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Marrow STIR Signal Underestimates Odontoid Fracture Acuity in Older Patients 2013

Category General Spine Forrester Lensing
Lubdha Shah, MD
Richard Wiggins
Purpose STIR hyperintensity is routinely used to assess for marrow edema to indicate an acute fracture. However, STIR may not accurately depict the acuity of a C2 fracture in older osteoporotic subjects. This may be explained by the intrinsic structural heterogeneity of the dens with reduced trabecular bone volume and decreased cortical thickness as well as histologic changes that occur with osteoporosis. The overall decreased bone mass reduction of the dens in osteoporotic patients with residual fat in the intertrabecular space may display diminished edema on STIR images with acute injury. This is clinically relevant as there is high fracture nonunion, especially in older osteoporotic patients, when treated with external immobilization if there is delayed treatment. Furthermore, several series favor surgical fixation of C2 fractures in older patients, reporting better results when performed in the acute stage (< 6 months). Materials & Methods The RIS was queried for “C2 fracture,” “dens fracture” and “odontoid fracture” from 2007 to 2012. Those cases with both CT and MRI were included. Patient demographics were recorded. The odontoid fractures were categorized into the 3 types as initially described by Anderson and D’Alonzo. The images were evaluated for the presence of STIR hyperintensity in the bone marrow and fracture cleft. The angulation of the fracture fragments was also evaluated. Results In the study population meeting inclusion criteria, there were 24 females and 22 males with an average age 62.5 years. The odontoid fracture type distribution was 33 type 2, 12 type 3 and 1 type 1. Though 50% of patients < 60 YO, demonstrated STIR hyperintense marrow signal, only 38% of patients < 60 YO had similar findings. A trend towards a negative correlation between age and STIR was seen in our group of patients. The average age of patients with a paucity of STIR signal (68.7 years +/- SD 21.6) was greater than that with STIR abnormality (54.4 years +/- 26.1). This age difference was found to be statistically significant (p<0.5). Conclusion It is important to be aware of this STIR MR pitfall when assessing the acuity dens fractures. Patients older than 60 years, particularly with osteoporosis, may have acute odontoid injuries without correlative hyperintensity on STIR imaging. Further weight should be placed on multidetector CT findings and clinical history in this setting. References
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