Introduction

Aneurysmal bone cysts are vascular lesions consisting of widely dilated vascular channels that are not lined by identifiable endothelium and account for 1% to 2% of all benign bone lesions.

Etiology

The etiology of aneurysmal bone cysts is not certain. In most instances, they are primary lesions; occasionally they are secondary to or associated with other lesions, such as unicameral bone cyst, nonossifying fibroma, fibrous dysplasia, or osteogenic sarcoma.

Clinical Findings

Aneurysmal bone cysts involve the long bones in 75% of patients. In order of decreasing frequency, the most commonly involved long bones are the distal femur, proximal tibia, proximal humerus, and distal radius. Vertebral involvement is seen in 12% to 27% of patients; the lumbar vertebrae are most commonly affected.  The patients usually complain of a mild, dull pain of several weeks' or months' duration, and only rarely is there a clinically apparent pathologic fracture. When the cyst involves the spine, progressive enlargement may compress the spinal cord or nerve roots, resulting in neurologic deficits such as motor weakness, sensory disturbance, and loss of bowel and bladder control.

Radiographic and Histologic Features

Table below presents the typical radiographic and histologic features of aneurysmal bone cysts while comparing it to the Unicameral bone cysts.

Treatment

Although aneurysmal bone cysts have a well-differentiated benign histology, most are aggressive and grow and invade rapidly, treatment should be prompt once the diagnosis is made. The initial step in the effective treatment of a patient with an aneurysmal bone cyst is to confirm the diagnosis. This is accomplished with biopsy and frozen section. The biopsy may be done in the same surgical setting as the definitive surgical procedure. Surgical management includes curettage, thermal coagulation with a cautery, thorough excision of the lining with use of a high-speed burr, and, occasional use of adjuvant therapy (e.g., hydrogen peroxide or phenol) for some of the aggressive or recurrent aneurysmal bone cysts.

Large lesions may be additionally bone grafted (autograft, allograft, bone substitutes, or a combination of these). Large lesions located in high-stress locations (e.g., proximal femur) and/or associated with unstable pathologic fractures may require additional stabilization with hardware. Aneurysmal bone cysts in bones, such as fibula, ribs, distal ulna, metacarpal, and metatarsal bones, may be treated by en bloc resection. Sometimes resection may be appropriate for recurrent aggressive lesions.

Radiation therapy should be avoided because it has been associated with later development of sarcoma. It also may damage reproductive organs and the active growth areas of long bones and cause other complications. Selective arterial embolization can be used as definitive treatment or preoperatively with other procedures. It is used most commonly in the spine, pelvis and sacrum (Hosalkar et al Spine. 2007 ;32:1107-15), and the proximal portion of the extremities when surgical exposure is more difficult and invasive and when blood loss with standard surgery can be significant.

An aneurysmal bone cyst of the spine can present as a complex and challenging problem. The location of the lesion most commonly involves the posterior vertebral elements but it may extend anteriorly into the vertebral body. Surgery is recommended for all patients as the initial means of treatment. Most cases are controlled with simple curettage; the posterior elements are resected, and involvement of the pedicles or the body is curetted. If there is a question of iatrogenic instability related to the excision then a short posterior fusion is advised.