Aneurysmal Bone Cyst - Pathology

Introduction

A benign and non-neoplastic reactive bone lesion filled with multiple blood-filled cavities
- can be locally destructive to normal bone and may extend to soft tissue
Epidemiology
- demographics
  - 75% of patients are < 20 yrs.
- location
  - 25% in spine
  - 20% in long bones (distal femur, proximal tibia)
  - usually in metaphysis
  - metatarsal is the most common location in the foot
  - posterior elements of pelvis
  - may be found in similar location as telangiectatic osteosarcomas
Pathophysiology
- primary and secondary forms
  - primary ABC:
    - now known to be neoplasms driven by upregulation of the ubiquitin-specific protease USP6 (Tre2) gene on 17p13 when combined by translocation with a promoter pairing
    - most commonly described translocation t(16;17)(q22;p13) leading to juxtaposition of promoter region CDH11 on 16q22
  - secondary ABC:
    - not considered a neoplasm because no known translocation has been identified
Associated conditions
- associated with other tumors 30% of time
  - giant cell tumor
  - chondroblastoma
  - fibrous dysplasia
  - chondromyxoid fibroma
  - NOF
Prognosis
- good

Presentation

Imaging

Radiographs
- expansile, eccentric and lytic lesion with bony septae ("bubbly appearance")
- usually in metaphyseal
- classic cases have thin rim of periosteal new bone surrounding lesion
- no matrix mineralization
MRI or CT scan
- will show multiple fluid lines
- lesion can expand into soft tissue

Studies

Differential

Radiographic differential includes
- UBC
- telangiectatic osteosarcoma
Histologic differential includes
- telangiectatic osteosarcoma
- giant cell tumor

Treatment

Nonoperative
- nonoperative fracture management
  - indications
    - ABC with acute fracture
      - indicated until fracture has healed. Once healed, treat as an ABC without fracture unless the fracture has led to spontaneous healing of the ABC
Operative
- aggressive curettage (+/- adjuvant) and bone grafting
  - indications
    - symptomatic ABC without acute fracture
  - technique
    - possible adjuvants
      - phenol
      - argon beam
      - liquid nitrogen
  - outcomes
    - local recurrence in up to 25% and more common in children with open physes

Differential & Groups

	"Bubbly" lytic lesion on xray	"Lakes of Blood" on histology	Treatment is curretage and bone grafting (1)
Aneurysmal Bone cyst	•	•	•
UBC	•
NOF	•
Giant Cell Tumor			•
Chondroblastoma			•
Chondromyoid fibroma			•
Osteoblastoma			•
Telangiectatic osteosarcoma		•
ASSUMPTIONS: (1) assuming no impending fracture

IBank

	Location	Xray	Xray	CT	B. Scan	MRI	MRI	Histo(1)
Case A	tibia
Case B	calcaneus
Case C	pelvis
Case D	femur
Case E	femur
(1) - histology does not always correspond to clinical case