Diagnostic Radiology/Musculoskeletal Imaging/Tumors Basic/Aneurysmal Bone Cyst

An aneurysmal bone cyst is an expansile osteolytic bony lesion composed of blood-filled spaces separated by connective tissue septa of bony trabeculae or osteoid tissue and osteoclast giant cells

Epidemiology/Prevalence

 * Almost always present in patients < 30 years old. 80% in 5-20 year olds.
 * Very slight male to female predominance before 14 year old; after, slight female to male predominance (i.e. 1.16:1.00).
 * ~1% of all bone tumors.
 * 1.4 cases per 100,000 worldwide.

Types

 * 1) Primary (~70%) - no known cause or association with other bony lesion.
 * 2) Secondary (~30%) - occurs in conjunction with another lesion or trauma. Some suggest using ‘principal lesion concomitant with hemorrhagic or cystic changes’ instead. Typical primary lesions include eosinophilic granuloma, simple bone cyst, chondroblastoma, giant cell tumor, or osteosarcoma.

Clinical Presentation
Pain

Radiologic Findings

 * expansile
 * lucent lesion in the proximal tibial metaphysis and epiphysis
 * abutting the joint space
 * no periosteal reaction
 * no matrix evident
 * patient is skeletally immature (physeal plates not completely fused)

Location

 * ~60% in long bones (mostly metaphyseal and eccentric)
 * tibia, femur, and spine (posterior elements) top three locations
 * If in flat bones, majority in pelvis.

Differential Diagnosis

 * Osteoblastoma and osteoid osteoma (especially when location is posterior spinal elements)
 * Lytic metastasis (should have more aggressive features)
 * Unicameral bone cyst (usually central)
 * Giant cell tumor (skeletally mature, epiphyseal and abut articular surface when in non-flat bones)
 * Osteosarcoma (but typically has osteoid matrix, aggressive features)

Treatment
Biopsy is recommended to differentiate from more aggressive lesions. When primary, wide resection is recommended. If curettage alone is used, 25% recur. So when location makes wide resection unfeasible, aggressive curettage (i.e. liquid nitrogen, embolization, etc.) is needed. When secondary, treat the primary lesion.