Aneurysmal bone cysts

Overview

An aneurysmal bone cyst is a blood-filled fibrous tumor-like cyst that expands the bone, giving it a "blow-out" appearance. It typically occurs in the second decade of life and can emerge in virtually any bone in the arms, legs, trunk or skull. The vertebrae and knee are the most common sites of occurrence. An aneurysmal bone cyst is a benign bone tumor, meaning that it does not metastasize (spread) to other regions of the body. It can however be quite destructive locally and has a high propensity for recurrence.

When it occurs in bones of a limb, it typically involves any of the following areas of the bone:

  • Metaphysis - the transitional zone where the shaft of the bone joins the end of the bone
  • Diaphysis (shaft)-bone near the growth plate (the area of the bone in which growth occurs)

When it occurs in the spine, the cyst can grow to involve the entire vertebral body where it arose or it can involve the adjacent vertebrae. Generally, those cysts considered "active" could deform the host bone but remain contained in the bone, while others, considered "aggressive" extend beyond the bone to the adjacent soft connective tissues. Rarely will these types of cysts resolve on their own without treatment.

Symptoms

Every child experiences symptoms differently. Symptoms include:

  • Pain
  • Swelling
  • A mass that can be felt (sometimes)
  • Mild to severe neurological problems (if cyst is in spine)
  • Fracture caused by the cyst (rarely) The symptoms of an aneurysmal bone cyst resemble symptoms of other conditions or medical problems. Always consult a physician for a diagnosis.

Causes

Aneurysmal bone cyst has been widely regarded a reactive process of uncertain etiology since its initial description by Jaffe and Lichtenstein in 1942. Many hypotheses have been proposed to explain the etiology and pathogenesis of aneurysmal bone cyst, and until very recently the most commonly accepted idea was that aneurysmal bone cyst was the consequence of an increased venous pressure and resultant dilation and rupture of the local vascular network. However, studies by Panoutsakopoulus et al. and Oliveira et al. uncovered the clonal neoplastic nature of aneurysmal bone cyst. Primary etiology has been regarded arteriovenous fistula within bone.

The lesion may arise de novo or may arise secondarily within a pre-existing bone tumor, because the abnormal bone causes changes in hemodynamics. An aneurysmal bone cyst can arise from a pre-existing chondroblastoma, a chondromyxoid fibroma, an osteoblastoma, a giant cell tumor, or fibrous dysplasia. A giant cell tumor is the most common cause, occurring in 19% to 39% of cases. Less frequently, it results from some malignant tumors, such as osteosarcoma, chondrosarcoma, and hemangioendothelioma.

Diagnosis

When making a diagnosis, your child's doctor will also want to know how aggressive the tumor is. In addition to performing a physical examination and taking a medical history, the doctor will want your child to undergo one or more of the following diagnostic tests:

  • X-rays - a diagnostic test that uses invisible electromagnetic energy beams to produce images of internal tissues, bones, and organs onto film.
  • Magnetic Resonance Imaging (MRI) - a diagnostic procedure that uses a combination of large magnets, radiofrequencies and a computer to produce detailed images of organs and structures within the body. This test is particularly useful to confirm the diagnosis by demonstrating the characteristic fluid levels within the cyst.
  • Computerized Tomography scan (also called CT or CAT scan) - a diagnostic imaging procedure that uses a combination of x-rays and computer technology to produce cross-sectional images (often called slices) both horizontally and vertically, of the body. A CT scan shows detailed images of any part of the body, including the bones, muscles, fat and organs. CT scans are more detailed that general x-rays. This test is also particularly useful in confirming the diagnosis by demonstrating the characteristic fluid levels within the cyst.
  • Bone scan - a test that uses an injection of an isotope (small dose of radioactive material) that seeks out all bones of the skeleton. It tells the doctor whether there are other tumor sites (although this would be unusual in aneurysmal bone cyst).

Differential diagnosis:
Following conditions are excluded before diagnosis can be confirmed:

  • Unicameral bone cyst
  • Giant cell tumor
  • Telangiectatic osteosarcoma
  • Secondary aneurysmal bone cyst

Prognosis

Recurrence rate of solid form of tumour is lower than classic form.

Treatment

Treatment for the cyst will likely involve one or a combination of the following surgical procedures performed by a pediatric orthopaedic surgeon. 

Curettage is performed on some patients, and is sufficient for inactive lesions. The recurrence rate with curettage is significant in active lesions, and marginal resection has been advised. Liquid nitrogen, phenol, methyl methacrylate are considered for use to kill cells at margins of resected cyst.