Orthopedics
InShort
AKA ABC
Aneurysmal bone cyst (ABC) is a benign neoplastic process that causes an aneurysmal-shaped deformity of the affected bone. ABCs may occur in any bone but are most commonly seen in the lower extremities during the second decade of life. The ABC expands locally and replaces normal bone with a vascular fibrous tissue and bone septa; this results in a weakened bone that is prone to fracture. ABCs can become quite large and can cause significant pelvic bleeding.
Causes and Risk Factors
ABCs originally were believed to be associated with intraosseous venous hypertension. Discovery of specific genetic markers (TRE17/USP6 oncogene translocation) recently have suggested a genetic predisposition to formation and, perhaps, recurrence of this tumor. ABCs also have occurred in the presence of other tumors (eg, chondroblastoma, osteoblastoma, chondromyxoid fibroma, giant-cell tumor).
Signs and Symptoms
Patients with ABC often present with bone pain that may be exacerbated with activity due to weakening of the bone and impending pathological fracture.
Diagnostic Evaluation and Differential Diagnosis
Plain radiographs usually are sufficient to identify ABCs and their soap-bubble appearance. However, biopsy may definitively differentiate ABC from other lesions (eg, unicameral bone cyst, giant-cell tumor) and potential malignant processes. The ABC has very prominent giant cells on microscopic evaluation.
Treatment and Recommended Follow-Up
Small, painless ABC's can be followed with periodic radiographs. ABC's in areas of bone that are highly loaded (ie, pelvis, femoral neck, knee) should be surgically debrided. Following intralesional or marginal resection, remaining bone surrounding the ABC should be treated with phenol, liquid nitrogen, laser therapy, or other adjuvant modality to reduce the rate of recurrence. The remaining cavity can be filled with autogenous bone graft or synthetic bone graft material.
Complications
Local bone pain may indicate ABC. Complications are primarily pathological fracture due to weakening of the bone and excessive surgical bleeding due to the rich vascular supply to these tumors. Recurrence of the tumor after simple curettage is not uncommon.
Pearl to Know
ABC's can be locally aggressive, especially after local recurrence.
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