Aneurysmal Bone Cyst - Causes, Symptoms, Diagnosis, and Treatment

Introduction

An aneurysmal bone cyst is described as a benign (non-cancerous), and blood-filled lesion in the bone that manages to grow or expand. Although it is called a cyst, it is a true benign bone tumor surrounded by a thin wall of bone. Aneurysmal bone cysts (ABCs) may occur in any bone but are most typically found around the pelvis, knee, or spine.

What Is Aneurysmal Bone Cyst?

An aneurysmal bone cyst (ABC) is a benign destructive bone tumor that occurs most commonly in children or teenagers. It forms a cavity in the bone filled with fluids that tend to grow or enlarge. These cavities can weaken the bone, cause pain, swelling, and make it more prone to fracture. They are usually non-cancerous. About 70 percent of the aneurysmal bone cyst are the primary lesions in patients with no other diseases. But 30 percent of them appear in patients secondary to other bone lesions like hemangiomas (an unusual saturation of blood vessels in internal organs and the skin.), giant cell tumors (tumors which are benign and have the potential capacity to metastasize and may show aggressive behavior.), fibrous dysplasia (happens when abnormal fibrous (scar-like) tissue replaces healthy bone), and osteoblastoma (an uncommon benign bone-forming neoplasm).

What Causes Aneurysmal Bone Cyst in Adults?

• The cause of an aneurysmal bone cyst is not known, however, it can be because of the involved bone's blood vessels' disturbances.

• In another study, it was said that the aneurysmal bone cyst is due to the abnormalities in the chromosomes of the tumor cells, but these findings are unclear.

• It is not hereditary because none of the patient's family members are diagnosed with an aneurysmal bone cyst.

• The oncogenes are the tumor-causing cells that are activated by chromosomal translocation. These oncogenes can trigger destructive tumor tissue development, made up of giant cell osteoclast and vascular spaces.

• The oncogenes also trigger the matrix metalloproteinase, a protein that destroys and attacks the structural matrix of the bone and vascular endothelial growth factor in the body, which recruits more blood supply for the destructive tumor to make it grow rapidly.

What Can Be the Symptoms of Aneurysmal Bone Cyst?

The symptoms of an aneurysmal bone cyst might vary from patient to patient. The patient will realize that they have an aneurysmal bone cyst only when they have pain in the affected bone. In other patients, the involved bone will be fragile and thin, and the aneurysmal bone cyst will be discovered only when the bone fractures due to minimal trauma. The most common symptoms are given in the following.

• Pain.

• Swelling.

• Neurological symptoms.

• Fracture of the involved bone due to the cyst.

• Decreased range of motion, stiffness, or weakness.

• Felling warm in the affected area.

Each patient may get different symptoms, so it is necessary to take consultation with a physician so that the diagnosis can be made appropriately.

What Is the Epidemiology of the Aneurysmal Bone Cyst?

The aneurysmal bone cyst usually occurs in children and young adults, with about 80 percent of the cases diagnosed in patients less than 20 years of age.

What Is the Pathology Behind the Aneurysmal Bone Cyst?

Aneurysmal bone cyst consists of hollow spaces filled with blood and separated by the connective tissues and contains giant osteoclast cells and osteoid tissues. It is usually seen in the tubular bones in the feet, hands, and craniofacial bones. When it is seen in the long appendicular bones, it is known as a solid aneurysmal bone cyst.

What Is the Differential Diagnosis of an Aneurysmal Bone Cyst?

The differential diagnosis of an aneurysmal bone cyst may include:

• Chondroblastoma (a benign, chondroid-producing neoplasm composed of chondroblasts).

• Giant cell tumor of bone ( it is a type of benign (noncancerous) tumor that has a wide range of behaviors).

• Telangiectatic osteosarcoma (is typically a purely lytic lesion with a permeative destructive growth pattern).

• Fibrous dysplasia (happens when abnormal fibrous (scar-like) tissue replaces healthy bone).

How to Diagnose Aneurysmal Bone Cyst?

The diagnoses of an aneurysmal bone cyst may include:

• Physical examination.

• X-rays are done to determine the actual size of the cyst and any risk of fracture to the bone.

• MRI (magnetic resonance imaging) when done, can reveal the images of the cysts where it is located and the characteristics of the cysts.

• CT (computed tomography) is used to get a clear image of the bone lesion.

• The biopsy is done by collecting a tissue sample from the cyst to determine the type of cyst.

• An EOS imaging can be done. It is an imaging technology that can create a 3-dimensional model from two flat images. EOS images are taken when the patient is in an upright or standing position, facilitating improved diagnosis due to weight-bearing positioning.

• Angiography can also diagnose aneurysmal bone cysts. It is described as a radiograph-type X-ray test that reveals the inside of blood vessels and organs.

• A needle biopsy can be carried out for the diagnosis.

How to Treat Aneurysmal Bone Cyst?

• Medical history.

• Age of the child.

• The overall health of the child.

• The location of the cyst.

• Recurrence of the cyst.

• The risk of fracture of the bone.

The aneurysmal bone cyst can expand and alter the involved bone, and it may lead to pathological fracture and damage of the joints involved. They may cause pain and swelling and do not go away on their own. Surgery is required to avoid permanent damage to the bone. And before surgery, the surgeon may block the abnormal blood vessels present in the involved cysts through arterial embolization, which can reduce the excessive blood flow during the surgery. To know whether the child can undergo arterial embolization, the doctor may use an angiogram, a special X-ray used to visualize the blood vessel. The treatment can involve more than one or one of the following, done by a pediatric orthopedic surgeon.

1. Extended Curettage:

After the surgery, the additional layers of bone are removed with a special instrument in this procedure. It is the most aggressive type of procedure, but it is used to avoid further growth of cysts.

2. Curettage And Bone Grafting:

This is a surgery in which the cysts are scraped from the bone with a special instrument, and the remaining cavity is filled with the bone tissue from the donor (allograft) or from the bone chips of another bone (autograft).

3. Marginal Or Wide Excision:

This surgery involves removing part of the bone where the cyst is present, at its margin or beyond its margin, called wide excision. It is often performed in bones such as ribs and fibula. This procedure is avoided as much as possible because it could compromise the bone's function.

4. Cryotherapy:

Since the cysts can recur, in this procedure, the cysts are surgically frozen. It is sometimes done in addition to curettage and bone grafting, but it has complications like bone fracture, nerve injury, etc.

5. Sclerotherapy:

This is a non-surgical technique that is very helpful in healing the cyst. In this, the surgeon may inject a chemical inside the cyst to create scar tissue. This scar tissue may heal and harden inside the bone itself by avoiding open surgical methods.

Conclusion

The aneurysmal bone cyst can recur about 20 percent of the time; therefore, the doctor may call the patients for follow-up checkups for the first two years after the surgery to avoid recurrence. The recurrent aneurysmal bone cyst is treated with the same treatment option, but a more aggressive technique is avoided to prevent further recurrence.