Extraosseous Signal Changes on Magnetic Resonance Imaging in Pediatric Patients with Early-Stage Lumbar Spondylolysis

Purpose : To analyze extraosseous signal changes (ESCs) on magnetic resonance imaging (MRI) in pediatric patients with stress fractures occurring in the lamina. Methods : This study was a retrospective review of 69 consecutive pediatric patients with stress fractures occurring in the lamina. We analyzed MRI scans obtained at the first presentation. Results : We used mainly axial short tau inversion recovery images acquired through the pedicle of these 84 fracture sites to identify the ESCs. These were then divided into three groups: “invisible” when no ESC was detected, “periosteal” for ESC seen on only the dorsal side of the lamina, and “perimuscular” for ESC distinctly spread around / in the paravertebral muscles. In total, 78 (92.9%) fracture sites showed ESCs on the dorsal side of the lamina among which 72 ESCs were located on only the “dorsal” side, while 6 ESCs were on the ventral side against the transverse process. Conclusion : ESCs on MRI were detected in more than 90% of patients before stress fracture became apparent in the lamina, which was considered similar to findings of periosteal thickening / edema detected at the onset of stress fracture in long bone.