Jaffe and Lichtenstein1 described
aneurysmal bone cyst as a benign non-neoplastic lesion of unknown
etiology. Aneurysmal bone cysts can be primary or secondary to other
bone tumors, including nonossifying fibroma, chondroblastoma, giant-cell
tumor of bone, osteoblastoma, fibrous dysplasia, fibromyxoma, osteoblastoma,
solitary bone cyst, hemangioendothelioma, osteosarcoma, and metastatic
carcinoma2,3.
Although several cases of malignant transformation have been reported,
most were either radiation-induced sarcomas or telangiectatic osteosarcomas
that had been misdiagnosed as aneurysmal bone cyst. To our knowledge,
the literature contains only one report of satisfactorily documented
malignant transformation of an aneurysmal bone cyst4.
We describe a patient who had a malignant fibrous histiocytoma
at the site of a femoral aneurysmal bone cyst that had been treated
twelve years earlier by curettage and internal fixation after a
pathological fracture.
A twenty-eight-year-old man was admitted to our institution in
December 1986 because of a pathological supracondylar fracture of
the left femur. Anteroposterior and lateral tomograms revealed a
pathological fracture in the distal part of the left femur through
a large lytic lesion in the diaphysis and epiphysis (Fig. 1). There was
no periosteal reaction. The limb was placed in an above-the-knee
cast. No evidence of metastasis was seen on a computed tomographic
scan of the chest, and a technetium-99m polyphosphate bone scan
showed a single focus of hyperactivity only at the site of the pathological
fracture. Routine laboratory data were normal.
An open biopsy of the femoral lesion was performed. Histological
examination revealed the typical features of an aneurysmal bone
cyst, with multiple blood-filled cavities separated by fibrous septa
containing osteoid, giant cells, and fibroblasts (Figs. 2-A and 2-B).
Extensive, meticulous curettage followed by implantation of a morselized
allograft and internal fixation was performed three weeks later
(Fig. 3).
The limb was immobilized in an above-the-knee cast for two months.
No adjuvant treatment was given.
Regular follow-up until 1994 showed no clinical or radiographic
evidence of recurrence. However, the patient sought medical advice
in February 1998 because of persistent pain in the left knee. Physical
examination revealed a small effusion. The active range of flexion
was 0 to 125. Bacteriological cultures of fluid aspirated from the
knee were negative. The effusion failed to respond to nonsteroidal
anti-inflammatory therapy.
Radiographs of the distal part of the femur showed an osteolytic
lesion, but the bone architecture had been profoundly modified by
the previous surgery. Because the patient had a history of aneurysmal
bone cyst, a computed tomographic scan was performed to rule out
a local recurrence. The scan revealed a large metaphyseal osteolytic
lesion with destruction of the anteromedial cortex (Fig. 4). Magnetic resonance
imaging was not feasible because of the presence of the internal
fixation.
These findings were interpreted as consistent with a local recurrence
of the aneurysmal bone cyst or with subacute osteomyelitis presenting
as a bone tumor twelve years after the initial curettage procedure.
A surgical biopsy of the femoral bone lesion was performed. Cultures
were negative. Histological examination demonstrated a malignant
fibrous histiocytoma of the storiform-pleomorphic type. This tumor
was characterized by a proliferation of spindle cells in a storiform
pattern admixed with bizarre, large pleomorphic cells. Scattered
inflammatory cells were seen in the background (Figs. 5-A and 5-B). A flow cytometry
DNA study demonstrated aneuploidy (DNA index, 2.37). A diagnosis
of nonmetastatic grade-3 malignant fibrous histiocytoma at the site
of the previous aneurysmal bone cyst was made. The initial treatment,
which was continued for four months, consisted of five cycles of
OS 5 chemotherapy (a combination of Adriamycin [doxorubicin], platinum,
mesna, and cyclophosphamide, given for two days every three weeks).
In July 1998, the distal part of the femur was resected and was reconstructed
with use of a custom-made prosthesis. The gross appearance was that
of a metaphyseal and epiphyseal mass measuring 8.5 6.5 6 cm and
exhibiting hemorrhagic necrotic areas (Fig. 6). Histological examination confirmed
the diagnosis of malignant fibrous histiocytoma and showed 95% chemotherapy-induced
tumor necrosis. After completion of three additional cycles of OS
5 chemotherapy, the functional result was satisfactory.
At the last follow-up examination, in February 2000, the patient
was alive with no evidence of disease.