Unicameral Bone Cyst

What is an unicameral bone cyst?

A unicameral bone cyst (UBC) is a benign (non-cancerous), fluid-filled cavity in the bone, which does not spread. It usually affects children between ages 5-15, but can also affect older children.

Typically UBCs appear in the bones of the upper arm (near the shoulder) or leg (near the hip), but other bones can be affected. For example, in older children the UBC can occur in the pelvis, jaw, rib cage, skull or heel bone.

Active unicameral bone cysts tend to grow larger and are located near the growth plates — the soft parts of the ends of bones which determine how tall a person will grow — and rarely have long-term effects on bone length. Inactive UBCs are generally located further away from growth plates and heal completely after treatment.

Unicameral bone cysts can cause the bone to be weak, and is most often diagnosed when a fracture occurs. At times, UBCs can prevent a limb from growing properly if they involve the growth plate.

In rare cases, UBCs can cause limb length discrepancies, meaning, for example, one leg would be shorter than the other. While leg function would not be impaired, the difference in length can cause gait issues.

UBCs may heal spontaneously by the time the child reaches skeletal maturity.

Causes

It is not known what causes unicameral bone cysts.

Signs and symptoms

Most children with a unicameral bone cyst will experience no symptoms. In most cases, unicameral bone cysts are only discovered when the child breaks the bone that has been weakened by the bone cyst.

Testing and diagnosis

At Children’s Hospital of Philadelphia (CHOP), your child's diagnostic evaluation begins with a thorough medical history and physical examination of your child.

Clinical experts may use a variety of diagnostic tests to diagnose unicameral bone cysts, including:

  • X-rays, which produce images of bones on film.  Usually this is the only test needed to diagnose a UBC.
  • Magnetic resonance imaging (MRI), which uses a combination of large magnets, radiofrequencies and a computer to produce detailed images of organs, soft tissues, muscles, ligaments and other structures within the body. Your child is exposed to no radiation during an MRI.
  • EOS imaging, an imaging technology which creates 3-dimensional models from two flat images. Unlike a CT scan, EOS images are taken while the child is in an upright or standing position, enabling improved diagnosis due to weight-bearing positioning.
  • Needle biopsy, a procedure where a doctor places a small needle through the skin and into the lesion to withdraw a sample of the abnormal tissue. The tissue is analyzed to confirm any findings.

In addition to diagnosing the specific type of lesion your child may have, these tests will also help determine the size and location of the cyst. All of this information is crucial in determining the best treatment options for your child.

Treatments

There are many treatment options available for unicameral bone cysts, and some children will need a combination of these therapies. At CHOP, experts at the Bone and Soft Tissue Tumor Program take a team approach to treatment. Orthopaedic and other specialists collaborate to provide your child with individualized care and the best possible outcomes.

Our program is led by Kristy L. Weber, MD, and Alexandre Arkader, MD, nationally renowned surgeons who specialize in treating bone and soft tissues tumors, limb-sparing surgery and reconstructive surgery.

Treatment for unicameral bone cysts depends on a number of factors including where the cyst is located, how strong the bone is where the cyst is located and what are the chances of a bone fracture.

In some cases, your child’s physician may recommend “watchful waiting” — regular monitoring. Some unicameral bone cysts will heal spontaneously. In more severe cases — such as when a bone is weakened at the location of the cyst — active treatment may be recommended. 

At Children’s Hospital of Philadelphia, we use one or a combination of the following surgical procedures.

Intralesional curettage and bone grafting

This procedure is generally done for UBCs that occur near the hip.  Curettage involves aspirating (draining) the fluid from the cyst, scraping out the bone to completely remove the tumor and all cyst lining. The area that was removed will be then packed with artificial graft material or cadaver bone.  It is possible that a metal plate would need to be inserted to stabilize the bone to prevent a fracture. This can all be done through a minimally invasive procedure.

Steroid injection

Injecting a steroid mixture into a unicameral bone cyst can sometimes heal the cyst without any other therapy. It’s not fully understood why the steroid heals the cyst, but doctors believe the steroids help the cyst to be reabsorbed into the bone.  This procedure is generally done for UBCs that occur near the shoulder.

For this procedure, doctors use biopsy needles to aspirate (drain) the fluid from the cyst, then inject the steroid into the same area. Over the following 12 to 20 months, your child will return for X-rays to determine if the UBC is filling in with normal bone.  If not, additional steroid injections may be necessary until there is full healing.

Because injections and curettage have similar results — and the impact on children is so different — our doctors prefer to use injections when possible.

Your child’s clinical team will recommend the best treatment for your child’s individual situation.

Surgical safety

Though surgery for tumors is highly effective, we understand that any surgery can be a stressful experience for children and families. At CHOP, we offer a wealth of resources about how to prepare your child for surgery and what to expect during surgery.

Additionally, we employ numerous best practices before, during and after surgery to decrease the risk of infection and increase positive outcomes. For more details about safety protocols at Children's Hospital of Philadelphia, see safety in surgery.

Follow-up care

At Children's Hospital of Philadelphia, we offer ongoing support and services for patients and families at our Main Campus and throughout our CHOP Care Network. Our team is committed to partnering with parents and referring physicians to provide the most current, comprehensive and specialized care possible for your child.

Unicameral bone cyst tumors recur in up to 50 percent of cases — even after treatment — so it is important for your child to continue to see a doctor after treatment.

Your child will see the orthopaedic surgeon about one to two weeks after surgery, then again every three to four months for two years to monitor for possible recurrence of the growth.

During follow-up visits, X-rays and other diagnostic testing of the tumor site are recommended to closely monitor your child’s health, check the reconstruction, and make sure there is no recurrence.

If the unicameral bone cyst returns, surgeons will treat the recurrence with steroid injections or intralesional curettage and bone grafting.

In most cases, unicameral bone cysts will not recur after your child has reached skeletal maturity.

Outlook

The health outlook for children with unicameral bone cysts is good. Most of these benign bone cysts will be treated successfully or will heal on their own by the time your child stops growing.

Providers Who Treat Unicameral Bone Cyst

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