Friday, October 23, 2009

Aneurysmal Bone Cyst

Aneurysmal Bone Cyst
• Nonneoplastic vasocystic tumour
• Age group: 10-20 years old(peak age: 11 years)
• Can occur in any decade of adult life, but nearly 80% occur in the 2nd decade
• Represent 1.5% of all primary bone tumors
• Maybe primary or secondary( arising in other tumours)
• Frequency: distal femur> proximal tibia> proximal humerus> distal radius.
• The vertebrae are involved in 12% to 27% of patients
• Primary ABC maybe neoplastic. Chromosomal rearrangements suggestive of cancer like the USP6 and CDH11 are seen.
• Spontaneous regression may be seen in active primary ABCs. But rare in aggressive or secondary lesions
• May be of hydraulic pressure origin, secondary to haemorrhage and could be traumatically induced.
• Are not true cysts but rather sponge-like collections of interconnected fibrous tissue and blood-filled spaces
• Are destructive lesions and replace bone and thin the cortices of the host bone.
• In the spine, two-thirds of aneurysmal bone cysts will arise from posterior elements and one-third will arise from the vertebral body and present as an aggressive osteolytic lesion with extensive permeative cortical destruction.
• Children with open physes are much more prone to local recurrence (up to 50%)
• Pathological fractures are common and more frequent in humerus and femur

histology and classification

Campanacci’s classification of ABC (1)
1. Aggressive cyst: signs of reparative osteogenesis with ill-defined margins and no periosteal shell.
2. Active cyst: has an incomplete periosteal shell and a defined margin between the lesion and the host bone.
3. Inactive cyst: has a complete periosteal shell and a sclerotic margin between the cyst and the long bone.


• Composed of blood filled spaces with intervening fibrous septae. True endothelial cells are not found.
• The tissue is sponge like with cavernous spaces filled with blood.
• Cavities surrounded by gray or brownish tissue with an osseous component
• At the periphery of the lesion is an eggshell-like layer of periosteal bone around the lesion
• Solid variant of ABC consist of fibrous or granular tissue with local haemorrhages and a layer of reactive bone.
• There are skeletal tumours that may demonstrate an aneurysmal component: Giant cell tumour, chondroblastoma, osteoblastoma, chondromyxoid fibroma, fibrous dysplasia, and malignant haemorrhagic osteosarcoma

X rays:
– Eccentrically (maybe central also) located lytic lesion, expansile with septations.
– Classically, blown out cortex with egg-shell thin rim of reactive bone
– Sites: metaphysis of long bone, posterior elements of spine, distal phalanx of fingers
– Fluid levels can be seen on MRI /CT scans, which may also be seen with telengiectatic osteosarcoma

Useful to assess lesions of the pelvis or vertebral column more precisely than radiography
Helps to assess carefully the presence of the periosteal rim of bone around a lesion

‣ can evaluate soft tissue involvement
‣ On T2-weighted images, the lesions have high signal levels, and layering in the blood (fluid-fluid levels) often can be seen
‣ more accurate assessment than CT or radiography of the extent of an aneurysmal bone cyst

Differential Diagnosis for Holes in Bone: (Mnemonic: FOGMACHINE)
Fibrous dysplasia
Osteoid osteoma, Osteoblastoma,Osteosarcoma, Osteofibrous dysplasia
Giant cell tumor
Aneurysmal bone cyst, adamantinoma
Chondromyxoid fibroma, chondroblastoma, chondrosarcoma
Nonossifying fibroma
Enchondroma, Ewing sarcoma

– Augmented curettage and bone grafting.
– Repeated embolisation to reduce the rate of haemorrhagic expansion especially in difficult areas like the pelvis
– Pathologic fractures: require curettage , bone grafting +/- stabilisation
– Pelvic ABCs: spontaneous regression after biopsy has been noted. Consider observation after biopsy. If regression occurs no need for further surgery. If progression occurs, perform curettage
– Spinal ABCs: preoperative selective arterial embolisation, extended intralesional curettage with grafting +/- limited fusion. Embolisation though poses risk of cerebral emboli and also ischemic damage to the cord
– Incompletely resectable, recurrent or aggressive ABCs: low dose radiation(26 to 30 cGy)
– If a patient does have a local recurrence, repeat surgical excision can be performed.
– Selective arterial embolisation as a definitive procedure can be used in locations where a tourniquet cannot be used and control of bleeding can become difficult (e.g., spine, pelvis, and the proximal portions of the extremities)(2)

1. Campanacci M, Capanna R, Picci P. Unicameral and aneurysmal bone cysts. Clin Orthop 1986; 204:25-36.
2. Green JA, Bellemore MC, Marsden FW. Embolization in the treatment of aneurysmal bone cysts. J Pediatr Orthop 1997;17(4):440-443.

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