OrthoFracs Logo

Orthopaedic Tumour

Aneurysmal Bone Cyst

Definition

  • A benign cystic lesion of bone that expands the cortex.
  • It is the only bone lesion that derives its name from its X-ray appearance rather than its histology.
  • Term first used by Jaffe & Lichtenstein in 1942

Classification

  • primary (arise de novo)
  • secondary (arise in pre-existing tumours, frequently GCTs)
    • More than 50% of ABCs arise from preexisting lesions

Incidence

  • 2.5% of all primary bone tumours.
  • Half as frequent as giant cell tumours
  • M=F (perhaps slight female preponderance).
  • 76% in the first two decades of life
  • In contrast only 15% of patients with GCT are in the first two decades of life

Aetiology

  • Trauma may be related
  • Lichtenstein: intraosseous haemorrhage becoming an AV fistula or malformation

Localization

  • Some say most common around the knee, & the spine
  • Can involve any bone.
  • In long bones involves the metaphysis but can cross the growth plate.
  • In the spine involve the posterior elements (Differential Diagnosis here is osteoblastoma).
  • ABC is the commonest benign tumour of the clavicle

History

  • Pain & swelling. Rapid ↑ in pain
  • Rarely, a pathologic fracture

Examination

  • May be a mass or neurological symptoms if the spinal cord is compressed

Investigations

  • Xray
    • One way to think of the X-ray appearances of an ABC is to think of the lesion as an expansile, multilocular balloon disrupting the adjacent bone & elevating the periosteum
    • Most commonly, an area of lucency situated eccentrically in the medullary cavity of a long bone. Less commonly, may be situated centrally within the medulla. Much less commonly, may arise in the cortex or periosteum.
    • ABCs may cross joints & involve several bones, particularly in the spine where several adjacent vertebrae & ribs may be involved.
    • lesion tends to involve the cortex & may destroy it completely, when it may bulge out into the soft tissue where it usually forms a thin rim of calcification.
    • Most ABCs are completely lytic
    • margins can be poorly or well defined; in half of cases the X-ray appearances suggest a benign process, & in a small number of cases they may suggest malignancy.
    • Periosteal new bone formation causing a buttress effect is characteristic.
    • There is no matrix calcification
  • CT & MRI
    • may show internal septae & fluid levels with a layering effect. Fluid levels are best seen on T2 weighted scans
    • Finger in balloon sign
      • preservation of a cortical cuff extending for a short distance into the expanded area of destructive blowout

Pathology

Gross pathology

  • Red brown granular material, often in the form of curettings
  • operating surgeon frequently encounters what appears to a hole containing blood
  • blood in the lesion is not clotted, which some feel is evidence for an AVM, however there is no endothelial lining
  • pressure in an ABC may be elevated to arteriolar levels

Histology

  • Essential feature is cavernomatous spaces, with walls that lack the normal features of blood vessels, such as muscle or elastic lamina
  • Thin strands of bone are often present in the fibrous tissues of the walls
  • septae almost invariably contain giant cells; this helps to distinguish from SBC
  • Solid areas contain spindle cells that are loosely arranged
  • Chondroid like zones of calcification in solid portions of septae are commonly found & are relatively specific

Behaviour

  • ABCs are usually aggressive lesions associated with major bone destruction, pathological fractures & local recurrence
  • Spontaneous malignant transformation not recorded in the Mayo files but occurs very occasionally

Differential diagnosis (histology)

  • Giant cell tumour
  • Giant cell reparative granuloma
  • Low-grade osteosarcoma
  • Telangiectatic osteosarcoma – probably most difficult Differential Diagnosis
    • This disease is uncommon & rarely involves the vertebrae or small bones of the hands or feet
  • Renal cell carcinoma metastasis

Treatment

  • Intralesional curettage & bone grafting is the treatment of choice. In the Nov 2001 Mayo series a lower recurrence rate was noted with the use of phenol. Phenol is not used around nerve roots e.g. in sacral lesions
  • Lesions in expendable bones are excised
  • If the lesion has a large soft tissue component or is large (>5-6cm) should consider preoperative embolization
  • Even incomplete resection may be followed by regression of the lesion
  • There is a high recurrence rate. Recurrence tends to occur within 6-18 months. It is very rare after 2 years. The recurrence rate is higher in spinal tumours
  • Radiotherapy has no role unless surgery is impossible. It used to be used adjuvantly but no longer is used to minimize the risk of sarcomatous transformation

Prognosis

  • underlying lesion determines the prognosis of secondary ABC
  • May be an ↑ rate of recurrence in younger patients
  • The term aneurysmal relates to a sort of blowout distension of the contour of the bone & the term bone cyst relates to the fact that it represents mainly a blood filled cavity”
Bookmark and Share