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Aneurysmal bone cyst - Foot and Ankle

Summary

The expansile nature of this lesion may be very striking and the bone may be many times larger than normal.

Aneurysmal bone cyst presents in the second and third decade.
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.
Lesions are located on the surface of the bone as well as in the metaphysis or epiphysis. Plain radiographs show an expansile lesion with internal septae or longitudinal striations.
Most lesions can be treated with currettage and application of a high-speed burr.
Complete Information on this Tumor
Introduction and Definition: 

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.

Incidence and Demographics: 
Aneurysmal bone cyst presents in the second and third decade.
Symptoms and Presentation: 

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.

X-Ray Appearance and Advanced Imaging Findings: 
Lesions are located on the surface of the bone as well as in the metaphysis or epiphysis. Plain radiographs show an expansile lesion with internal septae or longitudinal striations. The expansile nature of this lesion may be very striking and the bone may be many times larger than normal. Even in highly expanded lesions, there is a thin eggshell laver of reactive bone on the surface of the lesion. This layer may be poorly mineralized in active lesions that are still growing and become more apparent as the lesion matures. 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.
Histopathology findings: 
Microscopically, the ABC has cystic spaces filled with blood. The fibrous septa have immature woven bone trabeculae as well as macrophages filled with hemosiderin, fibroblasts, capillaries and giant cells.
Treatment Options for this Tumor: 
Most lesions can be treated with currettage and application of a high-speed burr. The lesions may bleed freely until completely excised. Curettage and bone graft can be complicated by profuse bleeding from the lesion. The authors have not seen exccessive bleeding from lesions from the foot. Radiation has been used in some cases where operative treatment is not possible, but this adds the additional risk of malignancy.
Outcomes of Treatment and Prognosis: 
Local recurrence rates vary widely, with one recent report having 4 recurrences in 40 patients (Gibbs JBJS Am 1999 Dec;81(12):1671-8). Recurrence rates may be as high as 20%. Recurrence was statistically related to young age and open growth plates, and may be less likely following wide excision than following intralesional treatment by currettage. 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.
Special and Unusual Features: 
The authors have not seen conventional aneursmal bone cyst in the foot, but they have seen cases of the solid variant of aneurysmal bone cyst both in the forefoot and the midfoot.
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