Aneurysmal bone cyst
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Aneurysmal Bone Cysts (ABCs) most commonly occur during the 1st and 2nd decades, with a peak incidence at age 13. 75% of cases occur prior to age 20. There is a predilection for female > male patients. ABCs tend to occur in the metaphysis of long bones, and involves the spine 16% of all cases, and the cranium 4% of all cases.
Onset tends to be insidious, with pain as the primary symptom. The pain tends to be a deep ache, which progresses significantly over 6-12 weeks. If the neural arch is involved, radiculopathy followed by myelopathy or cauda equina may develop. Calvarial ABCs most often present with headaches, and a palpable, warm fixed mass under the scalp.
- Plain films often demonstrate an expansile, "bubbly" mass.
- On CT, the most common finding is the absent pedicle sign in spinal involvement.
- MRI demonstrates a heterogenously enhancing, bubbly soft tissue mass, highly vascular, which may have fluid-fluid levels.
- Angiography is often negative. However, selective injection can demonstrate feeders, which are often embolized when possible prior to resection.
Grossly, ABCs appear as a beefy red mulberry like lesion, and are composed of of multiple blood filled cells with fibrous septae. On H&E section, the blood filled cystic component is visible. The cysts are often lined with multi-nucleate osteoclast-like cells.
Complete excision is curative. Depending on the size and location of the mass, resection may be followed by reconstruction and/or stabilization. When available, pre-embolization of the feeder arteries will reduce the often large blood volume losses during surgery. Radiation results are limited, and radiosurgery should 'not be considered primary treatment. Recurrence rate is 10-25%.