Unicameral Bone Cyst

What is a unicameral bone cyst?

Unicameral bone cysts, also known as simple or solitary bone cysts, are benign (noncancerous) bone tumors. They occur most often in children and adolescents under 20. Unicameral bone cysts are fluid-filled spaces inside your bone. The word unicameral means “one chamber” and describes the single fluid-filled chamber in each cyst.

Unicameral bone cysts can grow in any bone. Most form in the long bones of your upper arms near your shoulders, and in your legs near your hips. Usually, unicameral bone cysts are painless and found by chance on an X-ray taken for another reason. Pain and swelling can occur if the bone around the cyst fractures.

What are the types of unicameral bone cysts?

Unicameral bone cysts develop near growth plates, which are the areas of active growth near the ends of bones. As your child’s bone grows, the cysts tend to move away from their growth plate.

The two types of unicameral bone cysts are:

• Active cysts are next to the growth plate and may expand over time. As the cyst expands, the bone around it can weaken and fracture.
• Latent cysts are located away from the growth plate and are no longer growing. As your child reaches maturity and bone growth stops, most cysts will fill in with bone and disappear.

How common are unicameral bone cysts?

Unicameral bone cysts are a relatively common type of bone tumor, more likely to occur in people designated male at birth than people designated female at birth. Their actual occurrence is unknown because many people with unicameral bone cysts have no symptoms and are never diagnosed.

What causes unicameral bone cysts?

Healthcare providers aren’t sure what causes unicameral bone cysts. A defect in the bone or a blockage in a vein may cause fluid to build up and cysts to form.

What are the symptoms of unicameral bone cysts?

Most children with unicameral bone cysts are asymptomatic or have mild symptoms close to where the cyst is located, such as:

• Slight pain.
• Swelling.
• Tenderness.

If the cyst causes the bone to fracture, symptoms include:

• Bruising.
• Difficulty moving.
• Pain.
• Swelling.
• A visible change in shape or alignment of the bone.

How are unicameral bone cysts diagnosed?

An X-ray is the main tool healthcare providers use to diagnose a unicameral bone cyst as they typically show good contrast between the bone and the cyst.

Your child’s provider may recommend additional testing including:

• MRI to evaluate the inner cavity of the cyst.
• CT scan, which is especially useful to examine cysts in areas that are difficult to assess using X-rays, such as the spine or pelvis.
• Biopsy to remove a small tissue sample. A pathologist, who specializes in diagnosing diseases, uses a microscope to examine the tissue for abnormalities.

These tests can help your child’s provider distinguish a unicameral bone cyst from other conditions or pathologies, such as an aneurysmal bone cyst or fibrous dysplasia.

What factors determine unicameral bone cyst treatment?

Your child’s treatment will depend on many factors, including:

• The size of the cyst.
• Strength of the bone.
• Their symptoms.
• Their age and activity level.

For small cysts that don't cause symptoms, your child’s provider may monitor the cyst with routine X-rays. Your child may also need to limit certain types of physical activity to reduce their risk of fracture.

If the cyst is large, causes your child symptoms or the bone is at risk of fracturing, your child’s provider may recommend treatment.

How are unicameral bone cysts treated?

Minimally invasive treatment with injections can be effective in helping cysts heal. Your child’s provider numbs the area and uses a needle to remove fluid from the cyst. The provider then injects methylprednisolone, a steroid, into the cavity. This may require a series of injections.

Sometimes, a surgical procedure called curettage is the best treatment option. A surgeon opens the cyst and scrapes out its contents and lining. The surgeon may apply a substance, such as ethanol, to the inside of the cavity to destroy any remaining cyst cells.

Afterward, the surgeon may use a bone graft (a piece of bone taken from another part of your body or from donated bone) or cement to fill the cavity.

How long is recovery after surgery?

After surgery, your child’s provider will immobilize the affected bone with a cast or sling while it heals. Most children resume their normal activities within three to six months after surgery. Your child’s provider will guide you throughout your child’s recovery. Follow-up care may include physical or occupational therapy to help your child gradually return to full activity.

What if the bone fractures?

Treatment for a fracture usually involves a cast to immobilize the bone and allow it to heal. If the fracture involves the growth plate, your child may need additional treatment depending on the severity. Treatments for growth plate fractures may include:

• Casting.
• Setting the bone.
• Surgery, possibly with metal screws, pins or plates.

Some cysts (1 in 4) will heal on their own after a fracture. If the cyst does not heal, your child’s provider may recommend surgery to remove the cyst and prevent another fracture.

Can unicameral bone cysts return after treatment?

Unicameral bone cysts return (recur) after treatment in up to 50% of children (1 in 2). Recurrence is more likely in very young children. Your child’s provider will schedule routine follow-up visits and X-rays to monitor your child for any recurrent cysts.

How can I prevent unicameral bone cysts?

There is no way to prevent unicameral bone cysts because providers aren’t sure why they occur.

What is the prognosis for children and adolescents with unicameral bone cysts?

Most unicameral bone cysts don’t cause symptoms and resolve on their own when a child is fully grown.

If a child has symptoms, has had a fracture or is at risk of a fracture, effective treatments are available. Ongoing monitoring is important as cysts frequently recur after treatment, especially in very young children.

Rarely, a fracture or surgical procedure may cause the bone to stop growing. If this happens, your child’s healthcare provider will offer care and resources for you and your child.

When should I contact my healthcare provider?

Call your provider if your child complains of pain near a bone or if you notice any swelling. Early detection of a unicameral bone cyst can prevent possible fractures and bone abnormalities.

A note from Cleveland Clinic

Unicameral bone cysts are usually found in children and adolescents. Most children with unicameral bone cysts don't have any symptoms. If your child has mild pain, tenderness or swelling near a bone, talk to their healthcare provider. Observation may be all that's needed. If the bone is at risk for fracture, their provider will recommend treatment followed by close monitoring because cysts often return. Once your child stops growing, the cysts usually go away on their own.