Summary
The expansile nature of this lesion may be very striking and the bone may be many times larger than normal.
Complete Information on this Tumor
ABC's may be secondary to an underlying lesion such as non-ossifying fibroma, chondroblastoma, osteoblastoma, UBC, chondromyxoid fibroma and fibrous dysplasia. The lesion should be examined microscopically in several places to eliminate the possibility of a primary lesion. In the author's experience, ABC seems to be a primary lesion. However, we are aware of one case where aneurysmal bone cyst was diagnosed by biopsy and confirmed after curettage. Following this a destructive lesion developed and an osteosarcoma was diagnosed. Caution is advised.
In one report (Kransdorf, Amer J Roentgenol 1995 Mar;164(3):573-80) the authors state that the original lesion can be identified in one-third of cases. The most common precursor lesion was giant cell tumor, (19-39%) of cases, followed by osteoblastoma, angioma, and chondroblastoma. Less common precursor lesions were fibrous dysplasia, non-ossifying fibroma, chondromyxoid fibroma, unicameral bone cyst, fibrous histiocytoma, eosinoplilic granuloma, and osteosarcoma. A translocation involving the 16q22 and 17p13 chromosomes has been identified in the solid variant and extraosseous forms of aneurysmal bone cyst.
The most common location is the metaphysis of the lower extremity long bones, more so than the upper extremity. The vertebral bodies or arches of the spine also may be involved. Approximately one-half of lesions in flat bones occur in the pelvis.
In the foot, ABC is uncommon. Observed locations include the metatarsals or midfoot.
There may be a history of trauma and some have postulated a causative link between trauma and this lesion. Patients complain of pain and a slow growing mass.
The radiographic appearance may be strikingly aggressive in the early phase of growth, but after a few weeks the margin of the lesion becomes better defined and the appearance is less worrisome. The highly expansile lesion perched at the end of the bone has been described with the catchphrase "finger in a balloon." Most patients in the USA will receive treatment well before the tumor reaches this stage, so the catchphrase may be of historical value only.
MRI may show fluid-fluid levels within the lesion, which may demonstrate multiple seperate loculations or one large loculated cavity, and these can be highly suggestive of the diagnosis but are not diagnostic. CT and bone scan are not helpful in diagnosis but may help define the lesion or rule out multiple lesions.
If a recurrence is detected, a thorough examination of the original radiographs and pathology specimens should be performed to insure that the primary lesion, if any, is discovered, since this may radically alter the treatment plan. Once the precise diagnosis is known, local recurrences may be retreated by appropriate methods.
