Aneurysmal Bone Cyst (ABC)

Aneurysmal Bone Cyst (ABC)

Prepared by Dr. Osman Emre AYCAN

Aneurysmal bone cyst (ABC) is a benign but locally aggressive, expansile osteolytic lesion composed of blood-filled cavities separated by fibrous septa. It primarily affects children and young adults, typically in the first two decades of life, with no clear sex predilection. Although non-malignant, it can cause significant pain, swelling, and pathological fractures due to rapid growth and cortical thinning.

Epidemiology

• Accounts for approximately 1–2% of all primary bone tumors.
• Most common sites: long bones (femur, tibia, humerus) and posterior elements of the spine.
• Less frequently seen in the pelvis, clavicle, or small bones of the hands and feet.

Pathophysiology

The exact etiology remains unclear, but two forms are recognized:

1. Primary ABC – arises de novo, often associated with a translocation involving the USP6 gene (17p13), leading to osteolytic activity and vascular proliferation.
2. Secondary ABC – develops in association with another lesion such as giant cell tumor, chondroblastoma, osteoblastoma, or fibrous dysplasia.

The lesion consists of multiple blood-filled spaces without endothelial lining, separated by septa containing fibroblasts, osteoclast-type giant cells, and reactive bone.

Clinical Presentation

• Progressive pain, swelling, and restricted motion near the affected site.
• Palpable mass may be present.
• Pathologic fracture is a common first presentation in long bones.
• Neurological deficits can occur when lesions arise in the spine due to canal compression.

Imaging Features

Radiographs:

• Expansile, lytic lesion with “blow-out” or balloon-like appearance.
• Thin cortical shell and possible septations.
• May show fluid–fluid levels if internal hemorrhage is present.

MRI:

• Multiple fluid–fluid levels due to different blood degradation stages.
• Surrounding bone marrow edema and soft tissue extension are possible.
• Contrast enhancement in septa but not in cystic cavities.

CT:

• Useful for cortical evaluation and surgical planning.

Histopathology

• Multiple cystic spaces filled with blood, lacking endothelial lining.
• Septa contain fibroblasts, osteoid tissue, and multinucleated giant cells.
• No malignant cells are present.

Differential Diagnosis

Lesion                                                Distinguishing Features   

Telangiectatic Osteosarcoma   Malignant cells, atypia, and osteoid production   

Giant Cell Tumor (GCT)                Occurs after skeletal maturity, lacks fluid–fluid levels Chondroblastoma                         Epiphyseal location, presence of calcifications   

Fibrous Dysplasia                          Ground-glass matrix, lacks hemorrhagic cavities   

Simple Bone Cyst                           Single cavity, no septations, usually in metaphysis

Treatment

Management depends on lesion size, location, and aggressiveness:

• Extended curettage and high-speed burring – mainstay for most cases.
• Adjuvant therapies to reduce recurrence:Argon beam coagulation, phenol, or liquid nitrogen.
• Filling of cavity with bone graft or bone cement.
• Selective arterial embolization (SAE) – used for spinal or pelvic lesions or as preoperative adjunct.
• Percutaneous sclerotherapy (e.g., doxycycline or polidocanol) is increasingly used as a minimally invasive alternative.
• En bloc resection reserved for recurrent or inaccessible lesions.

Prognosis

• Recurrence rate: 10–30%, usually within the first two years post-treatment.
• Risk factors for recurrence include younger age, open physes, and incomplete excision.
• Long-term prognosis is excellent with appropriate treatment; malignant transformation is exceedingly rare.

Key Points

• ABC is a benign, vascular, expansile bone lesion with locally destructive potential.
• USP6 translocation confirms diagnosis in ambiguous cases.
• Fluid–fluid levels on MRI are suggestive but not pathognomonic.
• Minimally invasive approaches (e.g., sclerotherapy, embolization) show recurrence rates comparable to surgery in recent studies.
• Extended curettage with adjuvant remains the gold standard for accessible lesions in long bones.
• Recurrent cases may benefit from a combined strategy (embolization → curettage → bone graft).

References

1. Oliveira AM et al. USP6 Gene Rearrangement in Aneurysmal Bone Cyst. Am J Pathol. 2021;191(7):1210–1220.
2. Mascard E, Gomez-Brouchet A, Lambot K. Aneurysmal Bone Cyst: Clinical and Therapeutic Update. Orthop Traumatol Surg Res. 2015;101(1 Suppl)–S19.
3. Park HY et al. Treatment of Aneurysmal Bone Cysts: A Review of Current Concepts. J Bone Joint Surg Am. 2020;102(4):280–289.
4. Rastogi S et al. Percutaneous Doxycycline Sclerotherapy in Aneurysmal Bone Cyst. J Orthop Surg. 2019;27(3):2309499019878422.
5. Rapp TB et al. Aneurysmal Bone Cyst: A Review of Pathophysiology and Current Management. J Am Acad Orthop Surg. 2012;20(4):233–241.

Treatment Modality	Description / Technique	Recurrence Rate	Advantages	Limitations / Complications
Extended Curettage + Adjuvant (Phenol / Argon / Cryotherapy)	Thorough curettage of lesion cavity with mechanical and chemical adjuvant use	10–25%	Effective local control, joint preservation	Risk of growth plate injury or fracture
Curettage + Bone Graft / Bone Cement Filling	Cavity filled after curettage to provide stability	15–20%	Restores bone strength, simple procedure	Possible graft resorption, infection
En Bloc Resection	Complete excision with margin of healthy bone	<10%	Lowest recurrence rate	Loss of function, reconstructive need
Selective Arterial Embolization (SAE)	Preoperative or definitive occlusion of feeding vessels	10–20%	Minimally invasive, useful in spine/pelvis	Risk of incomplete occlusion, recurrence
Percutaneous Sclerotherapy (Doxycycline / Polidocanol)	Chemical ablation via multiple percutaneous injections	5–15%	Outpatient, minimal morbidity, excellent cosmetic results	Requires multiple sessions, rare skin necrosis
Radiotherapy (rarely used)	Reserved for inoperable or recurrent cases	Variable (~20%)	Non-surgical alternative	Radiation-induced sarcoma risk, growth disturbance

Treatment Options and Recurrence Rates in Aneurysmal Bone Cyst (ABC)