Bone cysts

Bone cysts are fluid-filled bone lesions that can occur in any bone in the body but are most commonly found in the long bones of the arms and legs, particularly in children and adolescents. They are generally benign (non-cancerous) and can be classified into two main types: unicameral (simple) bone cysts and aneurysmal bone cysts.

Types of Bone Cysts

Unicameral Bone Cysts

Unicameral bone cysts (UBC), also known as simple bone cysts, are the most common type of bone cyst. They typically occur in the long bones, such as the femur (thigh bone) or humerus (upper arm bone), near the growth plate. These cysts are filled with clear fluid and are often discovered incidentally during imaging for another condition or after a pathologic fracture occurs through the cyst.

Aneurysmal Bone Cysts

Aneurysmal bone cysts (ABC) are less common and more aggressive than unicameral bone cysts. They can expand rapidly and cause significant bone destruction. ABCs are characterized by several blood-filled, septated spaces within the bone. They can occur in any bone in the body but are most frequently found in the spine, pelvis, and long bones. The cause of aneurysmal bone cysts is not fully understood, but they may arise de novo or secondary to another lesion.

Symptoms

Many bone cysts are asymptomatic and are discovered incidentally during imaging studies for unrelated reasons. When symptoms do occur, they may include:

• Pain, which can be caused by a pathological fracture through the cyst
• Swelling or a visible lump
• Restricted movement if the cyst is near a joint

Diagnosis

Diagnosis of bone cysts typically involves a combination of clinical evaluation and imaging studies. X-rays are usually the first step and can reveal the cyst's location, size, and effect on the surrounding bone. Magnetic resonance imaging (MRI) or computed tomography (CT) scans may be used to further evaluate the cyst's characteristics and its relationship to surrounding structures.

Treatment

The treatment of bone cysts depends on several factors, including the type of cyst, its location, size, and whether it is causing symptoms. Options may include:

• Observation, for asymptomatic cysts that are not at risk of causing fractures
• Aspiration and injection of steroids or bone marrow, which can help reduce the size of the cyst and stimulate bone healing
• Surgical curettage and bone grafting, to remove the cyst and fill the cavity with bone graft material
• In cases of aneurysmal bone cysts, more aggressive surgical intervention may be necessary to remove the cyst and stabilize the affected bone

Prognosis

The prognosis for individuals with bone cysts is generally good, especially for those with unicameral bone cysts. Many cysts heal with treatment, though there is a risk of recurrence, particularly in younger patients whose bones are still growing. Aneurysmal bone cysts have a higher recurrence rate and may require more aggressive treatment.

See Also

• Bone tumor
• Osteosarcoma
• Ewing's sarcoma
• Pathologic fracture