Diagnosing aneurysmal and unicameral bone cysts with magnetic resonance imaging

The differential between aneurysmal bone cysts and unicameral bone cysts us ually is clear clinically and radiographically. Occasionally there are case s in which the diagnosis is not clear. Because natural history and treatmen t are different, the ability to distinguish between these two entities befo re surgery is important. The authors reviewed, in a blinded fashion, the pr eoperative magnetic resonance images to investigate criteria that could be used to differentiate between the two lesions. All patients had operative o r pathologic confirmation of an aneurysmal bone cyst or unicameral bone cys t. The authors analyzed the preoperative magnetic resonance images of 14 pa tients with diagnostically difficult bone cysts (eight children with unicam eral bone cysts and six children with aneurysmal bone cysts) and correlated these findings with diagnosis after biopsy or cyst aspiration and contrast injection. The presence of a double density fluid level within the lesion strongly indicated that the lesion was an aneurysmal bone cyst, rather than a unicameral bone cyst. Other criteria that suggested the lesion was an an eurysmal bone cyst were the presence of septations within the lesion and si gnal characteristics of low intensity on T1 images and high intensity on T2 images. The authors identified a way of helping to differentiate between a neurysmal bone cysts and unicameral bone cysts on magnetic resonance images . Double density fluid level, septation, and low signal on T1 images and hi gh signal on T2 images strongly suggest the bone cyst in question is an ane urysmal bone cyst, rather than a unicameral bone cyst. This may be helpful before surgery for the child who has a cystic lesion for which radiographic features do not allow a clear differentiation of unicameral bone cyst from aneurysmal bone cyst.