Aneurysmal Bone Cyst (ABC)

Modern Study Review (AI-Generated)

High-Yield Summary

Aneurysmal Bone Cyst (ABC) is a benign, expansile, osteolytic bone lesion predominantly affecting children and young adults in their second decade. It typically involves the metaphysis of long bones, flat bones, and vertebrae, presenting with pain, swelling, and characteristic radiologic features. Accurate differentiation from malignant mimics like telangiectatic osteosarcoma is critical. Treatment focuses on local control via curettage and bone grafting, with adjunctive therapies to reduce recurrence.

Key Diagnostic Findings

Anatomy

• Predominantly metaphyseal location in long bones (femur, tibia), flat bones (pelvis, scapula), and vertebrae.
• Lesion is expansile and eccentric, often causing cortical thinning and periosteal reaction.

Clinical Presentation

• Age: Most common in the 2nd decade of life.
• Symptoms: Localized pain, tenderness, swelling, and sometimes pathological fracture.

Imaging

Histology

• Blood-filled cystic spaces separated by cellular septa without endothelial lining.
• Septa contain fibroblasts, multinucleated giant cells, histiocytes, and metaplastic woven bone.
• May have solid cellular areas, but lacks malignant features.

Classification Systems

• No widely used formal classification system; diagnosis is primarily radiologic and histologic.
• Important to differentiate from telangiectatic osteosarcoma (malignant).

Current Gold Standard Treatment

Non-operative

• Observation may be considered in asymptomatic, stable lesions without risk of fracture or neurological compromise (rare).
• Selective arterial embolization can be used as adjunct or primary treatment in difficult anatomical locations (e.g., spine, pelvis).

Operative

• Indications: Pain, progressive lesion size, risk of fracture, neurological symptoms (spinal ABC), or pathological fracture.
• Treatment: Intralesional curettage with high-speed burring and bone grafting (autograft or allograft).
• Adjuncts: Cryotherapy or chemical adjuvants (phenol, argon beam) to reduce recurrence risk.
• En bloc resection reserved for recurrent or aggressive lesions but limited by morbidity.

Modern Complications & Outcomes

Complications

Outcomes

• Generally excellent with appropriate surgical management.
• Recurrence rates have decreased with use of adjuvant therapies.
• Functional outcomes focus on pain relief and restoration of structural integrity.
• Long-term surveillance recommended for early detection of recurrence.

Classic Clinical Notes

Aneurysmal Bone Cyst (ABC)

• Solitary expansile lesion located in metaphysis of long bones, flat bones & vertebrae
• Presents in 2nd decade
• Cysts filled with blood

Signs & Symptoms:

• Pain with tenderness & swelling at the site of the lesion

X-rays:

• Expansile eccentric lesion surrounded by a thinned cortex with periosteal new bone formation
• CT/MRI – characteristic ‘fluid-fluid’ level
• Beware of telangiectatic osteosarcoma – has fluid-fluid levels but far more aggressive looking

Histology:

• Blood spaces separated by cellular septa lacking an endothelial cell lining & containing a variety of cells such as fibroblasts, multinucleated giant cells & histiocytes & metaplastic bone
• Large solid cellular areas may be seen

Treatment:

• Excision, curettage & bone grafting
• Cryosurgery or chemical ablation may be used

Last Updated on January 25, 2026 by orthonet