Aneurysmal Bone Cyst -

Definition

A benign cystic lesion of bone that expands the cortex.
It is the only bone lesion that derives its name from its X-ray appearance rather than its histology.
Term first used by Jaffe & Lichtenstein in 1942

primary (arise de novo)
secondary (arise in pre-existing tumours, frequently GCTs)
- More than 50% of ABCs arise from preexisting lesions

Unknown
Trauma may be related
nearly 1/2 are seen to occur in conjunction with another benign tumor and may represent a breakdown in the body’s reaction to the other tumor

Can involve any bone.
- 1. Proximal end of long bones
  - In long bones involves the metaphysis but can cross the growth plate.
- 2. Spine
  - In the spine involve the posterior elements (Differential Diagnosis here is osteoblastoma).
ABC is the commonest benign tumour of the clavicle

Pain
- usually mild and intermittent
- may be Rapid ↑ in pain
Swelling
- Swelling will tend to increase until the lesion is treated
Rarely, a pathologic fracture
Neurological
- If the lesion is located in the vertebral column, it may cause signs and symptoms of spinal cord compression (leg weakness, bowel or bladder dysfunction).

Expansile, multilocular balloon disrupting the adjacent bone & elevating the periosteum
- Most commonly, an area of lucency situated eccentrically in the medullary cavity of a long bone.
- Less commonly, may be situated centrally within the medulla.
- Much less commonly, may arise in the cortex or periosteum.
No matrix mineralization is present in the lesion
Most ABCs are completely lytic
ABCs may cross joints & involve several bones
- particularly in the spine where several adjacent vertebrae & ribs may be involved.
lesion tends to involve the cortex & may destroy it completely, when it may bulge out into the soft tissue where it usually forms a thin rim of calcification.
margins can be poorly or well defined; in half of cases the X-ray appearances suggest a benign process, & in a small number of cases they may suggest malignancy.
Periosteal new bone formation causing a buttress effect is characteristic.
There is no matrix calcification

internal septae & fluid levels with a layering effect.
Fluid levels (T2 weighted scans)
Finger in balloon sign
- preservation of a cortical cuff extending for a short distance into the expanded area of destructive blowout

Essential feature is cavernomatous spaces,
with walls that lack the normal features of blood vessels, such as muscle or elastic lamina
Thin strands of bone are often present in the fibrous tissues of the walls
septae almost invariably contain giant cells; this helps to distinguish from unicamerla bone cyst
Solid areas contain spindle cells that are loosely arranged
Chondroid like zones of calcification in solid portions of septae are commonly found & are relatively specific

ABCs are usually aggressive lesions associated with major bone destruction, pathological fractures & local recurrence
Spontaneous malignant transformation not recorded in the Mayo files but occurs very occasionally

Giant cell tumour
Giant cell reparative granuloma
Low-grade osteosarcoma
Telangiectatic osteosarcoma – probably most difficult Differential Diagnosis
- This disease is uncommon & rarely involves the vertebrae or small bones of the hands or feet
Renal cell carcinoma metastasis

May occur in other benign bone tumors or processes

Intralesional curettage & bone grafting & chemical cauterization of cyst walls
- treatment of choice
Lesions in expendable bones are excised
Preoperative Embolization
- If the lesion has a large soft tissue component or is large (>5-6cm) should consider preoperative embolization
- Especially pelvis, sacrum, vertebral bodies
Even incomplete resection may be followed by regression of the lesion
High recurrence rate
- Recurrence tends to occur within 6-18 months. It is very rare after 2 years.
- Recurrence rate is higher in spinal tumours
Radiotherapy
- has no role unless surgery is impossible.
- It used to be used adjuvantly but no longer is used to minimize the risk of sarcomatous transformation