.5T or 3T magnet. We also acquired Sagital T1, T2, and STIR images. In addition, we acquired the Axial T2 FSE and/or axial MERGE images. Subsequently, we utilized the STIR sequences to determine the presence or absence of marrow edema with parameters as follows: Cervical spine entailed TR 45 ms/TE 2925 - 4500 ms; TI 135 - 165; matrix size 320 X 192; FOV 24 mm; section thickness/spacing of 3.5/0.5 mm. Thoracic spine entailed TR 42 - 45 ms/TE 3025 - 4075 ms; TI 135 - 170; matrix size 320 X 192; FOV 32 mm; section thickness/spacing of 3.5/0.5 mm. Lumbar spine entailed TR 42 - 45 ms/TE 2800 - 4500 ms; TI 135 - 170; matrix size 320 X 192; FOV 30 mm; section thickness/spacing of 4.5/0.5 mm. Two radiologists (MB and CC) retrospectively reviewed 1215 patients between August 1, 2009 and July 31, 2011 evaluated for acute spine trauma by a combination of CT and MRI. All imaging took place during a single admission. Average age of the patient population evaluated was 48.59 (+/- 22.54) years old. We excluded cases from the initial set of 1215 patients if they did not have a least one fracture of the cervical, thoracic, or lumbar vertebral column. We equally excluded from consideration patients with fractures only involving the skull base, ribs, sacrum, and/or pelvis. From this initial set of 1215 patients, 199 patients had a fracture identified by CT which we subsequently evaluated by MRI (199/1215 or 16.38%). The average age of this subset was 52.87 (+/- 23.37) years old. From the set of 199 patients, seven patients were excluded from further evaluation that had compression fractures confirmed by history and/or by prior imaging to be remote or chronic fractures. Three additional cases were excluded for inadequate MR evaluation. The remaining 189 patients with acute fracture injuries had an average age of 52.84 (+/- 23.62) years old. Analysis of the 189 remaining cases was performed with categorization of each patient’s type of fracture(s) present based on commonly used radiological descriptors (e.g., Jefferson, Odontoid, Clay Shoveler’s, etc.) 15, type of presumed primary mechanism (flexion, extension, axial load, mixed, or indeterminate) 15-24, and degree of marrow edema25. Two radiologists agreed upon primary spinal mechanisms independently (MB and CC) based on the pattern of osseous, soft tissue injury observed on CT, and MRI supplemented with clinical history where available in accordance with conventional patterns of injury for particular fracture types15-24. We qualitatively assessed the degree of marrow edema and then placed it into one of four quantifiable categories termed a Marrow Edema Score (table 1). The Marrow Edema Score (MES) assigned those cases with no identifiable marrow edema or edema confined to the fracture line, a score of one. Those cases with fracture line edema plus mild adjacent marrow edema (less than 25% of the vertebral body) recorded a score of two. Those cases with moderate marrow edema (easily identifiable marrow edema involving greater than 25% and less than 75% of the vertebral body) attained a score of three. Lastly, those with severe edema (greater than 75% of the involved vertebral body) achieved a score of four (table 1). If multiple fractures were present, an overall mean score applied to facilitate comparison among primary injury mechanisms and patterns. Statistical analysis was preformed utilizing one-way ANOVA with Tukey-Kramer Multiple Comparison Test using GraphPad InStat version 3.10 for Windows 7, GraphPad Software, and San Diego California USA. Two by two contingency testing was performed utilizing Fischer’s Exact Test also utilizing GraphPad InStat version 3.10. Results A two-year retrospective inquiry of 1215 patients evaluated for suspected acute spinal trauma identified 189 patients with 418 acute fractures of the cervical, thoracic, and lumbar spine. From the 418 identified fractures, we satisfactorily evaluated 369 fractures by a combination of CT and MRI. The degree of marrow edema (based on the Marrow Edema Score or MES) associated with these 369 fractures resulted in a set of 166 fractures demonstrating no marrow edema (MES=1), 64 fractures associated with mild marrow edema (MES=2), 54 fractures with moderate marrow edema (MES=3), and 85 fractures with severe marrow edema (MES=4). We organized the fractures according to vertebral body level, number of fractures at each vertebral body level, and mean marrow edema scores for each respective level (Table 2 and Figure 1). From the 189 patients evaluated in detail, there were 85 patients (85/189 or 44.97%) with 137 fractures demonstrating no marrow edema or fracture line edema only (MES of 1). In addition, we did not evaluate the additional 36 fractures (from173 fractures) in this subset using the both CT and MR. The remaining 104 patients (104/189 or 55.03%) sustained injuries that resulted in 232 fractures and had average marrow edema scores greater than one. Some of the fractures within the overall acute injury pattern resulted in no marrow edema (29/232 or 12.5%); however, the clear majority of fractures (203/232 or 87.5%) and overall pattern of injury resulted in marrow edema being present at one or more levels. Specifically, there were 64 fractures with mild marrow edema (MES=2), 54 fractures with moderate marrow edema (MES=3), and 85 fractures with severe marrow edema (MES=4) in this subset. Thirteen additional fractures (for an overall 245) were present in this group, but we did not evaluate them adequately by both CT and MR. A comparison of these two patient groups (85 and 104) against the set of 1026 patients with CT/MR evaluations that did not result in detection of a fracture approximates overall sensitivity, specificity, and predictive values for this retrospective analysis(table 3). In this light, marrow edema as a finding or indicator of acute fracture demonstrates a low overall sensitivity of 55%. This finding is consistent with a prior prospective investigation, which indicated a sensitivity of 55%3. Conversely, the poor sensitivity results in a high false negative rate of 45% for the finding of marrow edema by MRI in our evaluated population. In order to further investigate and understand which fractures types, levels, and/or mechanisms reliably generate marrow edema, we carried out an additional characterization and statistical analysis. For this analysis, we considered fracture mechanisms consisting of extension, axial load, flexion, mixed, and indeterminate for each acute injury case. Assuredly, we also assigned a mean marrow edema score based on the overall injury pattern. We also noted additional characterization as to level and commonly used fractures names when applicable. The number of patients with no appreciable marrow edema (MES=1) totaled 85 and accounted for 137 fractures evaluated by CT and MRI. Average age of this group was 52.48 years old +/- 24.38. There were 57 cases (57/85 or 67.06%) in this group, which appeared to represent primarily extension mechanism injuries. Within this subgroup, we also noted two sizeable fracture types. There were 27 cases with odontoid process fractures and 14 cases with a notable distraction component. The extension-distraction cases were composed primarily of extension injury in the setting of ankylosis and/or extension injury involving fractures through the disk/adjacent endplate. There were five cases (5/85 or 5.88%) in this group, which were of the axial load variety. All five cases were Jefferson fractures of the C1 Vertebral level. There were five cases (5/85 or 5.88%) in this group considered the result of a mixed pattern of mechanisms. Among these, three cases appeared to combine extension (odontoid process) and axial load (Jefferson), one case combined flexion and extension, and one case combined flexion-distraction (clay Shoveler’s) with extension (disk/end plate fracture). Among the remaining 23 flexion mechanism cases (23/85 or 27.01%), two subcategories were identified. A set of seven cases appeared to combine flexion with a notable distraction component. Within this set of seven cases, flexion-distraction with subluxation and clay Shoveler’s fractures were the two most common patterns. The larger set of 16 cases was composed of an assortment of limited flexion injury that was typically isolated to the pedicolaminar region, spinous processes, articular pillars, or anterior endplates. Mechanistically, we can characterize these 16 cases as flexion injury fractures combined with a rotational or lateral component. In contradistinction to the group of 85 cases with no marrow edema (MES=1), 66 cases were identified with moderate to severe marrow edema (MES=3 to 4). This group represents a mean marrow edema of 3.56 overall +/- 0.46. Average age within this set was 51.73 years old +/- 23.02. This group was homogenous with the vast majority of these cases (64/66 or 96.97%) composed of flexion mechanism injuries. Most, if not all, of these 64 cases characterize as vertebral body compression injuries with varying degrees of height loss or trabecular microfracture. Of the two cases in the minority, one case in this set represented a mixture of flexion (compression at T3) with extension (odontoid process fracture). We equally considered the other case as an indeterminate mechanism case, likely the result of traumatic bullet injury. The remaining 38 cases bridge the gap between the two aforementioned groups with mean MES greater than one and less than three. The 38 cases in this category had an overall mean MES of 2.03 +/- 0.35 (range of 1.25 to 2.67). Average age within this group was 55.55 years old +/- 23.36. This group represents a blend of the two previously described categories. The higher MES end of this inhomogeneous group is largely composed of flexion or vertebral body compression injury. The lower MES end contains a notable number of extension or odontoid process fractures. Between these two polar ends, we saw a limited amount of crossover. The majority mechanism within this group was the flexion category consisting of 25 cases (25/38 or 65.79%). The mean MES in this subcategory was 2.04 +/- 0.42. Two of the flexion cases contained a notable distraction component, both with mean MES of 2. There were eight cases of extension mechanism injury in this group (8/38 or 21.05%) with a mean MES of 1.94 +/- 0.18. Seven of these contained an odontoid process fracture and two of the eight had features suggesting a distraction component in addition to extension. The remaining six cases were composed of five mixed mechanism injuries and one indeterminate case. Four of the five mixed cases contained an odontoid fracture with a mean MES of 1.25 if considered in isolation. The combination of odontoid process fractures with flexion injury accounts for the higher overall score. There were statistically significant differences in the marrow edema scores of the flexion injury group when individually compared to the other three mechanisms of extension, axial load, and mixed (p Read More