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A strange giant cell tumor

2010; Elsevier BV; Volume: 77; Issue: 1 Linguagem: Inglês

10.1016/j.ejrad.2010.06.050

1872-7727

Marco Gambarotti, Maurizio Donato, Marco Alberghini, D. Vanel,

Oral and Maxillofacial Pathology

A 29-year-old male came in 2008 for pain in the knee for 2 months, without swelling. Radiographs (Fig. 1a and b ) and CT (Fig. 1c) revealed an osteolytic lesion of the distal metaphysis of the left femur. A CT-guided biopsy was performed.Histological diagnosis was giant cell tumor (Fig. 1d). The patient underwent a curettage.A diagnosis of giant cell tumor with abundant bone production and histological aggressive features was made. Three months later the patient developed a recurrence, with well limited lytic lesions at the border of the cement, easily detected on CT (Fig. 2a ). After a second CT-guided biopsy an histological diagnosis of recurrence of giant cell tumor of bone was made. However, some features raised the suspicion of malignancy (atypical spindle cells, abundant bone production). For this reason a surgical resection of the distal femur was performed. On the resected specimen there were 2 brownish and soft lesions around the cement, and a third grayish and lardaceous lesion in the distal part of the femur and in the soft tissues around the bone. An histological diagnosis of giant cell-rich osteosarcoma was finally made (Fig. 2b). The patient received adjuvant chemotherapy and is free of disease until now.Fig. 2On CT (a) the recurrence is well visible, as a lytic well limited lesion near the cement (arrow). Histologically (b) on the entire specimen the lesion is more cellular with mononuclear cells showing a more spindle appearance. The production of osteoid is abundant in some areas. These features are consistent with an osteosarcoma. The presence of numerous multinucleated giant cells defined the lesion as a giant cell rich osteosarcoma. (Hematoxiline–Eosin, 10×).View Large Image Figure ViewerDownload Hi-res image Download (PPT)1. DiscussionGiant cell rich-osteosarcoma is a rare entity, whose incidence varies from 0.3% to 13% of all osteosarcomas [1Bathurst N. Sanerkin N. Watt I. Osteoclast-rich osteosarcoma.Br J Radiol. 1986; 59: 667-673Crossref PubMed Scopus (46) Google Scholar, 2Troup J.B. Dahlin D.C. Coventry M.B. The significance of giant cells in osteogenic sarcoma: do they indicate a relationship between osteogenic sarcoma and giant cell tumor of bone.Mayo Clin Proc. 1960; 35: 179-1986Google Scholar, 3Unni K.K. Osteosarcoma.in: Dahlin D.C. Dahlin's bone tumors. Lippincott-Raven, Philadelphia1996: 143-183Google Scholar]. Histologically it consists of a proliferation of atypical stromal cells, with an abundance of osteoclast-like giant cells. Osteoid is usually focally found. It can mimic other giant cell-rich lesions, like giant cell tumor of bone. In particular when a giant cell-rich osteosarcoma with minimal atypia is located in a bone extremity the diagnosis can be extremely difficult [[4]Bertoni F. Bacchini P. Staals E.L. Giant cell-rich osteosarcoma.Orthopedics. 2003; 26: 179-181PubMed Google Scholar].The peak incidence is in the third decade, and it represents a subtype of conventional osteosarcoma. Many osteosarcomas contain osteoclast-like giant cells, which occasionally form clusters, in an otherwise usual osteosarcoma. The term osteoclast-rich osteosarcoma is reserved for those osteosarcomas that contain abundant osteoclast-like giant cells distributed throughout the tumor [[5]Shuhaibar H. Friedman L. Dedifferentiated parostal osteosarcoma with high-grade osteoclast-rich osteogenic sarcoma at presentation.Skeletal Radiol. 1998; 27: 574-577Crossref PubMed Scopus (18) Google Scholar]. At low power view, these lesions show multinucleated giant cells simulating a giant-cell tumor; but on high power cytologic anaplasia of the stromal cells and malignant osteoid production can usually be identified [4Bertoni F. Bacchini P. Staals E.L. Giant cell-rich osteosarcoma.Orthopedics. 2003; 26: 179-181PubMed Google Scholar, 6Mirra J.M. Bone tumors: clinical, radiologic, and pathologic correlations. Lea and Febiger, Philadelphia, PA1989Google Scholar, 7Inwards C. Mcleod R. Bertoni F. Giant cell rich osteosarcoma.Mod Pathol. 1995; 8: 7AGoogle Scholar].The main differential diagnosis is a giant cell tumor, especially when the lesion involves the epiphysis of bones. It is particularly difficult when the stromal cells in the background show slight degree of anaplasia. Fortunately, the vast majority of osteosarcomas are metaphyseal or metadiaphyseal, whereas most giant cell tumors occur in the meta-epiphysis. The peak age of osteosarcoma is in the second decade, and that of giant cell tumor is in the third [[5]Shuhaibar H. Friedman L. Dedifferentiated parostal osteosarcoma with high-grade osteoclast-rich osteogenic sarcoma at presentation.Skeletal Radiol. 1998; 27: 574-577Crossref PubMed Scopus (18) Google Scholar]. Giant cell-rich osteosarcoma can occur in different location from giant-cell tumor: in these cases, even if the differential diagnosis between these tumors on histology is difficult, the location can lead to the correct diagnosis. However, when a giant cell-rich osteosarcoma occurs in a common location for giant-cell tumor, histology is the most important factor in the differential diagnosis, especially the sarcomatous aspect of the stroma. If a giant cell-rich osteosarcoma with minimal atypia is located in the bone extremity the diagnosis is extremely difficult [[4]Bertoni F. Bacchini P. Staals E.L. Giant cell-rich osteosarcoma.Orthopedics. 2003; 26: 179-181PubMed Google Scholar].Also, giant cell-rich osteosarcoma should be differentiated from malignancy in giant cell tumor. The latter consists of a high grade sarcoma arising in a giant cell tumor or at the site of a previously documented giant cell tumor [[8]Fletcher C.D.M. Unni K.K. Mertens F. World Health Organization classification of tumours. Pathology and genetics of tumours of soft tissue and bone. IARC Press, Lyon2002: 313Google Scholar]. In this case the confusion could arise when a primary giant cell tumor with proliferations of round to oval mononuclear cells and multinucleated giant cells coexist with an osteosarcoma, which can be the malignant component. However, there is an abrupt change from the benign giant cell tumor and the malignant component, so areas of benign giant cell tumor are identified, and the malignant component that can cause confusion is a conventional osteosarcoma, which usually does not have abundant giant cells.Thirteen percent of osteosarcomas may show moderate to large numbers of benign osteoclast-like giant cells [[2]Troup J.B. Dahlin D.C. Coventry M.B. The significance of giant cells in osteogenic sarcoma: do they indicate a relationship between osteogenic sarcoma and giant cell tumor of bone.Mayo Clin Proc. 1960; 35: 179-1986Google Scholar]. Therefore, it is useful to widely sample the specimens. Telangiectatic osteosarcoma can have a similar histological picture, especially in more cellular areas, since it is composed of malignant spindle cells with little osteoid production. The difference is made by the detection of cystic blood spaces surrounded by septae containing the sarcomatous cells.It is difficult to correctly assess the characteristics of giant cell-rich osteosarcoma, since its incidence is very low, and only a few previous reports have been made in literature [1Bathurst N. Sanerkin N. Watt I. Osteoclast-rich osteosarcoma.Br J Radiol. 1986; 59: 667-673Crossref PubMed Scopus (46) Google Scholar, 4Bertoni F. Bacchini P. Staals E.L. Giant cell-rich osteosarcoma.Orthopedics. 2003; 26: 179-181PubMed Google Scholar, 9Hong S.J. Kim K.A. Yong H.S. et al.Giant cell-rich osteosarcoma of bone.Eur J Radiol. 2005; 53: 87-90Crossref Scopus (8) Google Scholar, 10Kinochita G. Yasoshima H. Giant cell-rich tumor of the rib.J Orthop Sci. 2006; 11: 312-317Abstract Full Text PDF PubMed Scopus (6) Google Scholar]. Two cases were dedifferentiation in a parostal osteosarcoma [5Shuhaibar H. Friedman L. Dedifferentiated parostal osteosarcoma with high-grade osteoclast-rich osteogenic sarcoma at presentation.Skeletal Radiol. 1998; 27: 574-577Crossref PubMed Scopus (18) Google Scholar, 11Sciot R. Samson I. Dal Cin P. et al.Giant cell rich parosteal osteosarcoma.Histopathology. 1995; 27: 51-55Crossref PubMed Scopus (14) Google Scholar], and one case in the radius was initially diagnosed as a giant cell tumor [[12]Shinozaki T. Fukuda T. Watanabe H. Takagishi K. Giant cell-rich osteosarcoma simulating giant cell tumor of bone.Kitakanto Med J. 2004; 54: 147-151Crossref Scopus (8) Google Scholar]. This and our case demonstrate that a giant cell-rich osteosarcoma with little atypia can simulate a giant cell tumor when it presents in the epiphysis of a long bone.On imaging studies it is also difficult to distinguish giant cell-rich osteosarcoma from giant cell tumors [[13]Nagata S. Nishimura H. Uchida M. Hayabuchi N. Zenmyou M. Harada H. Giant cell-rich osteosarcoma of the distal femur: radiographic and magnetic resonance imaging findings.Radiat Med. 2006; 24: 228-232Crossref PubMed Scopus (8) Google Scholar], but a dense focus of bone on radiograph or CT (as in our case) should raise the suspicion and guide the biopsy on this special location.The diagnosis of giant cell-rich osteosarcoma must be made following strict criteria, since most of the times a lesion with abundance of giant cells can be a conventional osteosarcoma with areas of abundant osteoclast-like giant cells, or a telangiectatic osteosarcoma with focal solid areas. Also, care should be made when diagnosing a lesion as a giant cell tumor, especially if it is in a young patient or in an unusual location.2. ConclusionGiant cell-rich osteosarcoma is a rare subtype of osteosarcoma that should always be kept in mind when examining an osteolytic lesion that resembles a giant cell tumor both radiologically and histologically, especially in young patients or in unusual locations, such as the metaphysis and diaphysis of long bones. The presence of a sclerotic component on imaging examinations, or atypical spindle cells in the stroma between the giant cells is the most useful diagnosis key. The diagnosis of giant cell-rich osteosarcoma should be made only if a conventional osteosarcoma with giant cells, a telangiectatic osteosarcoma with solid areas, and other giant cell-rich lesions have been ruled out. A 29-year-old male came in 2008 for pain in the knee for 2 months, without swelling. Radiographs (Fig. 1a and b ) and CT (Fig. 1c) revealed an osteolytic lesion of the distal metaphysis of the left femur. A CT-guided biopsy was performed. Histological diagnosis was giant cell tumor (Fig. 1d). The patient underwent a curettage. A diagnosis of giant cell tumor with abundant bone production and histological aggressive features was made. Three months later the patient developed a recurrence, with well limited lytic lesions at the border of the cement, easily detected on CT (Fig. 2a ). After a second CT-guided biopsy an histological diagnosis of recurrence of giant cell tumor of bone was made. However, some features raised the suspicion of malignancy (atypical spindle cells, abundant bone production). For this reason a surgical resection of the distal femur was performed. On the resected specimen there were 2 brownish and soft lesions around the cement, and a third grayish and lardaceous lesion in the distal part of the femur and in the soft tissues around the bone. An histological diagnosis of giant cell-rich osteosarcoma was finally made (Fig. 2b). The patient received adjuvant chemotherapy and is free of disease until now. 1. DiscussionGiant cell rich-osteosarcoma is a rare entity, whose incidence varies from 0.3% to 13% of all osteosarcomas [1Bathurst N. Sanerkin N. Watt I. Osteoclast-rich osteosarcoma.Br J Radiol. 1986; 59: 667-673Crossref PubMed Scopus (46) Google Scholar, 2Troup J.B. Dahlin D.C. Coventry M.B. The significance of giant cells in osteogenic sarcoma: do they indicate a relationship between osteogenic sarcoma and giant cell tumor of bone.Mayo Clin Proc. 1960; 35: 179-1986Google Scholar, 3Unni K.K. Osteosarcoma.in: Dahlin D.C. Dahlin's bone tumors. Lippincott-Raven, Philadelphia1996: 143-183Google Scholar]. Histologically it consists of a proliferation of atypical stromal cells, with an abundance of osteoclast-like giant cells. Osteoid is usually focally found. It can mimic other giant cell-rich lesions, like giant cell tumor of bone. In particular when a giant cell-rich osteosarcoma with minimal atypia is located in a bone extremity the diagnosis can be extremely difficult [[4]Bertoni F. Bacchini P. Staals E.L. Giant cell-rich osteosarcoma.Orthopedics. 2003; 26: 179-181PubMed Google Scholar].The peak incidence is in the third decade, and it represents a subtype of conventional osteosarcoma. Many osteosarcomas contain osteoclast-like giant cells, which occasionally form clusters, in an otherwise usual osteosarcoma. The term osteoclast-rich osteosarcoma is reserved for those osteosarcomas that contain abundant osteoclast-like giant cells distributed throughout the tumor [[5]Shuhaibar H. Friedman L. Dedifferentiated parostal osteosarcoma with high-grade osteoclast-rich osteogenic sarcoma at presentation.Skeletal Radiol. 1998; 27: 574-577Crossref PubMed Scopus (18) Google Scholar]. At low power view, these lesions show multinucleated giant cells simulating a giant-cell tumor; but on high power cytologic anaplasia of the stromal cells and malignant osteoid production can usually be identified [4Bertoni F. Bacchini P. Staals E.L. Giant cell-rich osteosarcoma.Orthopedics. 2003; 26: 179-181PubMed Google Scholar, 6Mirra J.M. Bone tumors: clinical, radiologic, and pathologic correlations. Lea and Febiger, Philadelphia, PA1989Google Scholar, 7Inwards C. Mcleod R. Bertoni F. Giant cell rich osteosarcoma.Mod Pathol. 1995; 8: 7AGoogle Scholar].The main differential diagnosis is a giant cell tumor, especially when the lesion involves the epiphysis of bones. It is particularly difficult when the stromal cells in the background show slight degree of anaplasia. Fortunately, the vast majority of osteosarcomas are metaphyseal or metadiaphyseal, whereas most giant cell tumors occur in the meta-epiphysis. The peak age of osteosarcoma is in the second decade, and that of giant cell tumor is in the third [[5]Shuhaibar H. Friedman L. Dedifferentiated parostal osteosarcoma with high-grade osteoclast-rich osteogenic sarcoma at presentation.Skeletal Radiol. 1998; 27: 574-577Crossref PubMed Scopus (18) Google Scholar]. Giant cell-rich osteosarcoma can occur in different location from giant-cell tumor: in these cases, even if the differential diagnosis between these tumors on histology is difficult, the location can lead to the correct diagnosis. However, when a giant cell-rich osteosarcoma occurs in a common location for giant-cell tumor, histology is the most important factor in the differential diagnosis, especially the sarcomatous aspect of the stroma. If a giant cell-rich osteosarcoma with minimal atypia is located in the bone extremity the diagnosis is extremely difficult [[4]Bertoni F. Bacchini P. Staals E.L. Giant cell-rich osteosarcoma.Orthopedics. 2003; 26: 179-181PubMed Google Scholar].Also, giant cell-rich osteosarcoma should be differentiated from malignancy in giant cell tumor. The latter consists of a high grade sarcoma arising in a giant cell tumor or at the site of a previously documented giant cell tumor [[8]Fletcher C.D.M. Unni K.K. Mertens F. World Health Organization classification of tumours. Pathology and genetics of tumours of soft tissue and bone. IARC Press, Lyon2002: 313Google Scholar]. In this case the confusion could arise when a primary giant cell tumor with proliferations of round to oval mononuclear cells and multinucleated giant cells coexist with an osteosarcoma, which can be the malignant component. However, there is an abrupt change from the benign giant cell tumor and the malignant component, so areas of benign giant cell tumor are identified, and the malignant component that can cause confusion is a conventional osteosarcoma, which usually does not have abundant giant cells.Thirteen percent of osteosarcomas may show moderate to large numbers of benign osteoclast-like giant cells [[2]Troup J.B. Dahlin D.C. Coventry M.B. The significance of giant cells in osteogenic sarcoma: do they indicate a relationship between osteogenic sarcoma and giant cell tumor of bone.Mayo Clin Proc. 1960; 35: 179-1986Google Scholar]. Therefore, it is useful to widely sample the specimens. Telangiectatic osteosarcoma can have a similar histological picture, especially in more cellular areas, since it is composed of malignant spindle cells with little osteoid production. The difference is made by the detection of cystic blood spaces surrounded by septae containing the sarcomatous cells.It is difficult to correctly assess the characteristics of giant cell-rich osteosarcoma, since its incidence is very low, and only a few previous reports have been made in literature [1Bathurst N. Sanerkin N. Watt I. Osteoclast-rich osteosarcoma.Br J Radiol. 1986; 59: 667-673Crossref PubMed Scopus (46) Google Scholar, 4Bertoni F. Bacchini P. Staals E.L. Giant cell-rich osteosarcoma.Orthopedics. 2003; 26: 179-181PubMed Google Scholar, 9Hong S.J. Kim K.A. Yong H.S. et al.Giant cell-rich osteosarcoma of bone.Eur J Radiol. 2005; 53: 87-90Crossref Scopus (8) Google Scholar, 10Kinochita G. Yasoshima H. Giant cell-rich tumor of the rib.J Orthop Sci. 2006; 11: 312-317Abstract Full Text PDF PubMed Scopus (6) Google Scholar]. Two cases were dedifferentiation in a parostal osteosarcoma [5Shuhaibar H. Friedman L. Dedifferentiated parostal osteosarcoma with high-grade osteoclast-rich osteogenic sarcoma at presentation.Skeletal Radiol. 1998; 27: 574-577Crossref PubMed Scopus (18) Google Scholar, 11Sciot R. Samson I. Dal Cin P. et al.Giant cell rich parosteal osteosarcoma.Histopathology. 1995; 27: 51-55Crossref PubMed Scopus (14) Google Scholar], and one case in the radius was initially diagnosed as a giant cell tumor [[12]Shinozaki T. Fukuda T. Watanabe H. Takagishi K. Giant cell-rich osteosarcoma simulating giant cell tumor of bone.Kitakanto Med J. 2004; 54: 147-151Crossref Scopus (8) Google Scholar]. This and our case demonstrate that a giant cell-rich osteosarcoma with little atypia can simulate a giant cell tumor when it presents in the epiphysis of a long bone.On imaging studies it is also difficult to distinguish giant cell-rich osteosarcoma from giant cell tumors [[13]Nagata S. Nishimura H. Uchida M. Hayabuchi N. Zenmyou M. Harada H. Giant cell-rich osteosarcoma of the distal femur: radiographic and magnetic resonance imaging findings.Radiat Med. 2006; 24: 228-232Crossref PubMed Scopus (8) Google Scholar], but a dense focus of bone on radiograph or CT (as in our case) should raise the suspicion and guide the biopsy on this special location.The diagnosis of giant cell-rich osteosarcoma must be made following strict criteria, since most of the times a lesion with abundance of giant cells can be a conventional osteosarcoma with areas of abundant osteoclast-like giant cells, or a telangiectatic osteosarcoma with focal solid areas. Also, care should be made when diagnosing a lesion as a giant cell tumor, especially if it is in a young patient or in an unusual location. Giant cell rich-osteosarcoma is a rare entity, whose incidence varies from 0.3% to 13% of all osteosarcomas [1Bathurst N. Sanerkin N. Watt I. Osteoclast-rich osteosarcoma.Br J Radiol. 1986; 59: 667-673Crossref PubMed Scopus (46) Google Scholar, 2Troup J.B. Dahlin D.C. Coventry M.B. The significance of giant cells in osteogenic sarcoma: do they indicate a relationship between osteogenic sarcoma and giant cell tumor of bone.Mayo Clin Proc. 1960; 35: 179-1986Google Scholar, 3Unni K.K. Osteosarcoma.in: Dahlin D.C. Dahlin's bone tumors. Lippincott-Raven, Philadelphia1996: 143-183Google Scholar]. Histologically it consists of a proliferation of atypical stromal cells, with an abundance of osteoclast-like giant cells. Osteoid is usually focally found. It can mimic other giant cell-rich lesions, like giant cell tumor of bone. In particular when a giant cell-rich osteosarcoma with minimal atypia is located in a bone extremity the diagnosis can be extremely difficult [[4]Bertoni F. Bacchini P. Staals E.L. Giant cell-rich osteosarcoma.Orthopedics. 2003; 26: 179-181PubMed Google Scholar]. The peak incidence is in the third decade, and it represents a subtype of conventional osteosarcoma. Many osteosarcomas contain osteoclast-like giant cells, which occasionally form clusters, in an otherwise usual osteosarcoma. The term osteoclast-rich osteosarcoma is reserved for those osteosarcomas that contain abundant osteoclast-like giant cells distributed throughout the tumor [[5]Shuhaibar H. Friedman L. Dedifferentiated parostal osteosarcoma with high-grade osteoclast-rich osteogenic sarcoma at presentation.Skeletal Radiol. 1998; 27: 574-577Crossref PubMed Scopus (18) Google Scholar]. At low power view, these lesions show multinucleated giant cells simulating a giant-cell tumor; but on high power cytologic anaplasia of the stromal cells and malignant osteoid production can usually be identified [4Bertoni F. Bacchini P. Staals E.L. Giant cell-rich osteosarcoma.Orthopedics. 2003; 26: 179-181PubMed Google Scholar, 6Mirra J.M. Bone tumors: clinical, radiologic, and pathologic correlations. Lea and Febiger, Philadelphia, PA1989Google Scholar, 7Inwards C. Mcleod R. Bertoni F. Giant cell rich osteosarcoma.Mod Pathol. 1995; 8: 7AGoogle Scholar]. The main differential diagnosis is a giant cell tumor, especially when the lesion involves the epiphysis of bones. It is particularly difficult when the stromal cells in the background show slight degree of anaplasia. Fortunately, the vast majority of osteosarcomas are metaphyseal or metadiaphyseal, whereas most giant cell tumors occur in the meta-epiphysis. The peak age of osteosarcoma is in the second decade, and that of giant cell tumor is in the third [[5]Shuhaibar H. Friedman L. Dedifferentiated parostal osteosarcoma with high-grade osteoclast-rich osteogenic sarcoma at presentation.Skeletal Radiol. 1998; 27: 574-577Crossref PubMed Scopus (18) Google Scholar]. Giant cell-rich osteosarcoma can occur in different location from giant-cell tumor: in these cases, even if the differential diagnosis between these tumors on histology is difficult, the location can lead to the correct diagnosis. However, when a giant cell-rich osteosarcoma occurs in a common location for giant-cell tumor, histology is the most important factor in the differential diagnosis, especially the sarcomatous aspect of the stroma. If a giant cell-rich osteosarcoma with minimal atypia is located in the bone extremity the diagnosis is extremely difficult [[4]Bertoni F. Bacchini P. Staals E.L. Giant cell-rich osteosarcoma.Orthopedics. 2003; 26: 179-181PubMed Google Scholar]. Also, giant cell-rich osteosarcoma should be differentiated from malignancy in giant cell tumor. The latter consists of a high grade sarcoma arising in a giant cell tumor or at the site of a previously documented giant cell tumor [[8]Fletcher C.D.M. Unni K.K. Mertens F. World Health Organization classification of tumours. Pathology and genetics of tumours of soft tissue and bone. IARC Press, Lyon2002: 313Google Scholar]. In this case the confusion could arise when a primary giant cell tumor with proliferations of round to oval mononuclear cells and multinucleated giant cells coexist with an osteosarcoma, which can be the malignant component. However, there is an abrupt change from the benign giant cell tumor and the malignant component, so areas of benign giant cell tumor are identified, and the malignant component that can cause confusion is a conventional osteosarcoma, which usually does not have abundant giant cells. Thirteen percent of osteosarcomas may show moderate to large numbers of benign osteoclast-like giant cells [[2]Troup J.B. Dahlin D.C. Coventry M.B. The significance of giant cells in osteogenic sarcoma: do they indicate a relationship between osteogenic sarcoma and giant cell tumor of bone.Mayo Clin Proc. 1960; 35: 179-1986Google Scholar]. Therefore, it is useful to widely sample the specimens. Telangiectatic osteosarcoma can have a similar histological picture, especially in more cellular areas, since it is composed of malignant spindle cells with little osteoid production. The difference is made by the detection of cystic blood spaces surrounded by septae containing the sarcomatous cells. It is difficult to correctly assess the characteristics of giant cell-rich osteosarcoma, since its incidence is very low, and only a few previous reports have been made in literature [1Bathurst N. Sanerkin N. Watt I. Osteoclast-rich osteosarcoma.Br J Radiol. 1986; 59: 667-673Crossref PubMed Scopus (46) Google Scholar, 4Bertoni F. Bacchini P. Staals E.L. Giant cell-rich osteosarcoma.Orthopedics. 2003; 26: 179-181PubMed Google Scholar, 9Hong S.J. Kim K.A. Yong H.S. et al.Giant cell-rich osteosarcoma of bone.Eur J Radiol. 2005; 53: 87-90Crossref Scopus (8) Google Scholar, 10Kinochita G. Yasoshima H. Giant cell-rich tumor of the rib.J Orthop Sci. 2006; 11: 312-317Abstract Full Text PDF PubMed Scopus (6) Google Scholar]. Two cases were dedifferentiation in a parostal osteosarcoma [5Shuhaibar H. Friedman L. Dedifferentiated parostal osteosarcoma with high-grade osteoclast-rich osteogenic sarcoma at presentation.Skeletal Radiol. 1998; 27: 574-577Crossref PubMed Scopus (18) Google Scholar, 11Sciot R. Samson I. Dal Cin P. et al.Giant cell rich parosteal osteosarcoma.Histopathology. 1995; 27: 51-55Crossref PubMed Scopus (14) Google Scholar], and one case in the radius was initially diagnosed as a giant cell tumor [[12]Shinozaki T. Fukuda T. Watanabe H. Takagishi K. Giant cell-rich osteosarcoma simulating giant cell tumor of bone.Kitakanto Med J. 2004; 54: 147-151Crossref Scopus (8) Google Scholar]. This and our case demonstrate that a giant cell-rich osteosarcoma with little atypia can simulate a giant cell tumor when it presents in the epiphysis of a long bone. On imaging studies it is also difficult to distinguish giant cell-rich osteosarcoma from giant cell tumors [[13]Nagata S. Nishimura H. Uchida M. Hayabuchi N. Zenmyou M. Harada H. Giant cell-rich osteosarcoma of the distal femur: radiographic and magnetic resonance imaging findings.Radiat Med. 2006; 24: 228-232Crossref PubMed Scopus (8) Google Scholar], but a dense focus of bone on radiograph or CT (as in our case) should raise the suspicion and guide the biopsy on this special location. The diagnosis of giant cell-rich osteosarcoma must be made following strict criteria, since most of the times a lesion with abundance of giant cells can be a conventional osteosarcoma with areas of abundant osteoclast-like giant cells, or a telangiectatic osteosarcoma with focal solid areas. Also, care should be made when diagnosing a lesion as a giant cell tumor, especially if it is in a young patient or in an unusual location. 2. ConclusionGiant cell-rich osteosarcoma is a rare subtype of osteosarcoma that should always be kept in mind when examining an osteolytic lesion that resembles a giant cell tumor both radiologically and histologically, especially in young patients or in unusual locations, such as the metaphysis and diaphysis of long bones. The presence of a sclerotic component on imaging examinations, or atypical spindle cells in the stroma between the giant cells is the most useful diagnosis key. The diagnosis of giant cell-rich osteosarcoma should be made only if a conventional osteosarcoma with giant cells, a telangiectatic osteosarcoma with solid areas, and other giant cell-rich lesions have been ruled out. Giant cell-rich osteosarcoma is a rare subtype of osteosarcoma that should always be kept in mind when examining an osteolytic lesion that resembles a giant cell tumor both radiologically and histologically, especially in young patients or in unusual locations, such as the metaphysis and diaphysis of long bones. The presence of a sclerotic component on imaging examinations, or atypical spindle cells in the stroma between the giant cells is the most useful diagnosis key. The diagnosis of giant cell-rich osteosarcoma should be made only if a conventional osteosarcoma with giant cells, a telangiectatic osteosarcoma with solid areas, and other giant cell-rich lesions have been ruled out.