Aneurysmal Bone cyst

What is an aneurysmal bone cyst?

An aneurysmal bone cyst (ABC) is a benign but locally aggressive lesion of bone. Despite the word aneurysmal, it is not a true aneurysm (an expanded blood vessel). It consists of blood-filled spaces separated by bony septa (walls), lined by fibrous tissue containing giant cells. ABCs can expand rapidly, weaken the bone significantly, and — unlike simple bone cysts — can be locally destructive.

Is it cancerous? 

NO

Where do ABCs occur?

ABCs can arise in virtually any bone. Common sites include the long bones (femur, tibia, humerus), the spine, and the pelvis. They most often arise in the metaphysis (the growing end of the long bone) and can extend significantly. They occur most commonly in children, adolescents, and young adults.

Symptoms

• Pain — often worse at night

• Swelling over the affected bone

• Pathological fracture in some cases — fracture through the weakened bone

• If in the spine: back or neck pain, rarely neurological symptoms

Treatment options

ABCs can be treated with several different approaches. The best treatment depends on the size of the lesion, its location, how aggressive it appears on imaging, and whether it has been biopsied. Treatment decisions are made by a specialist multidisciplinary team.

1. Observation

Rarely appropriate for ABCs due to their tendency to grow rapidly. Occasionally used for very small, incidentally found, and asymptomatic lesions that are being monitored closely.

2. Curettage and bone grafting

Intralesional curettage is the traditional surgical approach. The lesion is opened through a cortical window, the blood-filled cavities are emptied, and the walls are thoroughly curetted. Adjuvants such as phenol, liquid nitrogen, or burring with a high-speed drill are sometimes applied to the cavity walls to reduce recurrence risk. The cavity is then packed with bone graft (autograft, allograft, or synthetic substitute) or calcium phosphate cement.

• Most widely used treatment

• Recurrence rate: approximately 10-30% (higher in younger children and larger lesions)

• May require repeat surgery if recurrence occurs

3. Selective arterial embolisation

Embolisation is a minimally invasive procedure performed by an interventional radiologist. Under X-ray guidance, a catheter is passed through the blood vessels (usually via the femoral artery at the groin) to the blood vessels supplying the ABC. Small particles or coils are injected to block the blood supply to the lesion. This causes the ABC to shrink and resolve over time.

• No incision at the bone — minimally invasive

• Often performed as a series of 2-4 sessions, 4-6 weeks apart

• Particularly useful for lesions in difficult locations (e.g. pelvis, spine, proximal femur)

• Can be used as a primary treatment or to reduce vascularity before surgical curettage

• Success rate: approximately 70-90% after a course of embolisations

• Risks: skin or soft tissue damage from embolisation particles, temporary pain flare after procedure

4. Sclerotherapy

Sclerotherapy involves injecting a sclerosing agent — most commonly Polydocanol or doxycycline — directly into the ABC under imaging guidance. The sclerosant destroys the lining of the blood-filled cavities, causing them to fibrose (scar) and the cyst to resolve.

• Performed percutaneously (through the skin) under X-ray or CT guidance

• Multiple sessions are typically required — usually 3-6

• Best suited to accessible, well-defined lesions

• Avoids open surgery

• Success rate comparable to curettage in selected cases

• Risks: leakage of sclerosant into soft tissues, local pain, allergic reaction

5. Denosumab

Denosumab is a monoclonal antibody that blocks RANK ligand — a signalling molecule involved in bone resorption by giant cells. Given by subcutaneous injection, it can cause ABCs to calcify and become less aggressive. It is used in some specialist centres for large, recurrent, or surgically difficult ABCs.

• Not universally available — specialist centre decision

• Requires a course of injections

• May be used to stabilise the lesion before surgery

• Rebound growth after stopping denosumab has been reported — this remains an area of active research

Which treatment is recommended for your child?

Your surgical team will have reviewed your child’s imaging and biopsy at a specialist multidisciplinary team meeting. The recommended treatment will be discussed with you at your consultation and will be tailored to your child’s specific lesion.

Risks of surgical curettage (most common surgical approach)

• Wound infection

• Bleeding — ABCs are vascular and blood loss can be significant; pre-operative embolisation reduces this

• Pathological fracture during or after surgery

• Recurrence — 10-30%, higher in younger patients

• Injury to adjacent nerves or blood vessels

• Anaesthetic risks

Note: Reassurance — and important caveats 

An aneurysmal bone cyst is benign — it is not a cancer and does not spread to other parts of the body. However, ABCs can grow aggressively, cause significant bone destruction, and have a meaningful recurrence rate after treatment. It is important that an ABC is properly investigated to confirm the diagnosis before treatment, as some malignant bone tumours can look similar on imaging. Your child’s imaging and biopsy results will have been reviewed by a specialist multidisciplinary bone tumour team.

Note: When to seek urgent help 

Sudden severe pain or inability to bear weight — possible pathological fracture Numbness, weakness, or bowel/bladder changes if ABC is near the spine Wound infection: increasing redness, discharge, temperature above 38.5°C Rapid increase in size or pain of a known lesion

This information is for general guidance only and is not a substitute for a consultation with Mr Wadia. If you are worried about your child, please seek medical advice.