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oncology

Aneurysmal Bone Cyst (ABC)

intermediate
6 min
28 marks
6 questions
Clinical Scenario
A 14-year-old girl presents with 3 months of progressive right knee pain and swelling. She denies trauma or constitutional symptoms. On examination, there is a firm, non-tender swelling over the proximal tibia with no warmth or erythema. X-ray shows an eccentric, expansile lytic lesion in the proximal tibial metaphysis with a thin cortical shell. MRI demonstrates multiple fluid-fluid levels within the lesion.
Axial T2-weighted MRI of the proximal tibia demonstrating an aneurysmal bone cyst (ABC). The lesion shows characteristic multiloculated appearance with multiple fluid-fluid levels representing blood products of different ages. The lesion is eccentric and expansile with a thin cortical shell. No solid component is seen, which would raise concern for secondary ABC from underlying malignancy.
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Axial T2-weighted MRI of the proximal tibia demonstrating an aneurysmal bone cyst (ABC). The lesion shows characteristic multiloculated appearance with multiple fluid-fluid levels representing blood products of different ages. The lesion is eccentric and expansile with a thin cortical shell. No solid component is seen, which would raise concern for secondary ABC from underlying malignancy.

Image source: Open Access medical literature (NIH/PubMed Central) • CC-BY License

Questions

Question 1 (4 marks)

Describe the clinical and radiographic features of aneurysmal bone cyst.

Question 2 (5 marks)

What is the pathophysiology and classification of ABC?

Question 3 (6 marks)

Describe the treatment options and surgical technique.

Question 4 (5 marks)

What are the differential diagnoses and how do you distinguish them?

Question 5 (4 marks)

Discuss ABC of the spine.

Question 6 (4 marks)

What are the outcomes and complications?

Exam Day Cheat Sheet

Must Mention

  • •Age 10-20, slight female predominance
  • •Eccentric metaphyseal, expansile
  • •Fluid-fluid levels on MRI (pathognomonic)
  • •Primary (USP6) vs secondary (30-50%)
  • •Rule out telangiectatic osteosarcoma
  • •Curettage + adjuvant = 80-90% success

Common Pitfalls

  • •Confusing with UBC
  • •Missing secondary ABC
  • •Not ruling out telangiectatic OS
  • •Wrong recurrence rates
  • •Missing fluid-fluid levels
  • •Forgetting adjuvant treatment