Aneurysmal Bone Cysts

Aneurysmal bone cysts (ABCs) are benign lesions of bones that primarily affect young people; 80% of patients present under the age of 20. There is no sex predilection. While ABCs can occur at any location, 90% are seen in the spine. Within the spine, most lesions involve the posterior elements, although the vertebral body can also be involved. Additionally, ABCs (in addition to vertebral hemangiomas) can involve two contiguous vertebral bodies.28

The radiographic appearance of ABCs has been well described. Pathologically, the lesions consist of enlarged communicating spaces within the bone, containing venous blood under higher than normal venous pressure. The lining of the spaces consists of a fibro-osseous patchwork and some giant cells.28 Interestingly, up to one third of ABCs are found in conjunction with other lesions, such as fibrous dys-plasia, osteoblastoma, or chondrosarcoma,29 and others may be associated with previous trauma.30

With regard to pathogenesis, most authors believe that a hemody-namic imbalance or abnormality within the bone is the etiological factor, especially with regard to impaired venous drainage.30,31 Some have suggested the presence of a congenital vascular abnormality in cases of de novo ABCs, and impairment of venous drainage by a secondary factor (associated lesions, or trauma) in other cases.30

Angiographically, there is no pathognomonic pattern for ABCs. Findings can vary from faint or moderate vascularity to dense vascu-larity with a rich network of dilated, tortuous feeding vessels and a dense stain of the lesion within the vertebral body.28 Djindjian described arteriovenous shunting in some lesions,14a while others have described patchy collections of contrast within the cystic spaces, persisting into the late venous phase.

Therapy

The most common approach to symptomatic ABCs is surgery, whether with curettage or with resection of the lesion and reconstruction of the spine if necessary. In many cases, owing to the vascularity of the lesion, the operating surgeon will request preoperative angiography and embolization of the lesion to decrease intraoperative blood loss, which can be significant (Figure 16.6).

At least two separate papers have described the successful use of en-dovascular embolization as the sole therapy for ABCs. Cigala and Sadile32 described the results of embolization of six large ABCs in children, in whom operative therapy would have been difficult. Long-term follow-up showed almost complete healing of the lesions and restoration of the normal shape of the affected bone. None of the patients required subsequent surgery. Radanovic et al.33 described the endovas-cular embolization of ABCs in five patients, all of whom had relief of their primary symptom (pain) and a decrease in size of the ABC. In patients who were followed up for more than 12 months, sclerosis and recalcification of the lesions was described.

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