Progression of a lumbar spinal osteoblastoma.

A 24-year-old woman presented with a lumbar spinal osteoblastoma manifesting as a 5-year history of low back pain radiating to the left foot. Neuroimaging showed suspicious hypertrophy of the left L4-5 facet which transformed in 3 years to an expansile mass lesion that compressed the dura mater and neural structures. Primary benign bone tumors such as osteoblastoma and osteoid osteoma should be considered in the differential diagnosis of back pain and the patients should be followed up carefully.