Aneurysmal Bone Cysts (ABC’s) Dr. Ted Scriven Sept 8, 2008

ABC’s Classified as a benign boney lesion More specifically, “benign-aggressive” Benign-aggressive = marked bone destruction, soft tissue extension or pathologic fractures

Etiology Specific translocation @ 17p13 Can arise de novo, or be associated with another primary: GCT, chondroblastoma, UBC, osteoblastoma, fibrous dysplasia, nonossifying fibroma, chondromyxoid fibroma, osteosarcoma

Increased venous pressure Etiology Result from local circulatory abnormality: Increased venous pressure Local hemorrhage Osteolysis More bleeding Source of bleeding = capilliaries in cyst membrane Hemorrhage progresses to destructive lesion

Clinical Picture Age: often < 20 Gender: F > M (slight) Location: metaphysis or metadiaphysis of long bones (prox humerus, distal femur, prox tibia) Occasionally iluim or lumbar vertebrae (15 – 20%)

Clinical Picture Mild pain or swelling May have neuro deficits with spinal lesions Duration = weeks  years Symptoms may worsen with pregnancy (more blood volume)

Investigations Start with thorough Hx & PE Xray: Radiolucent destructive cyst, expands surrounding cortex  “Soap-Bubbles” Often eccentric, can be central or subperiosteal Elevated periosteum Thin shell

Investigations Bone Scan: Angiography: Diffuse or peripheral tracer uptake Central area of decreased uptake Angiography: Accumulation of contrast throughout +/- hypervascularity of periphery Absence of viable afferent or efferent vessels

Investigations CT Helps deliniate lesion in areas of complex boney anatomy MRI Multiloculated cavities, fluid levels, +/- associated soft tissue mass Helps to differentiate between ABC & UBC

DDx UBC Chondromyxoid Fibroma Chondroblastoma GCT Osteoblastoma Talengiectatic Osteosarcoma

Pathology Gross: Cavitary w/ blood filled spaces Surrounded by thin layer of bone & raised periosteum

Pathology Micro: Hemorrhagic tissue with spaces separated by cellular stroma No endothelial lining or smooth muscle – only lining is compressed fibroblasts ALWAYS be sure to examine entire speciman and surrounding area (association with other primaries!!)

Treatment Curettage & Bone Grafting Caution: lesion prone to heavy bleeding! Tourniquet Pre-op embolization +/- local adjuvent tx for cavity sterilization: Phenol, liquid nitrogen, argon Ressection: If area is expendable (fibula, metatarsal, etc) Radiation: Not routinely used d/t potential for malignant transformation

Prognosis If primary: If associated with another primary: Usually a favourable prognosis Recurrence: Rate after curettage = 14 – 34% Usually within 6/12, rare after 2 yrs More common in age < 15 yo, centrally located lesions, and when contents not all removed If associated with another primary: Classification, treatment and prognosis based on the other (primary) lesion