Aneurysmal Bone Cyst

 

Aneurysmal Bone Cyst (ABC) is a non malignant, tumour like vascular and reactive malformation comprised of blood filled channels

It is usually a single, expansive and aggressive lesion.

Incidence

  • 1-6 % of primary bone tumours

Age Predilection

  • It is most commonly seen in the age group of 15-25 years, but can be found in any age.

Location

  • It is found in the metaphysis and epiphyseal of long bones (upper extremity > lower extremity)
  • Pelvis, spine uncommon (large volume disease often)

What is the cause of ABC?

  • Etiology is
  • It is suspected to be related to trauma.
  • As a Primary Tumour
  • It is also found as a secondary component of other tumors such as:
    • Giant cell tumor
    • Chondroblastoma
    • Fibrous dysplasia
    • Osteoblastoma
    • CHondromyxoid FIbroma
    • Osteosarcoma & CHondrosarcomas
  • Specific translocations of the TRE17/USP6 gene [due to t(16,17) translocation and upregulation which halts osteoblastic maturation] are reported in about 70% of primary ABC but never in secondary ABC lesions

How is ABC identified?

  • Pain, dull aching.
  • Swelling of several weeks
  • Pathological fracture is common due to the aggressive nature
  • Occasionally, neurological symptoms if lesion is pressing on spinal cord

Imaging

  • Plain radiographs show a solitary, expanded cavity with cystic or osteolytic lesion, with thin “eggshell” sclerotic borders.

The enclosed cavity contains many dividing septa.

The surrounding bone may be pushed outwards from its normal anatomy, demonstrating the aggressive, expansile nature of the lesion (Soap-Bubble).

  • MRI is necessary to diagnose ABC, and the typical finding is Multiple Fluid-Fluid levels on T1 contrast and T2 weighted images.
  • CT is not done often. May show egg-shell rim with fluid fluid levels with contrast
  • Biopsy (Needle) is mandatory to diagnose ABC as it can mimic any of the other benign or even malignant bone tumors.
  • Pathological examination shows blood filled cyst cavities with giant cells, spindle cells, fibroblasts without atypia.

How is ABC treated?

Treatment of ABC depends upon location and aggressiveness of lesions.

Very few ABC’s can be in latent or inactive stage, not needing any intervention.

Treatment options are as follows:

  • Minimally Invasive- Image Guided
    • Percutaneous curettage (Curopsy)
    • Percutaneous Sclerotherapy (polidocanol, 3 % aethoxysklerol) under radiological guidance
    • Usually needs to be repeated at 2-3 month intervals, with average healing time of 5 months.
  • Surgery
    • Extended Curettage to clear tumor followed by filling or reconstruction of the defect with bone grafts similar to GCT.
    • Adjuvants can be used, but there is no clear evidence of benefit.
  • Alternate Treatment Strategy OR Combination Strategy in Large SIze OR Axial OR Inoperable Situations.

Percutaneous Serial Arterial Embolization can be carried out with aid or Interventional Radiologist with good results to decrease the size of tumor

  • Recently, there has been a shift in treating ABC’s by minimally invasive surgical procedures like Curopsy and/or Sclerotherapy, due to similar results noted between surgical and minimally invasive procedures.
  • In some situations, when the tumour has grown so large, resulting in pathological fracture or when the bone is not salvageable, a resection and reconstruction procedure (biological or Tumor endoprosthesis) is carried out.

Does ABC reappear?

  • The recurrence rate in long bones after curettage alone is 20-35 % which can be reduced by performing extended curettage resulting in risk of local recurrence at 10%
  • Similar rates of recurrence are being observed when ABC’s are being treated by Curposy and/or Sclerotherapy.
  • ABC is aggressive and may add to morbidity.
  • It does not metastasize and is not fatal.
  • Adjuvant treatment with Zoledronic acid or Denosumab is encouraging but has limited scientific data.

 

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