Aneurysmal bone cyst is an expansile, destructive, hemorrhagic,
non-neoplastic lesion that is thought to represent a benign reactive vascular
process1-4.
These lesions have been designated as either primary or
secondary, with the latter term used when histological evaluation
indicates a coexisting lesion, which can be either benign or
malignant5,6.
Occasionally, telangiectatic osteosarcomas have been misdiagnosed as
aneurysmal bone
cysts7-9,
but the true nature of the malignant tumors usually became apparent after
rapid progression or
recurrence7. Like
other benign tumors, aneurysmal bone cysts have been reported to have
undergone malignant transformation, although most of the transformations were
induced by
irradiation7,10,11.
In a review of the literature, only two well-documented reports of malignant
transformation of an aneurysmal bone cyst without a history of irradiation
were found. One transformation was to a malignant fibrous histiocytoma, and
the other was to an
osteosarcoma7,12.
The purpose of this case report is to describe a patient in whom an
osteosarcoma developed at the site of an aneurysmal bone cyst that had been
treated with curettage and bone-grafting six years earlier. The patient was
informed that data concerning the case would be submitted for publication.
Anineteen-year-old man was treated at another hospital in July 1993
because of painful swelling of the right leg of four months' duration.
Radiographs of the tibia made at that time showed a well-defined intracortical
radiolucent lesion in the proximal part of the tibia
(Fig. 1). On physical
examination, the patient had a tender bulging mass measuring 5 × 2
× 2 cm in the proximal part of the right leg. A technetium-99m
whole-body bone scan revealed a focal area of increased uptake of
radioactivity involving the proximal third of the right tibial shaft with some
cold areas in it. No other areas of abnormal uptake of radioactivity were
revealed on the scan. Computed tomography of the right tibia showed a
radiolucent lesion and fluid-fluid level in the cavity. The anterior tibial
cortex was quite thin.
The patient underwent surgery on July 14, 1993. An anterior cortical window
was made to explore the tibial lesion, and a large amount of blood was found
in the cystic cavity. Extensive, meticulous curettage and burring of the
margins of the lesion were performed. Phenol was then applied. The defect was
reconstructed with a strut fibular allograft and autogenous iliac bone graft.
Histological examination of the surgical specimen revealed variously sized
spaces filled with blood with a wall composed of mononuclear stromal cells and
giant cells (Figs. 2-A and
2-B). The pathologic diagnosis
was aneurysmal bone cyst.
No other adjuvant treatment was given, and the surgical wound healed well.
Regular follow-up until 1998 disclosed no clinical or radiographic evidence of
recurrence. In March 1999, the patient noted an enlarging painful mass at the
previous surgical site. Radiographs revealed a recurrent osteolytic lesion in
the tibia. This time, the lesion broke through the anterior cortex of the
tibia with sunburst periosteal reaction and soft-tissue extension
(Fig. 3). The patient was
referred to our institute in May 1999, where an open biopsy was performed.
Histological examination revealed a proliferation of neoplastic osteoblasts
with irregular hyperchromatic nuclei diagnostic of osteosarcoma
(Fig. 4).
The patient received four courses of preoperative chemotherapy, consisting
of intravenous Adriamycin (doxorubicin) and intra-arterial cisplatin, from
June 3, 1999, to August 26, 1999. On September 21, 1999, a wide resection of
the tumor was performed, after which the skeletal defect was reconstructed
with an intercalary allograft and autogenous iliac bone graft and fixed with
an interlocking nail and a buttress plate. A local gastrocnemius flap and
split-thickness skin grafts were used by a plastic surgeon to cover the
soft-tissue defect. The histological examination of the surgical specimen
showed 95% tumor necrosis. The patient was discharged on October 2, 1999, and
he received two more courses of chemotherapy from October 13, 1999, to
November 19, 1999.
Healing of the intercalary allograft to the host bone was noted seven
months after the surgery. At the latest follow-up examination, in October
2003, the patient was alive with no evidence of disease and had excellent
function of the right leg according to the functional rating system of
Enneking et al. (Fig.
5)13.
Note: The authors gratefully acknowledge Hsin-Nung Shih, MD, for
providing the original information on this patient.