Aneurysmal Bone Cyst (ABC) of the Lumbar Spine
- Background:
- ABCs are benign expansile lesions of unknown etiology. They have blood–filled cystic spaces separated by fibrous septae, which consist of immature woven bone trabeculae, macrophages, giant cells, capillaries, and fibroblasts.
- Pathologic findings do not support the theory that these lesions represent a vascular degenerative process.
- Some samples may contain areas with tissue characteristics of a giant cell tumor, chondroblastoma, osteoblastoma, or fibrous dysplasia.
- Most aneurysmal bone cysts occur in the pediatric age.
- The spinal vertebrae are the second most frequent sites (around 15–30%) where the posterior elements are characteristically involved, although they can also extend to the vertebral body. The thoracic segment is the one most frequently affected.
- Relevant Clinical Information:
- Patients may be asymptomatic, but pain on palpation or pathologic bone fracture may be the first presenting signs.
- Key Diagnostic Features:
- Osteolytic, expansible lesion, with well defined sclerotic margins on computed tomography and x-rays.
- On MR examinations, fluid-fluid levels are a diagnostic feature, which represent hemorrhage in different stages of evolution.
- Septal enhancement after contrast administration is frequent.
- Imaging features without fluid-fluid levels by CT and MR may occasionally be nonspecific for diagnosis.
- Differential Diagnosis:
- Giant cell tumor: Older age group, a predilection for the vertebral body instead of the neural arch and a solid instead of a cystic behavior. GCT may be associated with ABCs.
- Osteoblastoma: May be associated with ABCs, but has a bone matrix best seen on CT or x-rays
- Metastasis: More frequent in older patients, tend to produce bone marrow replacement rather than expansile lesions and are more associated with cortical disruption and soft tissue masses
- Brown tumor: Elevated serum calcium levels may help to differentiate a brown tumor.
- Treatment:
- Surgical resection and bone chip packing or polymethylmethacrylate injection are the treatments of choice. Recurrence is more common in younger patients, with range of 5% to over 40%.
