Benign Bone Tumors of the Foot - Section 3

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Aneurysmal bone cyst

Aneurysmal bone cyst fresents 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. 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."

MRI may show fluid-fluid levels within the lesion, 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.

Microscopically, the ABC has cystic spaces filled with blood. The fibrous septa have immature woven bone trabeculae as well as I macrophages filled with hemosiderin, fibroblasts, capillaries and giant cells. ABC's can be secondary to an underlying lesion such as non-ossifying fibroma, chondroblastoma, osteoblastoma, UBC's, chondromyxoid fibroma and fibrous dysplasia. This association is so strong that the lesion should be examined microscopically in several places to eliminate the possibility of a primary lesion.

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 authors have seen one case where aneurysmal bone cyst was diagnosed by biopsy and confirmed after curettage. Following this a destructive lesion developed and and an osteosarcoma was diagnosed. Caution is advised.

Most lesions can be treated with currettage and application of a high-speed burr. 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 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.

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.

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.

Giant cell tumor

Giant cell tumor is relatively uncommon in the foot. The incidence is highest in the third decade and the lesions are located in the metaphysis adjacent to the epiphysis or epiphyseal scar. For this reason, the lesions are located proximally in the first metatarsal and distally in the lesser metatarsals due to the location of the epiphysis.

Patients have pain and a mass, and pathological fracture may occur. Plain radiographs show a lytic lesion without matrix mineralization in the above-named location. The cortex may be expanded and even destroyed.

Treatment consists of "extended curettage" and filling of the lesion with a suitable material, such as morcellized bone graft, bone graft substitute, or polymethylmethacrylate bone cement. Highly expansile primary lesions of the lesser bones of the foot may be excised and grafted from the iliac crest with excellent results. Lesions of the phalanges of smaller the lesser toes should be amputated.

An "extended curettage" is performed by mechanical currettage plus the application of adjuvant local treatment, such as liquid nitrogen, phenol, or a high speed burr. In this way potential microscopic amounts of tumor tissue that may be present in the margins of the curetted cavity are eliminated, and the rate of local recurrence is reduced. Local recurrence may be treated by repeat extended curettage, or if local control seems impossible, by wide excision and reconstruction with a bone graft.

Pathology of giant cell tumor:

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