Bone Cysts – All You Need to Know

Overview:

Bone cysts are fluid-filled or blood-filled areas inside growing bone tissue. While they are not usually very serious, treatment is nevertheless required. The blog explains the two main types of bone cysts along with their treatment options.

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Bone cysts are fluid-filled regions that develop inside growing bone tissue. They are usually nothing to be worried about but in some cases, surgical intervention may be required. Children and adolescents are more susceptible to bone cysts.

In this blog, we will take a look at the two most common types of bone cysts – unicameral and aneurysmal.

Unicameral Bone Cyst

Also known as a simple bone cyst, the unicameral cyst is a non-cancerous tumor that affects children and teenagers. Simply put, they are fluid-filled cavities that are located in bones.

While they can form in any bone, the long bones of the body like the thigh and upper arm bone are where they are usually detected. Most of the time these cysts do not cause any discomfort to the patient but they can affect the surrounding bone and weaken it and hence make the bone susceptible to fractures.

Treatment modalities depend on the size, location and fracture probability. Unicameral cysts are more common in boys than girls and they do not spread to other parts of the body. Once the child’s growth stops, the cysts will become normal bone tissue.

Unicameral cysts can be classified further depending on their location:

Active:

• These cysts are located bordering the growth plate.
• The growth plate is a cartilaginous tissue found at the end of bones which determines how long the bone will grow.
• When the cyst is touching the growth plate, it can increase in size and cause fracture. Further, it can even injure the growth plate resulting in bone deformation and unequal limb lengths.

Latent:

• Here, the cyst location is away from the growth plate.

Cause:

• The reason for the growth of these cysts is unclear.
• A growth plate disorder might be a possible cause.

Symptoms:

• These cysts are mostly symptomless and there will be no pain. Therefore, their detection is incidental when an x-ray is done for some other condition.
• Sometimes, a fracture will lead to the cyst discovery.
• When the bone strength is diminished by the cyst, even a small injury might lead to a fracture. Such a fracture is called a pathologic fracture.

Diagnosis:

• An x-ray can diagnose a unicameral bone cyst.
• Sometimes, an MRI or CT scan might be needed to differentiate between a unicameral and an aneurysmal bone cyst.
• If differentiation is still difficult, a biopsy of the fluid in the cyst will reveal the type of cyst.

Treatment:

• The treatment is dependent on a number of factors – size and location of the cyst, whether any pain is felt, bone strength and how active the child is.
• Small, painless cysts are usually just observed and no treatment is necessary.
• If the cyst is large and fracture risk is a concern, surgery may be considered.
• If the child presents after a fracture has happened, the fracture will usually self-heal and the cyst too might heal with the fracture.
• If the cyst does not heal, surgery to remove the cyst will be considered to reduce future fracture risk.

With unicameral cysts, the possibility of recurrence is 25-50%. Hence, regular follow-up will be necessary. Once the child becomes an adult, recurrence will stop and the cysts will become part of the bone.

Aneurysmal Bone Cyst

These cysts are benign bone tumors which affect children more than adults with girls being afflicted with it more than boys. Overall, their occurrence is rare with only 1 in 10000 being affected by it.

An aneurysmal bone cyst has many blood-filled sacs in it. While it can form anywhere, most of the time it is found close to the growth plate. These cysts can deform the bone and make it prone to fractures. A common location for these cysts is in the bones of the thigh, shin, shoulder and spine.

Cause

• The cause for formation is not known.
• However, it is observed that they can form in response to another benign bone tumor. A cyst thus formed is known as a secondary aneurysmal bone cyst.

Symptoms

• Patient will complain of pain and swelling, both of which aggravate with time.
• The pain will not have any obvious trigger (like injury).
• Reduced range of motion and decreased flexibility are other symptoms.
• In some cases, a fracture happens and the cyst is discovered after that.
• If the cyst is located in the spine, back pain or neck pain may be present.
• The patient may also complain of radiating nerve pain.
• Some cases can also be symptomless with the cyst being discovered during investigations for other reasons.

Diagnosis

• The doctor will ask about the patient’s medical history and will examine the painful/inflamed area.
• Typically, an x-ray will be needed for diagnosis. In some cases, an MRI or CT scan may be required.
• Blood tests are not usually advised.
• However, a biopsy may be needed for confirming diagnosis. During biopsy, a needle is used to get a small sample of the bone. If a bigger sample is needed, the procedure will be done in the operating room.

Treatment

• Surgical removal of the cyst is recommended.
• The surgeon will remove the tumor cells while taking care not to damage the growth plate or the healthy cells.
• After removing the cyst, the area will be filled with a bone graft (from a donor or from the patient himself) or a bone graft substitute.
• The bone may need to be supported with metal plates, screws, etc.
• After surgery, the area may be immobilized with a cast, brace, etc.
• If the bone is badly affected or the tumor keeps recurring, a wide resection will be done wherein the tumor cells are removed along with a margin of normal tissue.
• The procedure involves reconstructing the bone with donor tissue or a metal prosthetic.
• Other procedures like sclerotherapy and radiation therapy are reserved for tumors that are difficult to access, when surgery is not considered a safe option.

Recovery after surgery can take up to 6 months. Unfortunately, recurrence of these cysts is possible and hence follow-up visits with the doctor are important.