Aneursymal bone cyst

Case contribution: Dr Radhiana Hassan


  • A 40 years old man
  • No known medical illness
  • Presented with painful swelling at left knee region
  • History of fall before the pain
  • Clinical examination shows mild swelling at tibial tuberosity which was tender on palpation. Limited knee movement due to pain. Small abrasion also noted over the left knee.
Plain radiograph of left tibia and fibula in AP and lateral views

X-Ray findings:

  • There is an expansile lytic lesion at proximal tibia (red arrows)
  • The lesion shows well-defined margin with narrow zone of transition
  • Multiple septa noted within the lesion
  • Thin sclerotic border is also seen
  • A cortical break is seen at anterior tibia (yellow arrow)
  • No soft tissue mass. No periosteal reaction.

Biopsy done shows:

  • Specimen labelled as blood consist of multiple pieces of brownish tissue measuring about 80 mm.
  • Features are compatible with osteoclastic giant cells rich lesion, differentials include aneurysmal bone cyst and giant cell tumour

Progress of patient:

  • Wide local excision with megaprosthesis fixation of proximal left tibia done

HPE findings:

  • Specimen labelled as left proximal tibia consists of proximal tibia, part of fibula and surrounding soft tissue and part of overlying skin.
  • Macroscopy: Cut sections of the tibia show a well-defined tumour, multiloculated, and composed of blood-filled, cystic spaces separated by tan-white, gritty septa measuring 75x80x55 mm. The fibula, surrounding soft tissue and skin are unremarkable.
  • Microscopy: sections from the tumour show a well circumscribed and contains blood-filled cystic spaces separated by fibrous septa. The fibrous septa are composed of a moderately dense, cellular proliferation of bland fibroblasts with scattered multinucleated, osteoclast-type giant cells and reactive woven bone rimmed by osteoblasts. In areas, hemorrhage and hemosiderin laden macrophages are seen. The fibula, adjacent tissue and skin are unremarkable. Negative for malignancy.
  • Interpretation: Aneurysmal bone cyst

Diagnosis: Aneursymal bone cyst


  • Aneurysmal bone cysts are a rare skeletal tumours that most commonly occurs in first two decades of lifer
  • They usually occur about the knee region but can occur in any axial or appendicular skeleton
  • It is typically eccentrically located in the metaphysis of long bones adjacent to unfused growth plate
  • Plain radiograph demonstrate a sharply demarcated expansile ostelytic lesions with thin sclerotic margins.
  • CT or MRI may demonstrate fluid-fluid levels.
  • Signal intensity are variables on MRI, presumably due to variable blood ages
  • Bone scan shows a ‘doughnut sign’- increased uptake peripherally with a photopenic center
Post operative radiograph
Author: radhianahassan