Bone cyst


Bone cyst


A bone cyst is a fluid-filled hole that develops inside a bone. They can occur at any age, but most often affect children and young adults.

Bone cysts don't usually cause any symptoms. They are not cancerous and they do not usually pose a serious threat to health.

However, large cysts can cause a bone to weaken, making it more likely to fracture (break). This can cause problems such as pain, swelling, or not being able to move or put weight on a body part.


Types of bone cysts

There are two main types of bone cysts.

Unicameral bone cysts

Unicameral bone cysts are the most common type of bone cyst. They can develop anywhere in the body, although most cases involve either the upper arm or thigh.

The condition tends to affect younger children between 5 and 15 years of age. Boys are about twice as likely to have unicameral bone cysts as girls.

The exact cause of unicameral bone cysts is unknown, but a leading theory suggests they may occur due to problems with the drainage of interstitial fluid from growing sections of bone.

Aneurysmal bone cysts

Aneurysmal bone cysts are a rarer type of bone cyst where the bone contains a pocket of blood. They can also develop anywhere in the body, but most often affect the legs, upper arms, pelvis or spine.

Most cases affect children and young people aged between 10 and 20. It's thought that aneurysmal bone cysts may be slightly more common in females than males.

The exact cause of aneurysmal bone cysts is not clear. They may occur because of an abnormality in the blood vessels inside affected bones, which develop as a result of a previous injury or a non-cancerous growth inside the bone.

Diagnosing bone cysts

Bone cysts can usually be diagnosed by looking at an X-ray of the affected bone. This will highlight any hollow cavities or fractures in the bone.

In many cases, a bone cyst will only be discovered by chance when X-rays are used to diagnose an unrelated condition, or after an affected bone has fractured.

A computerised tomography (CT) scan, a magnetic resonance imaging (MRI) scan, and/or a biopsy (where a sample of fluid is removed from the bone with a needle and tested) may sometimes be carried out to confirm the diagnosis.


How bone cysts are treated

Many bone cysts will eventually heal without the need for treatment and won't cause long-term problems – particularly unicameral bone cysts in children, which will usually disappear by the time they stop growing.

If a bone cyst does not get better, or if treatment is recommended to help reduce the risk of a fracture, several options may be available.

For example, steroid medication can be injected into the bone to encourage the cyst to heal. If this doesn't help, surgery may be needed to drain the fluid and fill the hole with chips of bone.

There is a significant chance of the cyst recurring after treatment, so you may need to have regular X-rays for a few years afterwards to look for signs of the condition returning.


Bone cysts are usually picked up during an X-ray 


Bone is a hard, dense tissue that shows up clearly on X-rays, making them very useful for diagnosing bone-related problems


Symptoms of bone cysts 

Bone cysts often have no symptoms. They may not be discovered until you fracture (break) the bone, or until you have an X-ray for another reason.

Unicameral bone cysts

Most unicameral bone cysts do not cause any symptoms unless the affected bone becomes severely weakened, causing it to fracture.

Signs and symptoms of a fracture can include:

pain and swelling

bruising or discoloured skin around the bone or joint

the limb or affected body part being bent at an unusual angle

inability to move or put weight on the injured limb or body part

In most cases, the bones of the upper arms or legs are affected.

Occasionally, unicameral bone cysts may cause pain without any obvious signs of a fracture, and they may disrupt the growth of the affected bone.


Aneurysmal bone cysts

Signs and symptoms of an aneurysmal bone cyst can include:

persistent pain and swelling

a noticeable lump or deformity in the bone

decreased range of movement, weakness or stiffness in the affected body part

the skin in the affected area being warm to the touch

Most aneurysmal bone cysts affect bones in the legs, upper arms, pelvis or spine.

If an aneurysmal bone cyst develops inside the spine, it can disrupt the normal working of the nervous system and cause additional symptoms, such as:

muscle weakness

a shooting pain in the arms or legs (sciatica)

numbness or a tingling sensation in the arms and legs

problems with bladder or bowel control

Although it happens less often than in unicameral bone cysts, aneurysmal bone cysts can also sometimes cause fractures in affected bones.


When to seek medical advice

You should contact your GP if you or your child experiences persistent bone pain or any of the signs of a problems described above.

If you think that you or your child has a fracture, go to your nearest accident and emergency (A&E) department. Dial 999 for an ambulance if the injury is severe.


Treating bone cysts 

Many bone cysts will eventually heal without treatment and won't cause any permanent problems.

This is particularly true of unicameral bone cysts in children, which will usually disappear around the time they finish growing.

However, treatment is sometimes necessary if the cyst is painful or is at risk of causing a fracture.

If a cyst has already caused a fracture, this will need to be dealt with before the cyst is treated – usually with painkillers, rest and a plaster cast.


Unicameral bone cysts

If the cyst is small and the affected bone is strong, you or your child may not receive any immediate treatment, but will be given regular check-ups to make sure the cyst is not getting bigger.

Surgical treatment may be recommended if the cyst does not show any signs of healing or if the bone is thought to have a high risk of fracture. There are three main types of surgical treatment:

steroid injections – where fluid is drained out of the cyst before steroid medication is injected into it; several injections may be required a few months apart to help ensure the cyst fully heals

bone marrow injections – similar to steroid injections, but the surgeon injects bone marrow that has been removed from another part of the body to encourage the cyst to heal

curettage and bone grafting – where the surgeon cuts into the bone, drains the cyst, and scrapes out the lining of the cyst; the resulting hole is then usually filled with chips of bone from another part of the body or a donor

All three techniques are carried out under general anaesthetic, which means that you or your child will be asleep during the surgery and will not feel any pain. Most people can go home later the same day, although you may need to take things easy for a few months while you recover.

In some cases, unicameral bone cysts can return after treatment, usually within a year or two. Therefore, it's likely that you or your child will have regular X-rays to assess the condition of the affected bone and check for signs of the cyst recurring.


Aneurysmal bone cysts

Aneurysmal bone cysts usually need to be treated because they don't tend to get better on their own and they can get bigger rapidly. In many cases, simple treatment such as carrying out a biopsy of the cyst will start the healing process.

If this does not work, they are treated using curettage and sometimes with bone grafting, as described above.

In some cases, additional treatments such as a procedure to block the blood supply to the blood vessels near the cyst (embolisation) or to freeze and damage the tissue of the cyst using liquid nitrogen may also be carried out.

Like unicameral bone cysts, aneurysmal bone cysts may sometimes come back after treatment. This usually happens within 18 months, if it’s going to.