Aneurysmal Bone Cyst




CLINICAL SUMMARY


Aneurysmal bone cysts (ABCs) derive their name from their radiologic appearance and therefore do not represent a single pathologic entity. Although many ABCs are actually secondary features of an underlying osseous neoplasm, there is a “primary” ABC, described herein, that probably represents a periosteal or cortical vascular malformation. In these cases, curettage is adequate.




DIAGNOSTIC FEATURES





















History


  • 80% between 5 and 20 years of age



  • Mild pain, slowly progressive



  • Occasionally, more rapid growth and even pathologic fracture

Location


  • The majority are metaphyseal and eccentric (80% to 90%)



  • Fewer are diaphyseal, cortical (10% to 20%)



  • Very large lesions can appear central in location

Margins


  • Geographic lysis



  • Cortical thinning and expansile remodeling



  • Cortex may not be visible on radiographs, suggesting aggressive behavior, but will be intact on CT or MRI

Matrix


  • No mineralized matrix






IMAGING





























  • ABCs appearing as eccentric metaphyseal lesions in the proximal tibia ( left ) and distal femur ( right ).



  • Note that the medullary margins are sclerotic but cortical borders appear more aggressive, due to marked thinning.



  • Neither lesion extends to subchondral bone, in contrast to giant cell tumor.










  • Diaphyseal lesion (10% to 20%) demonstrating cortical location in the humerus ( left ). Cortical margins in metaphyseal and diaphyseal lesions are similar.



  • Spinal lesion demonstrated by missing right pedicle, transverse process ( arrow ), and compression deformity of L4 ( right ).





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