Unicameral Bone Cyst
Simple Bone Cyst

Solitary Bone Cyst


 

General Considerations

  • Common (3-5% of primary bone tumors)
  • Benign
  • Solitary lesion
  • Most common in proximal humerus and femur
    • Also Iliac bone and calcaneous, especially over age 20
  • Most common between 4-10 years old
    • Males:Females 3:1
  • Filled with clear, yellowish fluid
    • May contain giant cells and hemosiderin 

Clinical Findings

  • Asymptomatic
  • If fractured, then
    • Pain
    • Limited range of motion 

Imaging Findings

  • Conventional radiography is the study of choice
  • Most common in proximal humerus (in patients under 20) and femur in skeletally immature male
  • Solitary, lytic metaphyseal lesion adjacent to, but not crossing, the epiphyseal plate
    • Migrates towards diaphysis during growth of child
  • Well-defined margins with narrow transition zone
  • May be slightly expansile
  • Long axis of lesion is parallel to long axis of bone
  • May have thin sclerotic margin
  • Endosteal scalloping and erosion
  • Fallen Fragment Sign represents a fragment of bone that falls into the cyst and then into a dependent position
    • Although uncommon, it is pathognomonic for a simple cyst because it indicates the fluid nature of the interior of this lytic lesion
  • On CT, they may be shown to contain air-fluid or fluid-fluid levels
  • On MRI. They will have low signal intensity on T1 and high on T2
    • Lesions which have fractured will have a heterogeneous signal on T1 and T2 because of the hemosiderin
    • Their periphery may enhance with Gadolinium
  • Photopenic on bone scan 

Differential Diagnosis

  • Fibrous dysplasia
    • Ground-glass; more irregularly shaped
  • Eosinophilic granuloma
    • Look for other lesions; beveled-edge; vertebra plana
  • Chondroblastoma
    • Extends into epiphysis
  • Chondromyxoid fibroma
    • More expansile and eccentric; more rare
  • Brown tumor
    • Other signs of hyperparathyroidism
  • Aneurysmal bone cyst
    • More expansile
  • Enchondroma
    • Smaller bones; internal calcifications 

Treatment

  • Curettage and bone grafting, nailing, injection of bone marrow or cryotherapy to prevent pathologic fracture
  • Methylprednisolone injections have been used to promote healing 

Complications

  • Pathologic fractures in 50-65%
  • Growth arrest in affected limb 

Prognosis

  • Usually undergo spontaneous regression

 

Unicameral Bone Cyst. A single frontal radiograph of the shoulder demonstrates a geographic lytic lesion (white arrow) in the metadiaphysis of the humerus with a sharp zone of transition. There is a pathologic fracture through the lesion (black arrows).
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Dahnert 4th Ed
Simple Bone Cyst eMedicine Eu-Leong Harvey Teo and Wilfred CG Peh