Updated: 1/24/2018

Unicameral Bone Cyst

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Questions
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Evidence
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Videos
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Cases
4
https://upload.orthobullets.com/topic/8035/images/Case A - femur - xray - parsons_moved.png
https://upload.orthobullets.com/topic/8035/images/Case A - femur - T1- parsons_moved.png
https://upload.orthobullets.com/topic/8035/images/Histology A - Parsons_moved.jpg
https://upload.orthobullets.com/topic/8035/images/Case C - inactive - parsons_moved.png
https://upload.orthobullets.com/topic/8035/images/Case B - fallen fragment - parsons_moved.jpg
 
Introduction
  • Also referred to as a simple bone cyst
  • non-neoplastic, serous fluid-filled bone lesion thought to result from temporary failure of medullary bone formation near the physis
  • Age & location
    • age
      • usually found in patients <20 years of age
    • location
      • usually found in the proximal humerus of young patients 
      • can be found in other locations including proximal femur, distal tibia, ilium, calcaneus, and occasionally metacarpals, phalanges, or distal radius 
      • arises in the metaphysis adjacent to physis and progresses toward the diaphysis with bone growth
  • Prognosis
    • as a patient approaches skeletal maturity, a UBC will often decrease in size and may heal after growth is complete 
    • fracture healing usually does not lead to cyst resolution
    • requires close follow up while in active phase due to recurrence and risk of fracture or growth arrest 
Classification
  • Classification is important as it impacts treatment
    • active
      • if cyst is adjacent to the physis
    • latent
      • if normal bone separates cyst from physis 
Presentation
  • Symptoms
    • most asymptomatic unless fracture occurs (usually with minor trauma)
    • presents with pain from a pathologic fracture in ~50% 
Imaging
  • Radiographs
    • central, lytic, well-demarcated metaphyseal lesion (2-3% cross physis)
    • cystic expansion with symmetric thinning of cortices
    • "fallen leaf" sign (pathologic fracture with fallen cortical fragment in base of empty cyst is pathognomonic) 
    • trabeculated appearance after multiple fractures
  • MRI
    • very dark on T1 
    • very bright on T2 
    • gadolinium shows classic rim enhancement of a cystic lesion
  • Bone scan
    • is variable, but usually warm
Labs
  • Specific laboratory tests
    • usually not required 
Histology
  • Characteristic findings 
    • cyst with thin fibrous lining containing fibrous tissue, giant cells, and hemosiderin pigment 
    • chronic inflammatory cells may be found in small numbers
    • cementum spherules (calcified eosinophilic fibrinous material) in 10%
    • uniform population of spindle cells without nuclear atypia
  • Biopsy usually indicated for questionable diagnosis
Differential
  • ABC
    • is more expansive than UBC (UBC lesion usually not wider than physis)
  • Telangiectatic osteosarcoma
Treatment
  • Nonoperative
    • immobilization alone      
      • indications
        • proximal humerus lesions with pathologic fracture (15% of lesions fill in with native bone after acute fracture) 
    • aspiration/methylprednisolone acetate injection
      • indications
        • active cysts (communicates with physis) in the proximal humerus 
      • technique
        • usually requires several injections, especially in very young children
        • bone marrow injections have recently been reported to be effective 
  • Operative
    • curettage and bone grafting +/- internal fixation based on tumor location
      • indications
        • symptomatic latent cysts that have not responded to steroid injections
        • latent cysts in the proximal femur that are a structural concern and at risk for fracture and osteonecrosis
        • proximal femoral lesions with a pathologic fracture have a high rate of refracture and malunion when treated nonoperatively therefore, internal fixation is recommended 
      • contraindications
        • avoid in active lesions as communication with physis may lead to growth arrest
Differentials & Groups
 
"Bubbly" lytic lesion on xray
 
Treatment is USUALLY Aspiration and Injection
 Treatment is OCCASIONALLY curettage and bone grafting.  
UBC
 
 
ABC
       
NOF
     
Enchondroma        
 
 
Ibank
  Location
Xray
Xray
CT
B. Scan
MRI
MRI
Histo(1)
Case A femur
 
Case A humerus
 
 
 
 
Case A humerus
 
 
 
 
(1) - histology does not always correspond to clinical case

 

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Questions (20)
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(SBQ11PA.92) What is the most common anatomical site for unicameral bone cysts in children?

Review Topic

QID: 4117
1

Distal humerus

1%

(24/3541)

2

Proximal humerus

91%

(3223/3541)

3

Distal femur

4%

(131/3541)

4

Proximal tibia

3%

(98/3541)

5

Tibial shaft

1%

(49/3541)

ML 1

Select Answer to see Preferred Response

PREFERRED RESPONSE 2

(SBQ06BS.1) A 14-year-old boy is brought to the emergency department after falling onto his right shoulder. Radiographs are shown in Figure A. Which of the following is most likely complication to occur with curettage and bone grafting of this lesion? Review Topic

QID: 2513
FIGURES:
1

Metastases to the lungs

3%

(9/333)

2

Recurrence of the lesion

66%

(221/333)

3

Limb-length discrepancy of the affected side compared to the contralateral side

21%

(71/333)

4

Continued pain in the affected extremity

9%

(29/333)

5

Paraneoplastic disease

0%

(0/333)

ML 2

Select Answer to see Preferred Response

PREFERRED RESPONSE 2

(OBQ07.51) An 8-year-old boy injures his arm pulling open a car door. A radiograph is shown in Figure A. Which of the following is the most likely diagnosis and preferred initial treatment? Review Topic

QID: 712
FIGURES:
1

Giant cell tumor of bone, Open biopsy and curettage of tumor

2%

(28/1436)

2

Unicameral bone cyst, Aspiration of fluid and injection of bone cement

9%

(135/1436)

3

Non-Ossifying Fibroma, Radiation

1%

(12/1436)

4

Unicameral bone cyst, Sling and swath

88%

(1258/1436)

5

Telangietic osteosarcoma, Chemotherapy

0%

(1/1436)

ML 1

Select Answer to see Preferred Response

PREFERRED RESPONSE 4

(OBQ04.54) A 15-year-old boy twists his ankle and is brought to the emergency room. Radiographs are shown in Figure A. What is the most likely progression of the this lesion as the child reaches skeletal maturity? Review Topic

QID: 1384
FIGURES:
1

Increase in size and involve the entire bone

2%

(18/897)

2

Decrease in size and may disappear altogether

87%

(783/897)

3

Turn into a malignant tumor

0%

(2/897)

4

Remain unchanged

10%

(90/897)

5

Lead to deformity of the affected bone

0%

(4/897)

ML 1

Select Answer to see Preferred Response

PREFERRED RESPONSE 2

(SBQ07PE.38) An 8-year-old boy complains of left shoulder pain after a collision with his younger brother. He was asymptomatic prior to the incident. Which of the following treatments is most appropriate at this time? Review Topic

QID: 1523
FIGURES:
1

Aspiration and injection of methylprednisolone acetate

2%

(29/1218)

2

Open reduction, internal fixation

3%

(41/1218)

3

Initiation of radiation and chemotherapy

1%

(8/1218)

4

Immobilization in sling

92%

(1126/1218)

5

Radiofrequency ablation

1%

(9/1218)

ML 1

Select Answer to see Preferred Response

PREFERRED RESPONSE 4

(OBQ08.63) A 9-year-old child presents to your office after he felt a painful snap in his arm while throwing a baseball. He is otherwise in good health and has no family history of disease. A radiograph of his arm is shown in Figure A. What is the next step in your management? Review Topic

QID: 449
FIGURES:
1

Sling for comfort

84%

(1333/1581)

2

Tumor staging

2%

(24/1581)

3

Biopsy

11%

(172/1581)

4

Open reduction with internal fixation

2%

(31/1581)

5

Intramedullary nailing

1%

(15/1581)

ML 1

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PREFERRED RESPONSE 1

(OBQ05.144) A 7-year old boy experienced severe right hip pain following ice-skating. He previously had no hip pain and is otherwise healthy. Radiographs are shown in figures A and B. What is the recommended treatment ? Review Topic

QID: 1030
FIGURES:
1

Open biopsy and pathological staging without fracture fixation

8%

(122/1465)

2

Open reduction and internal fixation with bone grafting of the bone cyst

82%

(1197/1465)

3

Bedrest for 4 weeks followed by progressive weight-bearing as tolerated

3%

(41/1465)

4

Immediate hip spica casting

6%

(93/1465)

5

Tibial traction pin with 4 weeks of skeletal traction followed by open biopsy

1%

(8/1465)

ML 2

Select Answer to see Preferred Response

PREFERRED RESPONSE 2

(OBQ11.268) An 11-year-old boy presents with acute right arm pain after throwing a baseball. He is otherwise healthy and has no other complaints. Radiograph and CT scan of the lesion are shown in Figures A and B. What is the most appropriate treatment? Review Topic

QID: 3691
FIGURES:
1

Biopsy

8%

(133/1743)

2

Immobilization

89%

(1555/1743)

3

Intramedullary nailing and chemotherapy

1%

(25/1743)

4

Wide resection and radiation therapy

1%

(21/1743)

5

Amputation

0%

(4/1743)

ML 1

Select Answer to see Preferred Response

PREFERRED RESPONSE 2
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