Introduction
Background
An aneurysmal bone cyst is an expansile osteolytic lesion with a thin wall, containing blood-filled cystic cavities. The term aneurysmal is derived from its radiographic appearance.
Pathophysiology
Trauma is considered an initiating factor in the pathogenesis of some cysts in well-documented cases involving acute fracture. Local hemodynamic alterations related to venous obstruction or arteriovenous fistulae that occur after an injury are important in the pathogenesis of an aneurysmal bone cyst.
The lesion is a component of, or arises within, a preexisting bone tumor in about one third of cases; this finding further substantiates the fact that aneurysmal bone cysts occur in an abnormal bone as a result of associated hemodynamic changes. An aneurysmal bone cyst can arise from a preexisting chondroblastoma, a chondromyxoid fibroma, an osteoblastoma, a giant cell tumor, or fibrous dysplasia. Less frequently, it results from some malignant tumors, such as osteosarcoma, chondrosarcoma, and hemangioendothelioma.
Aneurysmal bone cysts may be purely intraosseous, arising from the bone marrow cavity. In this case, they are primarily cystic and slowly expand into the cortex. They may be extraosseous, arising from surface of bones, eroding adjacent cortex, and extending into the marrow space.
Four phases of pathogenesis are recognized, as follows:
- Osteolytic initial phase
- Active growth phase, which is characterized by rapid destruction of bone and a subperiosteal blow-out pattern
- Mature stage, also known as stage of stabilization, which is manifested by formation of a distinct peripheral bony shell and internal bony septae and trabeculae that produce the classic soap-bubble appearance.
- Healing phase with progressive calcification and ossification of the cyst and its eventual transformation into a dense bony mass with an irregular structure.
Race
No specific racial distribution has been identified.
Sex
Compared with males, females have an increased incidence.
Age
Aneurysmal bone cysts may occur in patients aged 10-30 years, with a peak incidence in those aged 16 years. About 75% of patients are younger than 20 years.
Anatomy
Regarding the location of the lesions, any bone may be affected. Approximate frequencies by site are shown below:
- Skull and mandible (4%)
- Spine (16%)
- Clavicle and ribs (5%)
- Upper extremity (21%)
- Pelvis and sacrum (12%)
- Femur (13%)
- Lower leg (24%)
- Foot (3%)
The most common site is the metaphyseal region of the knee.
Short tubular bones are less frequently affected and are involved in about 10% of cases.
Spinal involvement demonstrates a predilection for the posterior elements. In decreasing order of frequency, the following parts of the spine are involved: cervical, thoracic, lumbar. Contiguous vertebrae may be involved in 25% of cases.
The cyst involves the diaphysis in isolation in about 8% of cases.
Presentation
The clinical manifestation depends on the specific site of involvement. A common presentation includes pain of relatively acute onset that rapidly increases in severity over 6-12 weeks.
The local skin temperature may increase, a palpable bony swelling may be present, and movement in an adjacent joint may be restricted.
Spinal lesions may cause neurologic radiculopathy or quadriplegia, and patients with skull lesions may have moderate to severe headaches.
Preferred Examination
Radiographs usually are adequate for diagnosis. Cross-sectional imaging may be required when lesions are in unusual locations, such as the axial skeleton.
Limitations of Techniques
Radiographs usually are adequate for characterizing typical lesions; however, sometimes, the exclusion of fractures or complications from the lesion is difficult.
Differential Diagnoses
Enchondroma and Enchondromatosis
Giant Cell Tumor
Hyperparathyroidism, Primary
Osteoblastoma
Other Problems to Be Considered
Brown tumors in hyperparathyroidism
Expansile metastasis from renal cell carcinoma and thyroid carcinoma
Hemophilic pseudotumor with hemorrhage
Infestation of bone by a hydatid cyst
Telangiectatic osteosarcoma
More on Aneurysmal Bone Cyst |
 Overview: Aneurysmal Bone Cyst |
| Imaging: Aneurysmal Bone Cyst |
| Follow-up: Aneurysmal Bone Cyst |
| References |
| Next Page » |
References
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Further Reading
Keywords
blood-filled expansile osteolytic lesion, preexisting chondroblastoma, chondromyxoid fibroma, osteoblastoma, giant cell tumor, fibrous dysplasia, osteosarcoma, chondrosarcoma, hemangioendothelioma
