Review Question - QID 712

The pathologic fracture shown in Figure A is most likely through a unicameral bone cyst (UBC), and initial treatment should be conservative for fracture healing. UBCs occur most commonly in the proximal humerus and are characterized by cystic, symmetric expansion with thinning of the cortex. Although uncommon, the “fallen leaf” sign is seen when a piece of bone fractures off and is captured within the basin of the cyst floor and is characteristic of pathologic fractures thru UBCs. The proximal femur is the second most common site after the proximal humerus. Patients generally present with pain, usually after fracture resulting from minor trauma. Treatment of UBC begins with fracture healing, and if there is any question about diagnosis, advanced imaging and biopsy.

Some lesions decease in size or heal by skeletal maturity without treatment. For recalcitrant UBCs that continue to be symptomatic or are in high-stress locations then either a steroid injection or curettage with bone grafting has been recommended.

Margau et al reviewed MRI characteristics of of previously fractured UBCs and found they can appear complicated, with heterogeneous fluid signals and regions of nodular and thick peripheral enhancement related to early healing.