Osteosarcoma is a rare tumour of bone the etiology of which is poorly understood, but it may arise from benign lesions. Malignant transformation in hemangiomas, in the absence of prior radiation, is exceedingly rare and the resulting neoplasm is usually an angiosarcoma. We report the case of a 30-year-old woman where investigation for thigh pain revealed a distal femoral hemangioma. She represented with pain and mass 18 years later, leading to a confirmed diagnosis of osteosarcoma at the same site.
Osteosarcomas may arise from a variety of benign lesions. In this article we report the case of a histologically confirmed hemangioma which subsequently underwent malignant change into an osteosarcoma.
An initial core needle biopsy was non-diagnostic and a large open trephine biopsy was therefore performed. The sections showed dense sclerotic bone lesion exhibiting remodelling of lamellar bone trabeculae. This was associated with prominent activity of both osteoblasts and osteoclasts, but no osteoblastic cytological atypia was seen. The intertrabecular tissue showed a proliferation of crowded thinwalled blood vessels lined by flat endothelial cells, again lacking atypia, and associated with interspersed erythrocytes. The features were those of an intraosseous hemangioma (Figure 1A,E). There was no evidence of malignancy. The slides were reviewed by 2 experienced pathologists who concurred with this interpretation.
Seventeen years later, the patient re-presented with an enlarging painful mass of the left knee that was associated with dysesthesia at the anterior aspect of the left leg and foot. Physical examination was otherwise normal. The patient was otherwise healthy, took simple analgesics for shoulder pain and no other medication.
The repeat x-ray demonstrated an aggressive process, featuring poorly marginated area of sclerosis/lysis occupying the lateral femoral condyle with cortical destruction laterally and ill-defined calcification in the adjacent soft tissues (Figure 2). CT confirmed a lytic/sclerotic bony lesion with cortical perforation, periosteal reaction and calcified matrix (Figure 3). MRI further affirmed the aggressive nature of lesion that showed a soft tissue component seen extending through the breached cortex into the adjacent muscle, with surrounding edema (Figure 4). The lesion measured 6.6 x 5.1 x 5.3 cm and showed hypointensity on T1W images and heterogeneous hyperintensity on T2W images. The lesion was again positive on bone scan but with no evidence of bone metastases. Diagnoses of osteosarcoma, chondrosarcoma and calcified metastases from a mucinous tumour were considered.
A CT-guided core biopsy was performed using an 11G coaxial needle and a 14G biopsy needle via a lateral approach. The histology sections demonstrated trabeculae of lamellar bone permeated by a high-grade malignant spindle and polygonal cell neoplasm. This was associated with production of osteoid matrix and irregular woven bone trabeculae, characteristic of an osteosarcoma (Figure 5A-D). No residual hemangioma was identified.
Associations have also been made with tall stature, pubertal hormones, acromegaly, viruses and various cancer predisposition syndromes including retinoblastoma[3].
Osteosarcomas have been reported to arise from heterotopic bone secondary to dermatomyositis and thermal injury, giant cell tumors (GCT), irradiated aneurysmal bone cysts (ABC), osteoblastomas, solitary osteochondromas and fibrous dysplasia[4-9]. Malignant change in GCTs is most commonly reported after radiation, but can be spontaneous and has even occurred in a GCT lung metastasis[6].
Difficulty in histological diagnosis of osteosarcoma has been reported when the differential includes other osteoid producing tumours, but distinction from hemangioma is usually simple. Bertoni et al. described 17 cases of osteosarcoma that resembled osteoblastoma on histological analysis[10]. In the present case, the original histological appearances were distinctly different from osteosarcoma and the diagnosis of hemangioma was confirmed by 3 pathologists on the basis of a large open trephine biopsy. Furthermore, the time interval was sufficiently long to exclude a misdiagnosed indolent osteosarcoma due to a sampling error.
Osteosarcoma is the most common primary sarcoma of bone, but remains rare (estimated 1-2 cases per million/ population/year for 25-59 age group)[3]. The possibility of a coincidental osteosarcoma arising at the site of a hemangioma is statistically unlikely in the absence of other known predisposing factors, but has to be considered. The increased rate of bone turnover induced by the hemangioma could have acted as a substrate for the development of a secondary malignancy in a similar mechanism to the development of osteosarcoma in Paget's disease.
The period of time taken for the malignant transformation was 18 years. Previous reports of malignant transformation to osteosarcoma in the literature cover a wide range of timescales including 28 years for a case of dermatomyositis case[5], 6 years for a GCT[69 and 7 years for an ABC[7]. Obana reported that the time taken for a hemangioma to undergo malignant change to angiosarcoma as 2 years[2]. Our case falls within this very wide spectrum.
In conclusion we present the unique case of an osteosarcoma arising from a hemangioma 18 years after original diagnosis.
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