Aneurysmal bone cysts (ABCs) are benign, blood-filled bone lesions that can cause bone expansion and destruction. They are not cancerous but can behave aggressively by growing and weakening the affected bone. The exact cause of aneurysmal bone cysts is not fully understood, but several factors and mechanisms are believed to contribute to their development.
One key factor is that ABCs often arise due to a localized disturbance in the bone’s blood vessels. This disturbance leads to the formation of multiple blood-filled spaces or cysts within the bone. These cystic spaces expand over time, causing the bone to swell and thin out. The expansion is driven by increased pressure from the blood pooling inside these cystic cavities, which can erode the surrounding bone tissue.
Genetic changes also appear to play a role. Many ABCs show specific chromosomal abnormalities, particularly involving rearrangements of the USP6 gene. These genetic alterations may trigger abnormal cell growth and increased blood vessel formation within the bone, contributing to cyst formation and expansion. This suggests that ABCs can be considered a type of benign tumor driven by genetic mutations, although they are not malignant.
In some cases, aneurysmal bone cysts develop secondary to other bone lesions or tumors. For example, they may arise in association with giant cell tumors, chondroblastomas, or fibrous dysplasia. In these situations, the primary lesion may cause local bone damage and bleeding, which then leads to the formation of the cystic blood-filled spaces characteristic of ABCs. This secondary development explains why ABCs can sometimes be found alongside other bone abnormalities.
Trauma or injury to the bone has also been proposed as a possible trigger. A bone injury might cause bleeding inside the bone and disrupt normal bone remodeling, creating an environment where an aneurysmal bone cyst can form. However, trauma is not a consistent factor in all cases, and many ABCs occur without any known injury.
ABCs most commonly affect children and adolescents, typically occurring in the metaphysis (the growing end) of long bones such as the femur, tibia, or humerus, as well as in the spine. The cysts can cause symptoms like pain, swelling, and sometimes pathological fractures due to weakening of the bone structure.
In summary, aneurysmal bone cysts result from a combination of abnormal blood vessel proliferation, genetic mutations (especially involving the USP6 gene), and sometimes secondary changes related to other bone lesions or trauma. These factors lead to the formation of blood-filled cystic spaces that expand and damage the bone, causing the clinical features associated with ABCs.
