[Aneurysmal bone cyst in 2006].

The etiology of aneurysmal bone cyst is probably multifactorial. Recent progress in genetics and immunohistochemistry tends to prove that aneurysmal bone cyst is tumor and not a pseudo-tumor. Involvement of chromosomes 17p11-13 or 16q22 has been described. MRI is indispensable. Signs highly suggestive of aneurysmal bone cyst are: well-limited expansive bone lesion, low intensity T1 signal associated with high intensity T2 signal (liquid component), a low intensity peripheral line with enhancement after contrast injection, septal partitioning and fluid levels. Gadolinium injection is informative since it demonstrates the thick regular septal partitioning and the amorphous contents (lack of contrast uptake), a structure which is not seen in any other tumors, particularly malignant tumors. Plain x-ray and MRI contribute well to diagnosis but histological confirmation is always required. The debate on Ethibloc(R) remains open. For certain authors, this technique is an effective safe treatment which can be proposed as a first-line option. Ethibloc(R) should however be reserved for specialized teams because of the serious complications reported in the literature. A new treatment has also been reported to be promising, but further results will be required for confirmation. With this technique demineralized allogenic bone particles associated with autologous bone marrow are implanted in the cyst to achieve an osteogenic effect. This induces the cyst to pass from the destructive resorption phase to the repairing osteogenic phase. Curettage is not necessary. This method, which avoids extensive surgery and blood loss, is well adapted to difficult localizations such as the pelvis.