Unicameral Bone Cyst

  • Etiology:
  • Imaging:
    — Location (metaphysis, intramedullary)
    — Lytic with thin sclerotic margin, usually unilocular, dependent bony fragment is evidence of fracture (fallen fragment sign)
    — Matrix ()
    — Zone of transition (narrow)
    — Periosteal new bone or cortical destruction (none)
  • DDX:
  • Complications:
  • Treatment:
  • Clinical:

Cases of Unicameral Bone Cyst

Radiograph of unicameral bone cyst of the ulna
AP (left) and lateral (right) radiographs of the forearm show a diaphyseal lesion that is expansile and lytic in appearance with a narrow zone of transition and no periosteal reaction.
Radiograph and CT and MRI of unicameral bone cyst of the femur
AP radiograph of the hip (upper left) shows a metaphyseal lesion that is expansile and lytic in appearance with a narrow zone of transition and no periosteal reaction. There is a transversely oriented linear density within it representing a fallen fragment sign. Coronal CT without contrast of the hip (upper right) better shows the cystic nature of the lesion and the fallen fragment. Coronal (left lower) T2 MRI without contrast of the hip shows the cystic nature of the lesion and axial T2 MRI (right lower) shows fluid / fluid levels within the lesion due to hemorrhage.