Aneurysmal bone cyst , abbreviated ABC , is an osteolytic bone neoplasm characterised by several sponge-like blood or serum filled, ordinarily non- endothelialized spaces of numerous diameters.

Etymology

The term is a misnomer, as the lesion is neither an aneurysm nor a cyst .

Causes

Aneurysmal bone cyst has been widely regarded a reactive process of uncertain aetiology after its initial description by Jaffe and Lichtenstein in 1942. Many hypotheses have been proposed to explain the aetiology and pathogenesis of aneurysmal bone cyst, and until quite recently the most commonly accepted idea was that aneurysmal bone cyst was the consequence of an increased venous pressure and resultant dilation and rupture of the local vascular network. Notwithstanding studies by Panoutsakopoulus et al. and Oliveira et al. uncovered the clonal neoplastic nature of aneurysmal bone cyst. Primary aetiology has been regarded arteriovenous fistula within bone.

The lesion might arise de novo or might arise secondarily within a pre-existing bone tumor, because the abnormal bone causes changes in hemodynamics . An aneurysmal bone cyst can arise from a pre-existing chondroblastoma , a chondromyxoid fibroma , an osteoblastoma , a giant cell tumor , or fibrous dysplasia . A giant cell tumour is the most common cause, occurring in nineteen percent to 39 percent of cases. Less frequently, it results from a few malignant tumors, like osteosarcoma , chondrosarcoma , and hemangioendothelioma .

Pathology

Histologically, they're classified in two variants.

  • The classic (or standard) form (95%) has blood filled clefts amongst bony trabeculae. Osteoid tissue is found in stromal matrix.
  • The solid form (5%) shows fibroblastic proliferation, osteoid production and degenerated calcifying fibromyxoid elements.

According to Buraczewski and Dabska, the development of the aneurysmal bone cyst follows three stages.

Stage Description
Initial phase (I) Osteolysis without peculiar findings
Growth phase (II)
  • Rapid increase in size of osseous erosion
  • Enlargement of involved bone
  • Formation of shell around central part of lesion
Stabilization phase (III) Fully developed radiological pattern

They can additionally be associated with a TRE17 / USP6 translocation. [3]

Aneurysmal bone cysts might be intraosseous, staying inside of the bone marrow. Or they might be extraosseous, developing on the surface of the bone, and extending into the marrow. A radiograph will reveal a soap bubble appearance.

Clinical features

The afflicted might have relatively small amounts of pain that will increase in severity over a time period of 6–12 weeks. The skin temperature around the bone might increase, a bony swelling might be evident, and movement might be restricted in adjacent joints. [7]

Spinal lesions might cause quadriplegia and patients with skull lesions might have headaches.

Sites

Commonly affected sites are metaphyses of vertebra , flat bones , femur and tibia . Approximate percentages by sites are as shown:

  • Skull and mandible (4%)
  • Spine (16%)
  • Clavicle and ribs (5%)
  • Upper extremity (21%)
  • Pelvis and sacrum (12%)
  • Femur (13%)
  • Lower leg (24%)
  • Foot (3%)

Diagnosis

On a radiograph, well-defined, expansile, lytic lesion is observed. Expansion of cortex gives the lesion a balloon-like appearance. Larger lesions might appear septated

Differential diagnosis

Following conditions are excluded before diagnosis can be confirmed:

  • Unicameral bone cyst
  • Giant cell tumor
  • Telangiectatic osteosarcoma
  • Secondary aneurysmal bone cyst

Treatment

Curettage is performed on a few patients, [10] and is sufficient for inactive lesions. The recurrence rate with curettage is significant in active lesions, and marginal resection has been advised. Liquid nitrogen , phenol , methyl methacrylate are considered for use to kill cells at margins of resected cyst.

Prognosis

Recurrence rate of solid form of tumour is lower than classic form.

Epidemiology

It is common in age group of 10–30 years. It is second most common tumour of spine and commonest benign tumour of pelvis in pediatric population. Incidence is slightly more in males than females (1.3:1).

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