Aneurysmal Bone Cyst (ABC)
Aneurysmal Bone Cyst (ABC) is not a true benign tumor of bone, rather a vascular and reactive malformation which is usually single, expansive and aggressive lesion. It is most commonly seen in age group of 15-25 years, but can be found in any age. It is found in the metaphysis and epiphyseal location, commonly in long bones (upper extremity > lower extremity) followed by pelvis.
What is the cause of ABC?
The etiology of ABC is unknown. It is suspected to be related to trauma. It is also found as a secondary component of other tumors such as Giant cell tumor, Chondroblastoma, Fibrous dysplasia, Osteoblastoma and rarely even in Osteosarcoma.
How is ABC identified?
An individual with ABC will present with pain or swelling of duration of several weeks. Pathological fracture is common due to aggressive nature of ABC and involvement of weight bearing bones.
Plain radiographs show a solitary, expanded cavity which has destroyed surrounding bone. ABC have tendency to expand beyond the original structure of involved bone giving it a Soap-Bubble kind of appearance. MRI is necessary to diagnose ABC, and typical finding is Multiple Fluid levels. Biopsy (Needle) is mandatory to diagnose ABC as it can mimic any of the other benign or even malignant bone tumors. Pathological examination shows blood filled cyst cavities with giant cells.
How is ABC treated?
Treatment of ABC depends upon location and aggressiveness of lesion. Very few ABC’s can be in latent or inactive stage. These when identified can be treated with percutaneous curettage (Curopsy) or by Percutaneous Sclerotherapy (polidocanol, 2 %) under radiological guidance, usually in 2-3 visits with average healing time of 5 months. They are also treated surgically with Extended Curettage to clear tumor followed by filling or reconstruction of the defect similar to GCT or UBC. Adjuvants can be used, but there is no clear evidence of benefit. In situations where the ABC is large or in sites such as pelvis and spine, Percutaneous Serial Arterial Embolization can be carried out with aid or Interventional Radiologist with good results to decrease the size of tumor or even as a primary mode of treatment in inoperable situations. Recently, there has been a shift in treating ABC’s by minimally invasive surgical procedures like Curopsy and/or Sclerotherapy, due to similar results noted between surgical and minimally invasive procedures. In some situations, when the tumour has grown so large, resulting in pathological fracture or when the bone is not salvageable, a resection and reconstruction procedure (biological or Tumor endoprosthesis) is carried out.
Does ABC reappear/recur ?
The recurrence rate in long bones after curettage alone is 20-35 % which can be reduced by performing extended curettage resulting in risk of local recurrence at 10 %. Similar rates of recurrence are being observed when ABC’s are being treated by Curposy and/or Sclerotherapy. ABC is aggressive and may add to morbidity but it does not metastasize and is not fatal. Adjuvant treatment with Zoledronic acid or Denosumab is encouraging but has limited scientific data.