Aneurysmal bone cyst


  • A 26 years old lady
  • Right distal thigh swelling for one year
  • Recent increase in size
  • Associated with dull pain on and off
  • Worsening of pain upon prolong ambulation
  • No constitutional symptoms
  • Clinically examination shows a mass over medial aspect of distal femur about 8×6 cm, bony hard and non-mobile, not attached to skin. No skin changes.
Radiograph of right knee in AP and lateral views

Radiographic findings:

  • There is an expansile lytic lesion at metaphysis of distal femur
  • It showed narrow zone of transition, No obvious sclerotic margin
  • Thinning of the cortex
  • “soap-bubble” appearance seen
  • No fracture
  • No obvious soft tissue swelling
  • No extension to articular surface
  • No periosteal reaction

MRI in axial plane; (A) T1WI, (B) T2WI and (C) T1+Gadolinium

MRI findings:

  • A well defined fairly round lesion noted at distal right femur. The lesion measure 3.8 x 4.7 x 4.6cm (APxWxCC). It is located about 1 cm from knee joint.
  • The lesion appears hypointense on T1, hyperintense on T2 and not suppressed on FLAIR.
  • It has well defined irregular margin which appear hypointense on T1 and T2WI.
  • Multiple thin septation within which enhanced post contrast. The peripheral of the lesion also enhanced post contrast.
  • Fluid-fluid level noted (red arrow).
  • Normal signal of bone marrow surrounding the lesion. No cortical break or periosteal reaction. Surrounding muscles are normal. The neurovascular bundle is intact.

HPE findings:

  • Macroscopy: specimens labelled as bone and cyst aspirate.
  • Microscopy: Section of bone specimen shows fragmented unremarkable bony trabeculae and marrow spaces, admixed with a fragment of fibro-collagenous tissue. The marrow spaces are consist of fatty tissue and normal hematopoietic cells. The fibro-collagenous tissue are composed of bland fibroblast proliferation, aggregates of cholesterol clefts and occasional multinucleated giant cells. In areas, hemosiderin laden macrophages are also noted. Negative for malignancy.
  • Section of tissues from cyst aspirate shows predominantly blood admixed with tiny fragments of fibro-collagenous. The fibro-collagenous tissue are composed of bland fibroblasts proliferation and scattered multlinucleated giant cells. In areas, hemosiderin laden macrophages are also noted. Negative for malignancy.
  • Interpretation: compatible with aneurysmal bone cyst

Diagnosis: Aneurysmal bone cyst


  • Aneurysmal bone cysts are benign expansile tumor-like bone lesions of uncertain etiology mostly diagnosed in children and adolescents
  • Peak age 16 years; range from 10-30 years, in 75% <20 years
  • Female>Male
  • Location
  • Spine: 12-30%, predilection for posterior elements. Thoracic>lumbar>cervical spine
  • Long bones: eccentric in metaphysis of femur, tibia, humerus, fibula
  • Radiographic features include:
    • Purely lytic eccentric radiolucency
    • Aggressive expansile ‘soap-bubble’ pattern with internal trabeculations
    • Sclerotic inner portion
    • Almost invisible thin cortex
    • Tumour respect epiphyseal plate
    • No periosteal reaction
  • CT shows blood-filled sponge with fluid-fluid levels
  • MRI shows
    • multiple cysts of different signal intensity representing different stages of blood products
    • Low signal intensity rim = intact thickened periosteal membrane
  • Angio: hypervacularity in lesion periphery in 75%
  • Bone scan: ‘doughnut sign’= peripheral increased intake and a photophenic centre

Progress of patient:

  • Planned for extended curretage, bone cement and locking plate distal right femur



Author: radhianahassan