On this page
- What Is a Bone Cyst?
- When Is Removal Necessary?
- How Is a Bone Cyst Treated?
- How Long Does Recovery Take After Surgery?
- Can a Removed Cyst Come Back?
- Why Do Bone Cysts Form?
- Symptoms of Bone Cysts
- Dangers and Possible Complications
- When to Contact Your Doctor or Pediatrician
- Diagnosis
- Frequently Asked Questions
- Sources and Bibliography
What Is a Bone Cyst?
A bone cyst is a fluid-filled sac that develops within a bone. Bone cysts primarily affect children and adolescents, and in the vast majority of cases they are not dangerous, often tending to improve or even resolve completely on their own over time as the child grows.
In many cases, a doctor may simply recommend periodic monitoring through follow-up X-rays to track how the cyst is evolving over time. Surgical removal is only rarely necessary and is generally reserved for specific situations where the cyst poses a meaningful risk to the affected bone’s strength or function.
It is important for parents and patients to understand that a diagnosis of a bone cyst, while understandably concerning to hear, is generally not a cause for alarm. These are benign, non-cancerous formations that behave very differently from bone tumors, and the overall outlook for children diagnosed with a bone cyst is excellent.
When Is Removal Necessary?
Doctors generally consider surgical intervention when the cyst progressively increases in size, and as a result begins to cause:
- weakness or fragility of the affected bone, making it more susceptible to fracture,
- excessive pain and/or swelling that affects the child’s daily activities, comfort, or quality of life.
The decision to proceed with surgery is always individualized, taking into account the size and location of the cyst, the age of the patient, the specific type of cyst involved, and whether there has already been a fracture or significant symptoms.
How Is a Bone Cyst Treated?
The only definitive treatment strategy available for bone cysts that require intervention is a surgical approach, though there are actually two distinct surgical techniques that can be used depending on the specific characteristics of the cyst and the clinical judgment of the treating orthopedic surgeon:
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Needle drainage (aspiration) of the fluid contained within the cyst. This minimally invasive approach also allows for the direct injection of medications into the cyst cavity that can help promote proper bone healing. It is worth noting that this approach may need to be repeated over the course of several months, as a single treatment session does not always achieve complete resolution.
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Surgical removal (curettage) of the cyst, which often requires filling the resulting cavity with small pieces of bone. This bone graft material can be taken from another part of the patient’s own body (an autograft), obtained from a donor (an allograft), or, alternatively, artificial bone graft substitutes can be used to fill the space and support new bone growth.
Both surgical approaches are typically performed under general anesthesia and, in most cases, do not require an overnight hospital stay, being conducted instead on a day-surgery (outpatient) basis, allowing the child to return home the same day.
How Long Does Recovery Take After Surgery?
Recovery following surgical treatment of a bone cyst generally requires a period of several months, during which the patient will need to refrain from sports activities and other strenuous physical exertion to allow the bone to properly heal and regain its normal strength. Your surgeon will provide specific guidance on when it is safe to gradually return to physical activity based on follow-up imaging showing adequate bone healing.
It is strongly recommended to promptly report any new swelling that develops after surgery to your treating physician, as this could potentially be a sign of either a recurrence (meaning a new cyst has formed in the same location) or, less commonly, a postoperative infection, both of which would require further evaluation and management.
Can a Removed Cyst Come Back?
Unfortunately, yes. Recurrence of a bone cyst following surgical treatment is possible, and this risk is particularly notable during the first two years following the initial procedure. As a general rule, the younger the patient is at the time of surgery, the greater the likelihood that the cyst may eventually return. This is thought to be related to the fact that younger children have more remaining bone growth ahead of them, providing more opportunity for the underlying process that originally created the cyst to recur.
Despite this possibility, it is important to note that recurrent cysts can generally be managed successfully with repeat treatment, and long-term outcomes for children who experience recurrence remain very good overall.
Why Do Bone Cysts Form?
The exact underlying cause of bone cysts remains unknown. However, it is very important to clearly emphasize that bone cysts are NOT tumors, and precisely because of this fundamental distinction, bone cysts are not capable of spreading to other parts of the body, unlike malignant bone tumors.
When examining their internal composition and characteristics, bone cysts can be classified into two main distinct types:
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Unicameral (simple) bone cyst: This is a single-chambered, fluid-filled lesion that tends to form during a child’s growth phase, when proper drainage of fluid within the bone is not possible, likely due to localized disturbances in blood circulation within the developing bone. This represents the most common form of bone cyst and is diagnosed more frequently in boys than in girls.
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Aneurysmal bone cyst: This type consists of a blood-filled formation, the exact cause of which remains unclear, though it is believed to potentially represent the bone’s abnormal response to some form of local injury or insult. Aneurysmal bone cysts are occasionally associated with other underlying bone lesions, including giant cell tumor of bone or osteoblastoma, both of which are distinct bone conditions that a doctor will want to rule out or identify during the diagnostic workup.
Closely related to bone cysts, though a distinct entity in its own right, is the non-ossifying fibroma, which represents the most common benign bone lesion overall (it is important to clarify that this is emphatically NOT bone cancer). This condition is extremely common in children between the ages of 2 and 18, with estimates suggesting that as many as one in three children under the age of 20 may have one at some point, even if it is never discovered or causes any symptoms. Non-ossifying fibromas are typically completely asymptomatic, and their exact cause similarly remains unknown. When particularly small in size, this condition is sometimes referred to instead as a “fibrous cortical defect”.
Symptoms of Bone Cysts
In the majority of cases, a bone cyst causes absolutely no symptoms whatsoever and is discovered purely incidentally, often during a medical examination or imaging test performed for a completely unrelated reason, such as an X-ray taken after a minor injury. Less commonly, a patient (or, in the case of young children, a parent) may notice a small, painless bump or protuberance on the affected bone.
Although bone cysts can technically develop in any bone of the body, unicameral bone cysts most typically affect the long bones of the body, particularly the upper arm bone (humerus) or the thigh bone (femur). They are generally observed affecting only a single bone at a time, typically located near one end of the bone, close to the joint and the growth plate, the area of the bone responsible for its lengthening during childhood and adolescence.
As the affected bone continues to grow throughout childhood, the shape and size of the cyst can change correspondingly. Importantly, these cysts generally stop growing once the individual reaches adulthood, at which point the fluid-filled cavity will typically and gradually fill in with normal, healthy bone tissue over time, until it eventually disappears entirely.
Aneurysmal bone cysts, in contrast, more frequently cause noticeable pain and visible external swelling of the affected area, making them somewhat more likely to come to medical attention due to symptoms rather than being discovered incidentally.
Dangers and Possible Complications
The primary concern associated with bone cysts, particularly larger ones, is that the affected bone can become excessively fragile as a result of the cyst weakening its normal structure. This increased fragility places the bone at risk of fracture, even following relatively minor trauma that would not normally be expected to break a healthy bone. This type of fracture, occurring through an area of bone weakened by an underlying condition such as a cyst, is medically termed a pathologic fracture.
Interestingly, it is worth noting that in approximately 25 percent of cases, the bone cyst actually heals completely and permanently as a direct result of the healing process that occurs following such a fracture, meaning the fracture itself can sometimes serve as an unexpected form of natural “treatment” for the underlying cyst. In the remaining cases, however, surgical intervention may be recommended specifically to strengthen the affected bone and prevent the occurrence of a future fracture.
When to Contact Your Doctor or Pediatrician
It bears repeating that the vast majority of bone cysts are entirely harmless and require no specific treatment beyond periodic monitoring. That said, it is important to promptly report any new or unexplained swelling to your treating physician, allowing for proper evaluation and accurate diagnosis.
If your child has already received a diagnosis of a known bone cyst, it is recommended to contact your doctor again promptly if you notice that the swelling appears to be increasing in size, as this may warrant a re-evaluation and potentially a change in the recommended management approach.
Diagnosis
Confirmation of the diagnosis of a bone cyst is generally achieved through a standard X-ray examination, which in many cases is sufficient on its own to identify the characteristic appearance of a bone cyst and distinguish it from other bone conditions.
In some cases, additional imaging studies may be requested, such as a CT scan or MRI (magnetic resonance imaging), particularly to help distinguish between the different types of bone cysts, since unicameral and aneurysmal bone cysts may ultimately require somewhat different treatment approaches based on their specific characteristics and behavior.
Only in rare cases, typically when there is diagnostic uncertainty or concern about an alternative underlying condition, is a biopsy (the surgical removal of a small tissue sample for laboratory examination) ultimately required to confirm the diagnosis with complete certainty.
Frequently Asked Questions
Are bone cysts a form of cancer?
No. Bone cysts are entirely benign, fluid-filled formations and are fundamentally different from bone tumors or cancer. They do not spread to other parts of the body and, in most cases, do not pose any serious long-term health risk.
At what age do bone cysts typically develop?
Bone cysts most commonly develop during childhood and adolescence, generally in individuals still undergoing active bone growth. They are relatively uncommon in adults, and when they do occur, this is typically because a cyst originally formed during childhood was never diagnosed or treated.
Can a bone cyst heal without any treatment at all?
Yes, many bone cysts, particularly smaller unicameral cysts, resolve spontaneously over time as the child grows, without requiring any specific medical or surgical intervention. Regular monitoring through periodic X-rays is often all that is needed in these cases.
Is surgery for a bone cyst considered a major operation?
Generally, no. Most surgical procedures used to treat bone cysts, including both needle aspiration and surgical curettage with bone grafting, are performed on an outpatient (day-surgery) basis under general anesthesia, and most children are able to return home the very same day.
Can bone cysts cause long-term problems with bone growth?
In most cases, no. Bone cysts located near a growth plate are generally monitored carefully specifically because of their proximity to this important area of bone growth, but with appropriate management, long-term growth disturbances are uncommon. Your child’s orthopedic specialist will monitor growth closely if the cyst is located near a growth plate.
Sources and Bibliography
- American Academy of Orthopaedic Surgeons (AAOS). Unicameral Bone Cysts
- Johns Hopkins Medicine. Bone Cysts
- StatPearls. Bone Cyst
