Long-term follow-up of a case of aneurysmal bone cyst in the lumbar spine.

Background Context: Aneurysmal bone cyst (ABC) in the spine is relatively rare, so little is known about the natural history of the disease.

Purpose: The purpose of this study was to describe a spinal ABC that was followed for an extended period from lesion enlargement to spontaneous regression.

Study Design: Case report.

Methods: A 63-year-old woman had a 1-year-long history of mild low back and bilateral leg pain without any significant neurologic deficits caused by lumbar spinal stenosis. At her first visit to our hospital, magnetic resonance imaging (MRI) showed a small cystic lesion on the left side of the L5 vertebral body. The patient's clinical symptom progression and MRI and computed tomography evaluations were reported for >13 years.

Results: After 6 years, the cystic lesion enlarged significantly and extended into the left pedicle and transverse process of the L5 vertebra. The lesion was diagnosed as an ABC based on multilocular cysts with fluid-fluid levels on MRI and bony septations on computed tomography. Thirteen years after the first visit, the lesion regressed spontaneously without a clear reason, such as biopsy or fracture, and most of the lesion was replaced by fatty marrow. The patient's symptoms stabilized without neurologic deterioration during the follow-up period.

Conclusions: Although spinal ABC is an expandable cystic lesion, we should consider that such a lesion in an elderly patient could spontaneously regress.