Reactive lesions

Question 1

What are unicameral bone cysts?

Answer 1

• Aka simple bone cysts
• a non neoplastic, serous fluid bone lesion though to result from temporary failure of medullary bone formation near the physis
• pts <20 yrs
• location
  
  • proximal humerus- usually
  • prox fem, distal tibia, ilium, calcaneus, MC, distal radius
  • metaphysis adj to physis
  • progresses towards diaphysis w bone growth

Question 2

What is the prognosis of unicameral bone cysts?

Answer 2

• As pt approaches skeletal maturity bone cyst will
• decrease in size and may heal after growth complete
• fx healing doesn’t -> cyst resolution
• Follow up in active phase due to recurrence and risk of fx or growth arrest

Question 3

What are the classification of unicameral bone cysts?

Answer 3

• Active
  
  • if cyst is adjacent to physis
• Latent
  
  • if normal bone separates cyst from physis- see pic

Question 4

What are the symptoms of unicameral bone cysts?

Answer 4

• Aysymptomatic unless fx
• Pain from path fx -50%

Question 5

What is seen on radiographs with unicameral bone cysts?

Answer 5

• Central, lytic, well demarcated metaphyseal lesion
  
  • 2-3 % cross physis
• Cystic expansion w symmetrical thinning of cortices
• Fallen leaf sign - path fx with fallen cortical fragment in base of empty cyst
• MRI- v dark on T1, very bright T2
• Bone scan variable, usually warm

Question 6

What is seen on histology of unicameral bone cysts?

Answer 6

• Cyst with Thin fibrous lining containing fibrous tissue, giant cells and haemosiderin pigment

Question 7

What is the ddx if a unicameral bone cysts?

Answer 7

• Aneurysmal bone cyst
  
  • more expansile than UBC
  • UBC is usually not wider than physis
• Telangiectatic osteosarcoma

Question 8

What is the tx of unicameral bone cysts?

Answer 8

Non operative

• immobilzation alone
  
  • prox humeral path fx
  • 15% lesions will fill in w native bone after acute fx
• Aspiration/methylprednisolone acetate injection
  
  • active cysts in prox humerus
  • usually several injections esp in v young kids

Operative

• Currettage and bone grafting+/- internal fixation based on tumour location
  
  • latent cysts as risk of fx/osteonecrosis
  • prox femoral lesions- path fx-> high rate refx and malunion when tx nonop.
  • avoid in active lesions as communication w physis may-> growth arrst

Question 9

What is an aneurysmal bone cyst?

Answer 9

• A Benign and non neoplastic reactive bone lesion filled with multiple blood-filled cavities
• can be locally destructive to normal bone
• may extend into softt tissue
• 75% pts are <20 yrs
• location
  
  • ​25% spine
  • 20% long bones
  • usually Metaphysis
  • post elements of pelvis
• ​types
  
  • ​primary ABC
    
    • now known neoplasm due to upregualtion of ubiquitin-specific protease USP6 gene on 17p13
  • Secondary ABC
    
    • not neoplastic - no translocation

Question 10

Any associated conditions of aneurysmal bone cyst?

what is the prognosis of aneurysmal bone cyst?

Answer 10

• Assoc with Other tumours 30% time
• Giant cell tumour
• chondroblastoma
• fibrous dysplasia
• chondromyxoid fibroma
• NOF

Prognosis

• Good

Question 11

Describe the symptoms of aneurysmal bone cyst?

Answer 11

• Pain and swelling
• Path fx
• neurological deficit possible w spinal lesions

Question 12

What is seen on imaging of aneurysmal bone cyst

Answer 12

• Expansile, eccentric, lytic lesion with Bony septae= Bubby appearance
• Usually in metaphyseal bone
• thin rim perosteal new bone around lesion
• no matrix mineralisation
• MRI
  
  • multiple fluid lines - see pic
  • lesion can expand into soft tissue

Question 13

What is the histology of aneurysmal bone cyst?

Answer 13

• Cavernous space
• blood filled spaced without endothetial lining
• cavity lining
  
  • ​numerous benign giant cells
  • spindle cells

Question 14

What is the tx for aneurysmal bone cyst?

Answer 14

Non operative

• non operative fx management
  
  • ABC w acute fx
  • indicated until fx healed. once healed, tx as an ABC withouf fx, unless fx-> spontanous healing of ABC

Operative

• Aggressive curettage and bone grafting
  
  • symptomatic ABC without fx
  • some use adjuvant tx ( phenol)
  • local reoccurance up to 25%, more common in children w open physes