Bone SPECT/CT and MRI in pediatric patients with low back pain and suspected spondylolysis

Objectives To compare bone SPECT/CT and MRI findings in pediatric and adolescent patients with low back pain and suspected spondylolysis of the mid or lower lumbar spine.

Methods 67 school age and adolescent patients had bone SPECT with very low dose CT and MRI for low back pain. Bone SPECT/CT and MRI were reviewed with special reference to pars interarticularis (pars) defects (on MRI and CT), abnormal Tc-99m-MDP uptake (on SPECT), and MRI findings. All choices of imaging modality were made by the referring physicians.

Results 16 patients had lumbar pars defects on CT. 10 of 16 had abnormal clefts in the same location on MRI (5 with localized edema). Five had no clefts on MRI, but had localized edema on MRI at the site of the spondylolysis on CT, and one had abnormal orientation of the pars on MRI. 12 of the 16 patients had increased MDP uptake on SPECT at the site of the spondylolysis. Of 4 patients with spondylolysis and no abnormal uptake on SPECT, 3 had spondylolisthesis with normal SPECT and no edema on MRI. Two patients had increased pedicle uptake without spondylolysis, one had normal CT and MRI findings and the other had both sclerosis on CT and edema on MRI. Intervertebral disk abnormalities were noted in 8 patients, 5 were positive only on MRI, 2 on both CT and MRI and only one on CT. Abnormal sacroiliac joint uptake was noted in 2 patients, only one had abnormalities on CT and MRI.

Conclusions In patients with lumbar spine spondylolysis by CT, a high percentage will have increased uptake on SPECT. MRI will demonstrate a visible cleft in approximately 2/3 of cases. In other patients with spondylolysis on CT, the most common MRI finding is edema in the pars. . This localized edema is not specific for spondylolysis and is usually associated with increased uptake on bone SPECT/CT imaging, representing attempted bone repair of a stress injury or fracture