School ager with lower back and left buttock pain and a limp

Radiograph and MRI of aneursymal bone cyst
Lateral radiograph of the lumbar spine shows an expansile lesion in the S2 vertebral body. Axial and sagittal T2 MRI of the lumbar spine shows the S2 expansile lesion to be well defined and to have fluid-fluid levels within it.

The diagnosis was aneurysmal bone cyst of the sacrum.