Access Keys:
Skip to content (Access Key - 0)

Unicameral bone cyst

Tumor biology

  • Benign cystic lesion of bone.
  • Lesion is filled with yellow-green fluid (may be blood-tinged if pathologic fracture has occurred)

Age

  • 80-90% of patients are younger than 20 years of age
  • Younger patients tend to have more active lesions

Gender

Slight male preponderance

Presentation

  • Lesions may be asymptomatic and identified incidentally
  • 50% of patients present with pathologic fracture, often due to minimal trauma
  • Some patients present with swelling or stiffness of adjacent joint

Physical findings

Tender if fractured; fractures often incomplete or stable

Blood work

Aspiration of cyst yields fluid high in alkaline phosphatase

Plain films

Conventional radiographs usually diagnostic; other radiographic tests not generally required

Site
  • Central medullary lesion
  • Thought to begin in metaphysis and migrate into diaphysis with bone growth
    • Lesions are metaphyseal or metaphyseal/diaphyseal; can transverse physis and extend into epiphysis (very rare)
  • 80% of cases involve of proximal humerus or proximal femur
  • Other sites of involvement include ilium, calcaneus, and talus; usually found in older patients
Size

Lesions can grow to be quite large

Tumor effect on bone
  • Lytic lesions; borders somewhat lobulated
  • If patient has pathologic fracture, look for "fallen fragment" or "fallen leaf" sign; caused by cortical fracture fragment displaced centrally into fluid-filled cyst
Bone response to tumor
  • May have thin sclerotic margin
  • May cause bony expansion
  • Generally geographic lesions
  • May be new periosteal reaction in response to pathologic fracture, even if undisplaced
Matrix

None

Cortex
  • Not unusual for cortex to undergo endosteal erosion circumferentially
  • Periosteum usually not involved; however, will thicken following pathologic fracture
Soft tissue mass

None

Bone scan

Can demonstrate central cold area (fluid) with peripheral uptake

MRI: Unicameral bone cyst versus aneurysmal bone cyst

Aneurysmal bone cyst

  • Often multicystic
  • Fluid/fluid level in a cystic lesion generally aneurysmal bone cyst
  • Markedly expansile.

Unicameral bone cyst

  • Will have a fluid/ fluid level only if hemorrhage has occurred secondary to fracture
  • Only minimal bony expansion

Differential diagnosis

Based on expansile metaphyseal lesion in a child

  • Aneurysmal bone cyst
  • Generally eccentric with cortical erosion and neo-corticalization
  • Fibrous dysplasia
  • Chondromyxoid fibroma
  • Telangiectatic osteosarcoma
  • Infection
  • Nonossifying fibroma

Pathology

  • Gross: Cyst that may be fluid filled
  • Microscopic: If cyst wall obtained, will see fibrous tissue that may be lined by flattened spindle cells
  • Reactive bony changes may be present

Diagnosis and treatment

  • Plain films and aspiration usually diagnostic
  • Aspiration generally returns green-yellow fluid
  • If no fluid is obtained, or it is hemorrhagic, move to open biopsy
  • Repeated aspirations and injections of steroid or autologous bone marrow are treatments of choice in lesion without pathologic fracture
    • Technique may take 6-12 months to yield partially healed lesion
  • Pathologic fractures heal without undue delay and are unaffected by steroid injection
    • Generally one will delay treatment of a fracture until it is healed to prevent leakage of steroid
  • Curettage with bone graft may be indicated if structural integrity of bone is at risk
  • Local recurrence rate is high and increases with incomplete excision, however

Complications

Pathologic fracture

Peer Review

OrthopaedicsOne Peer Review Workflow is an innovative platform that allows the process of peer review to occur right within an OrthopaedicsOne article in an open, transparent and flexible manner. Learn more

Instructions for Authors

Read our Instructions for Authors to learn about contributing or editing articles on OrthopaedicsOne.

Content Partner

Learn about becoming an OrthopaedicsOne Content Partner.

Academic Resources

Resources on Unicameral bone cyst from Pubget.

The license could not be verified: License Certificate has expired!
Orthopaedic Web Links

Internet resources validated by OrthopaedicWebLinks.com

The license could not be verified: License Certificate has expired!
Related Content

Resources on Unicameral bone cyst and related topics in OrthopaedicsOne spaces.

Page: Unicameral bone cyst (OrthopaedicsOne Articles)
Page: Osteoid osteoma (OrthopaedicsOne Articles)
Page: Chondroblastoma (OrthopaedicsOne Articles)
Page: Fibrous dysplasia (OrthopaedicsOne Articles)
Page: Giant cell tumor (OrthopaedicsOne Articles)
Page: Osteoblastoma (OrthopaedicsOne Articles)
Page: Aneurysmal bone cyst (OrthopaedicsOne Articles)
Page: Eosinophilic granuloma (OrthopaedicsOne Articles)
Page: Osteochondroma (OrthopaedicsOne Articles)
Page: Fibrous cortical defect (OrthopaedicsOne Articles)
Showing first 10 of 449 results