by Jason Wasserman MD PhD FRCPC
March 1, 2024
An aneurysmal bone cyst (ABC) is a benign (noncancerous) but locally aggressive bone lesion that typically affects children and young adults. Characterized by blood-filled spaces separated by connective tissue, aneurysmal bone cysts can cause significant bone expansion and weakening. They most commonly occur in the long bones of the legs, the vertebrae, and the flat bones, such as those of the pelvis.
Patients with an aneurysmal bone cyst may experience a range of symptoms, often depending on the cyst’s location and size. Common symptoms include localized pain and swelling, which may be accompanied by a noticeable lump or mass. If the cyst is located near a joint, decreased range of motion or stiffness may occur. In cases where the spine is involved, neurological symptoms such as numbness, tingling, or weakness in the limbs can arise due to compression of spinal nerves or the spinal cord itself.
The exact cause of aneurysmal bone cysts remains under investigation, but they are thought to result from a combination of genetic factors and prior trauma. Some evidence suggests that aneurysmal bone cysts may develop in response to an underlying bone lesion or after minor injuries that lead to local circulatory changes. For these reasons, aneurysmal bone cyst-like changes are commonly found in the tissue surrounding bone tumours. Genetic mutations have also been identified in some cases, indicating a potential molecular mechanism behind their development. These mutations can lead to abnormal blood vessel formation and bone resorption, contributing to the cyst’s growth.
Under the microscope, an aneurysmal bone cyst has a unique appearance. The lesion is composed of blood-filled cavities or spaces, which are not lined by endothelial cells (the cells typically lining blood vessels). These cavities are separated by septa or walls made up of fibrous tissue, osteoid (newly formed bone tissue), and osteoclast-like giant cells. The septa often contain trabeculae of woven bone with areas of osteoblastic activity, indicating bone formation. The presence of multinucleated giant cells and areas of recent and old hemorrhage within the septa are also characteristic features. These microscopic findings are crucial for distinguishing aneurysmal bone cysts from other bone lesions and ensuring accurate diagnosis and treatment planning.
Doctors wrote this article to help you read your pathology report and understand your diagnosis. Contact us if you have any questions about this article or your pathology report.