Differential Diagnosis
- Single most likely diagnosis
- Bilateral spondylolysis of L5 with nonunion or fibrous union: This diagnosis is most likely due to the presence of L5 spondylolyses distracted by 1 mm on the right and 3 mm on the left, with no evidence of bridging bone on either side, as seen on the CT scan. The MRI also showed abnormal marrow edema in the left pedicle and pars interarticularis of L5, suggesting a stress reaction or stress injury.
- Other Likely diagnoses
- Grade 1 anterolisthesis of L5 on S1: This diagnosis is likely due to the presence of grade 1 anterolisthesis at L5-S1 with mild narrowing of the left neural foramen, as seen on the CT scan.
- Interosseous hemangioma: This diagnosis is likely due to the presence of a 2 cm lesion in the right side of the sacrum at the S1 level, demonstrating mixed signal intensity on the T1-weighted images and increased signal on the T2-weighted images, as seen on the MRI.
- Mild disc bulging at L4-5 and L5-S1: This diagnosis is likely due to the presence of mild central and lateral bulging discs at the L4-5 and L5-S1 levels, as seen on the MRI.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Spinal cord compression or cauda equina syndrome: Although the CT scan did not show significant encroachment on the thecal sac or neural foramina, it is essential to consider these diagnoses due to the potential for severe consequences if missed.
- Osteomyelitis or discitis: Although there is no evidence of infection on the CT scan or MRI, it is crucial to consider these diagnoses due to the potential for severe consequences if missed.
- Rare diagnoses
- Osteoid osteoma: This diagnosis is rare, but it could be considered due to the presence of a lesion in the sacrum, although the MRI characteristics are not typical for osteoid osteoma.
- Aneurysmal bone cyst: This diagnosis is rare, but it could be considered due to the presence of a lesion in the sacrum, although the MRI characteristics are not typical for aneurysmal bone cyst.