Aneurysmal bone cyst

Aneurysmal bone cyst is a benign osteolytic bone neoplasm characterized by blood filled spaces separated by fibrous septa. The term aneurysmal is mainly derived from its radiographic appearance.

Causes
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.

The lesion generally arises in 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.

It can be associated with a TRE17/USP6 translocation.

Effects
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.

Anatomy
The tumor can have an occurrence anywhere that there is bone. 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%)

Symptoms
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.

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

Treatment
Curettage is performed on some patients.