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.
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