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Radiology > MUSCULOSKELETAL
Aneurysmal Bone Cyst
Article Last Updated: Apr 3, 2007
AUTHOR AND EDITOR INFORMATION
Section 1 of 11  
Author: Mahesh Kumar Neelala Anand, MBBS, DNB, FRCR, Clinical Director, Consultant Radiologist, Department of Radiology, Pennine Acute Hospitals NHS Trust, Manchester, UK
Mahesh Kumar Neelala Anand is a member of the following medical societies: British Medical Association, Radiological Society of North America, and Royal College of Radiologists
Coauthor(s):
Eric A Wang, MD, Consulting Staff, Department of Radiology, Carolinas Medical Center
Editors: Michael A Bruno, MD, Associate Professor, Departments of Radiology and Medicine, Pennsylvania State University College of Medicine; Director, Radiology Quality Management Services, Milton S Hershey Medical Center, Pennsylvania State University College of Medicine; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; Murali Sundaram, MBBS, FRCR, FACR, Consulting Staff, Department of Diagnostic Radiology, The Cleveland Clinic Foundation; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Felix S Chew, MD, EdM, MBA, Professor, Department of Radiology, Section Head of Musculoskeletal Radiology, Vice Chairman for Radiology Informatics, University of Washington
Author and Editor Disclosure
Synonyms and related keywords:
blood-filled expansile osteolytic lesion, preexisting chondroblastoma, chondromyxoid fibroma, osteoblastoma, giant cell tumor, fibrous dysplasia, osteosarcoma, chondrosarcoma, hemangioendothelioma
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.
Clinical Details
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.
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
Findings
Tubular bones
The classic description of an aneurysmal bone cyst includes an eccentric radiolucency and a purely lytic or, occasionally, trabecular process, with its epicenter in the metaphysis of an unfused long bone.
The trabeculae in the cyst may create a soap-bubble appearance in the lesion.
The margins of the lesion are well defined, with a smooth inner margin and a rim of bone sclerosis. The tumor does not usually extend into the epiphyseal plate until after complete fusion, when it may occasionally do so. The expansion or ballooning of the cortex occasionally may result in the loss of the sharp definition of its margin. In this case, the finding should correctly be interpreted as an aggressive lesion rather than as solely diagnostic of malignant change.
New bone may horizontally traverse the angle between the original cortex and the expanded part of the bone; this occurs because the periosteum is lifted. No periosteal reaction occurs, except when the periosteum is fractured.
Spine
Typically, the spinal lesion is osteolytic, with a predilection for the posterior elements. The lesion may involve the lamina, arches, pedicles, or spinous processes, with or without extension into the vertebral body. The lesion may extend into the adjacent vertebral body, violating the intervertebral disk and causing vertebral collapse and/or extension into the spinal canal, adjacent ribs, and paravertebral soft tissues.
Other locations
As in the innominate bones, flat bones have osteolysis with an expansile lesion.
Expanded bone may displace the adjacent viscera, such as the urinary bladder, when occurring in the pelvis.
Lesions in the skull have osteolysis, with expansion of both inner and outer tables with intracranial extension.
Mandibular and maxillary lesions are multilocular, expansile, and osteolytic. They predominate in the region of the molar teeth.
Aneurysmal bone cysts are difficult to distinguish from malignant lesions in some locations. It may mimic a sarcoma in the ribs, scapula, or sternum, especially when associated with a large soft-tissue component.
CT may be necessary to define the extent of involvement before surgery or other treatment.
Degree of Confidence
The accuracy of radiography is high, especially with lesions in the appendicular skeleton. Cross-sectional imaging may be useful in defining the extent of spinal, thoracic cage, and pelvic bone involvement. Cross-sectional imaging may not increase the specificity to a large extent.
Findings
Cross-sectional CT is the most useful imaging examination, because it can demonstrate the intraosseous and extraosseous extents of the lesion. CT can be used to determine the nature of the matrix of the tumor, especially when tumors are in complex locations, such as the facial skeleton, spine, thoracic cage, and pelvis.
Fluid-fluid levels may be seen in the cysts. Fluid levels are depicted only when the patient is lying motionless for about 10 minutes and when the scans are obtained in the plane perpendicular to that of the fluid levels. Fluid-fluid levels also are seen in many other bone lesions, and this finding is not specific to aneurysmal bone cysts. These levels may be seen in malignant and benign lesions, such as giant cell tumors, and in telangiectatic osteosarcomas.
CT in the spine can demonstrate stenosis of the spinal canal due to involvement of the posterior elements.
Degree of Confidence
The extent of the disease can be estimated better with CT than with plain radiography. The specificity is slightly increased when fluid levels are depicted, but the fluid levels may be present in many other conditions.
Findings
T1-weighted images show predominantly low to intermediate signal intensity with or without fluid levels. Acute hemorrhage into the cyst may have high signal intensity. T2-weighted images show areas of low to intermediate signal intensity or some areas of heterogeneous high signal intensity, depending on the contents of the cyst. A rim of low signal intensity with internal septa may produce a multicystic appearance. MRI images of aggressive lesions show tumor enhancement with gadolinium enhancement, especially when they are associated with other tumors. Spinal cord compression and signal-intensity alteration in the cord can be evaluated when neurologic symptoms are present. Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have recently been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans. As of late December 2006, the FDA had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble movingor straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape.
Findings
No significant role has been established for ultrasonography in the diagnosis of aneurysmal bone cysts.
Findings
Radioisotope uptake is increased. The common pattern is the accumulation of the tracer in the periphery of the lesion, with little intensity in the center. This finding is present in about 65% of cases.
The appearance of the lesion is nonspecific, with no correlation of isotopic activity to lesional size, shape, contents, osteoblastic activity, or identifiable histologic abnormality.
Degree of Confidence
The specificity is poor. Demonstration of a solitary lesion on bone scintigraphy helps to distinguish an aneurysmal bone cyst from a brown tumor, a hemophilic pseudotumor, etc.
Findings
On angiograms, aneurysmal bone cysts are hypovascular lesions with a hypervascular localized region. This feature is contrary to that of other malignant lesions such as osteosarcoma and chondrosarcoma, which have gross hypervascularity.
Hypervascular regions in aneurysmal bone cysts may affect the prognosis, because the number and size of the lesions are positively correlated with the likelihood of lesional recurrence after treatment.
Special Concerns
- The solid variant is a recently identified variant of aneurysmal bone cysts.
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- This variant has a predilection for the axial skeleton and occurs in persons aged 20 years or younger.
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- They have a variable radiologic appearance, which ranges from that of a completely cystic aneurysmal bone cyst to a moth-eaten appearance with cortical destruction and soft-tissue extension.
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Aneurysmal Bone Cyst excerpt Article Last Updated: Apr 3, 2007
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