Successful treatment of a sacral aneurysmal bone cyst with zoledronic acid.

Background: Aneurysmal bone cysts (ABCs) in the sacrum pose a management challenge as their location usually means that surgical excision is not possible. Strategies such as embolization have been used previously but have the potential for significant side effects. We report the successful use of bisphosphonate treatment (zoledronic acid) in an 8-year-old boy who presented with an ABC that did not respond to embolization.
Methods: The patient presented with pain and progressive limp. After radiologic and histologic confirmation of the diagnosis, embolization therapy was trialed, which was unsuccessful. At this point, he had severe pain and extremely limited mobility, requiring the use of a wheelchair. His ability to lie flat or sit erect was limited by the pain. Zoledronic acid therapy was subsequently commenced at 0.04 mg/kg per dose by intravenous infusion, at 4 monthly intervals, for a total of 2 years (7 doses).
Results: The infusions were well tolerated, with rapid reduction in pain and resolution of previously severe immobility, from being bed and chair bound at baseline to normal independent ambulation over several months. This was associated with marked radiologic improvement. We postulate that the effect of treatment is a combination of the anti-inflammatory effect of zoledronic acid and the antiresorptive effect of osteoclast inhibition.
Conclusions: We conclude that bisphosphonates should be considered as possible second-line agents for ABCs. Further, study of a larger cohort would help to establish their efficacy in this setting.
Level of Evidence: Level IV (case report, no comparator/control arm).