Synonyms

ABC

Category

Bone

Behaviour

Intermediate

Gender

Both equally

Tissue of Origin

Bone

Epidemiology

• Common Benign Bone lesion, 1–6% of primary Bone tumours
• Peak incidence in 1st and 2nd decades (80% <20 years)
• Can be primary (de novo) or secondary (arising within another lesion)

Clinical Features

• Pain and swelling at affected site
• Pathological fracture in 20% of cases
• Rapid growth may mimic malignancy
• Spinal lesions: neurological compromise

Location

• Metaphysis of long Bones (femur, tibia, humerus) most common
• Posterior elements of spine
• Flat Bones (pelvis, ribs)
• Jaws (maxilla/mandible)

Imaging

• Expansile eccentric lytic lesion with trabeculation (soap-bubble appearance)
• Fluid-fluid levels on MRI - hallmark finding
• Cortical thinning but intact periosteal shell
• Bone scan: hot periphery (doughnut sign)

Pathology

• Blood-filled cystic spaces separated by Fibrous septa
• Septa contain osteoid, giant cells, and reactive Bone
• No endothelial lining to cystic spaces
• Solid variant ('solid ABC') may be confused with GCT or sarcoma

Genetics

• USP6 gene rearrangement in 70% of primary ABCs
• Partner genes: CDH11 (most common), THRAP3, ZNF9, COL1A1
• Secondary ABCs lack USP6 rearrangement

Treatment

• Curettage and Bone grafting - first-line
• Extended curettage with adjuvants reduces recurrence
• Selective arterial embolisation - effective and may be used alone or as adjunct
• Denosumab - emerging role, especially in surgically difficult locations
• Doxycycline sclerotherapy for selected cases

Prognosis

• Recurrence rate 15–30% after simple curettage
• Lower recurrence with extended curettage (10%)
• No Malignant transformation of primary ABC
• Secondary ABC prognosis determined by underlying lesion

Key Points

• Fluid-fluid levels on MRI are characteristic but not pathognomonic
• USP6 FISH useful to confirm primary ABC vs secondary
• Must exclude telangiectatic osteosarcoma - shares imaging features
• Sclerotherapy and embolisation effective alternatives to surgery

Workup - Blood Tests

No blood tests required

Workup - Local Imaging

• Plain radiograph
• CT
• MRI

Workup - Biopsy

• Biopsy if diagnosis uncertain
• Histology: blood-filled spaces with haemosiderin-laden macrophages
• Cavovid nodular lesion with osteoid at septa

Follow-up Summary

• Post-op visit within 6 weeks; plain radiograph to establish baseline
• Year 1: 3–6 monthly clinical review + plain X-ray of primary site; MRI if recurrence suspected
• Year 2: 6-monthly review; imaging only if symptomatic or clinical concern
• Years 3–5: Annual review; discharge if no recurrence and primary ABC confirmed (not secondary)
• Discharge supported if: complete healing, no recurrence at 2 years, asymptomatic
• Secondary ABC: Follow-up determined by underlying lesion
• Red flags: return of pain/swelling, pathological fracture - warrants urgent MRI