Aneurysmal bone cyst
|Aneurysmal bone cyst|
|Classification and external resources|
The ABC is located on the left, on the fifth metatarsal. Notice that the bone appears to be missing on the x-ray.
Aneurysmal bone cyst has been widely regarded a reactive process of uncertain etiology since its initial description by Jaffe and Lichtenstein in 1942. Many hypotheses have been proposed to explain the etiology and pathogenesis of aneurysmal bone cyst, and until very 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. However, studies by Panoutsakopoulus et al. and Oliveira et al. uncovered the clonal neoplastic nature of aneurysmal bone cyst. Primary etiology has been regarded arteriovenous fistula within bone.
The lesion may arise de novo or may arise secondarily within a pre-existing bone tumor, this is because of the abnormal bones 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 tumor is the most common cause, occurring in 19% to 39% of cases. Less frequently, it results from some malignant tumors, such as osteosarcoma, chondrosarcoma, and hemangioendothelioma.
Histologically, they are classified in two variants.
- The classic (or standard) form (95%) has blood filled clefts among 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.
|Initial phase (I)||Osteolysis without peculiar findings|
|Growth phase (II)||
|Stabilization phase (III)||Fully developed radiological pattern|
Aneurysmal bone cysts may be intraosseous, staying inside of the bone marrow. Or they may be extraosseous, developing on the surface of the bone, and extending into the marrow.
The afflicted may have relatively small amounts of pain that will quickly increase in severity over a time period of 6–12 weeks. The skin temperature around the bone may increase, a bony swelling may be evident, and movement may be restricted in adjacent joints.
- Skull and mandible (4%)
- Spine (16%)
- Clavicle and ribs (5%)
- Upper extremity (21%)
- Pelvis and sacrum (12%)
- Femur (13%)
- Lower leg (24%)
- Foot (3%)
On a radiograph, well-defined, expansile, lytic lesion is observed. Expansion of cortex gives the lesion a balloon-like appearance. Larger lesions may appear septated
Following conditions are excluded before diagnosis can be confirmed:
- Unicameral bone cyst
- Giant cell tumor
- Telangiectatic osteosarcoma
- Secondary aneurysmal bone cyst
Curettage is performed on some patients, 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.
Recurrence rate of solid form of tumour is lower than classic form.
It is common in age group of 10-30 years. It is second most common tumor of spine and commonest benign tumor of pelvis in pediatric population. Incidence is slightly more in males than females (1.3:1).
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