Aneurysmal bone cyst of left lamina of T1 vertebra.
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.
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 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.
- 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 spinal canal, adjacent ribs, and paravertebral soft tissues.