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Turk J Med Sci2007; 37 (4): 243-249 TBTAKE-mail: medsci@tubitak.gov.tr

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CASE REPORT

Sacral Chondroblastic Osteosarcoma Misdiagnosed asChondrosarcoma and Chordoma

Abstract: Chondroblastic osteosarcoma (COS), a subgroup of intramedullary osteosarcoma, is usually locatedin the knee region of the body. It is most common in adolescents and early adulthood. COS has similar clinicaland radiological features to those of conventional osteosarcomas.

A 17-year-old male suffered from walking problems and lower limb pain. CT and MRI revealed a mass withsoft tissue density and bone destruction at the level of L5-S1. It was described as posttraumatic hematoma.In cytopathologic examination, initial diagnosis was chordoma in fine-needle aspiration cytology (FNAC),chondrosarcoma in incisional biopsy, and finally COS in total resection specimen.

Because sacral location of COS is very rare, this report aimed to discuss radiological and pathological diagnosticpitfalls of COS in light of the literature.

Key Words: Chondroblastic osteosarcoma, chondrosarcoma, chordoma, sacrum

Kondrosarkom ve Kordoma ile Karfltrlan Sakral Kondroblastik Osteosarkom

zet: Kondroblastik osteosarkoma(COS), intramedller osteosarkomun bir alt grubudur ve genelde dizblgesinde yerleflir. Ergenlik anda sktr. COSun klinik ve radyolojik bulgular dier osteosarkomlara benzer.

Yrme problemleri ve alt ekstremitede ar yaknmas olan 17 yaflnda bir hastann tomografi ve MRincelemelerinde L5-S1 dzeyinde yumuflak doku dansitesinde ve kemikte destrksiyona yol aan kitle saptand.Kitle posttravmatik hematom olarak rapor edildi. nce ine aspirasyon biyopsisi(FNAC) kordoma, insizyonelbiyopsisi kondrosarkoma olarak rapor edildi ve sonuta COS total olarak karld.

Anahtar Szckler: Konroblastik Osteosarkom, Kondrosarkom, kordoma, Sakrum

Nusret AKPOLAT1

Hanefi YILDIRIM2

Krflat POYRAZ2

1 Department of Pathology, Faculty of Medicine, Frat University, Elaz - TURKEY

2 Department of Radiology, Faculty of Medicine, Frat University, Elaz - TURKEY

Received: October 09, 2006Accepted: June 26, 2007

Correspondence

Nusret AKPOLATDepartment of Pathology,

Faculty of Medicine, Frat University,

23119 Elaz - Turkey

nakpolat@firat.edu.tr

Introduction

Chondroblastic osteosarcoma (COS) is a subgroup of intramedullary osteosarcoma,and primarily involves the femur and tibia. It is most common in adolescents and in earlyadulthood and constitutes 9-25% of osteosarcomas. COSs show similar clinical andradiological features to those of conventional osteosarcomas. Morphologically, they arecharacterized with chondroid and osteoid differentiation (1-3).

Chondrosarcoma (CS) is the third most frequent bone tumor (20-30%) followingmyelomas and osteosarcomas, respectively. They mostly occur in elderly patients with apeak incidence in the sixth decade. Shoulder, pelvis, proximal femur and costalinvolvement are frequently seen, but sacral involvement is very rare (2%) (4).

Chondroid chordomas (CC) are rare malignant tumors that are frequently located inthe sphenooccipital region and predominantly seen in early adulthood and males. Theyarise from embryological notochord remnants. They are considered a subgroup of classicchordomas because of their clinical and pathological differences from classic chordomas(5-8).

These three neoplasms show chondroid differentiation. Therefore, in small biopsyspecimens, differential diagnosis is difficult. Morphologically accurate diagnosis ismandatory because of different treatment and clinical features of these three malignantneoplasms. In this report, problems and solutions related to these three differententities are discussed.

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AKPOLAT, N et al. Sacral Chondroblastic Osteosarcoma Turk J Med Sci

Case Report

A 17-year-old male patient with walking problemsand complaints of lower limb pain was admitted to theNeurosurgery Department of Firat University, FiratMedical Center. Computed tomography (CT) showed amass lesion with soft tissue density and bone destructionat the level of L5-S1, indicating a posttraumatichematoma. Magnetic resonance imaging (MRI) findingsincluded an enhancing inflammatory soft tissue mass thatcompressed on the nerve roots at the level of L5-S2 withbone destruction. The mass was extending into the spinalcanal and involved S1 and S2 vertebral bodies (Figure 1).

In CT-guided fine-needle aspiration cytology (FNAC)of this lesion, small multinucleolar, pleomorphic,transparent malignant tumoral cells with oval-roundnucleus or fusiform large nucleus in myxomatousbackground were observed (Figure 2).Immunohistochemical staining for S-100 (Lab VisionCorporation, CA, USA) and vimentin (Lab VisionCorporation, CA, USA) were positive. In FNAC, chordomawas diagnosed.

In microscopic examination of the biopsy specimen,lobulated chondroid areas and neoplastic cells were seenin myxoid background. In cartilaginous areas, there were

Figure 1. MRI shows soft tissue lesion inflicting vertebral destructionin the presacral region (L5-S2).

Figure 2. FNAC: Neoplastic cells show nuclear membrane irregularity, coarse chromatin, pleomorphismand hyperchromasia (MGG, x1000).

neoplastic chondrocytes, some with large nucleus andcoarse chromatin and some with one or more nucleolusand irregular-edged fine chromatin within lacunae whichwere surrounded by hyaline matrix. Cytoplasms of theneoplastic chondrocytes were narrow with clear

perinuclear halo (Figure 3). Malignant cells were presentwith evident pleomorphism and hyperchromatic nucleusand without a characteristic pattern within large myxoidareas around chondroid areas (Figure 4). Based on thesefindings, the diagnosis was CS (grade I-II).

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Vol: 37 No: 4 Sacral Chondroblastic Osteosarcoma August 2007

Figure 3. Malignant chondroid cells and coagulation necrosis (H&E, x400).

Figure 4. Malignant mesenchymal cells with hyperchromatic and pleomorphic nuclei in myxoidbackground (H&E, x200).

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AKPOLAT, N et al. Sacral Chondroblastic Osteosarcoma Turk J Med Sci

The tumor was totally resected. The specimenconsisted of two pieces (8x6x3 cm and 7x5x2 cm) thatcontained bone and soft tissue components. Inmicroscopic examination, there were lobulated malignantchondroid areas and oval-spindle shaped malignant cellsin myxoid background. Osteoid formation was locatedbetween spindle malignant cells. Enchondral ossificationwas shown in chondroid areas. The tumor was diagnosedas grade III COS.

In immunohistochemical stain, neoplastic cells werepositive for cytokeratin (Lab Vision Corporation, CA,USA), epithelial membrane antigen (EMA) (Lab VisionCorporation, CA, USA) and S-100 (Lab VisionCorporation, CA, USA). For this reason, initial biopsyspecimens were reassessed. Serial cutting was done ofthe small biopsy material and the material on the slidewas larger than of the first slides. There were smallosteoid focuses (Figure 5) and large enchondralossification areas. It was concluded that the first biopsyhad been misdiagnosed as CS.

The patient received radiotherapy. No local recurrenceor metastasis was detected in the postoperative 25thmonth.

Discussion

CSs are the third most frequent bone tumors with apredilection for male gender. Peak incidence is in the sixthdecade. The shoulder, pelvis, proximal femur, and costaeare the most frequent sites of involvement. Sacralinvolvement (2%) is highly rare (4).

Conventional CSs may be hyalinized, myxoid or mixed.Hyaline CSs are characterized with hypercellular hyalinecartilage with atypical chondrocytes within lacunae.Conversely, in myxoid CSs, atypical chondrocytes are notseen in the lacunae and constitute large neoplastic cellgroups in myxoid matrix. Neoplastic cells areimmunohistochemically positive for vimentin and S-100and negative for epithelial markers such as keratin andEMA in CSs. Generally, typical CS diagnosis can be basedon these findings, but myxoid variant can be confusedwith chordoma (4,6).

Chordomas have three subtypes: classical,dedifferentiated, and chondroid. Unlike conventionalchordoma, CC involves the sphenooccipital region, and itis more frequent in early adulthood with a betterprognosis (5,6). Conventional chordomas include largeepithelioid cell cords within vesicular myxoid stroma and

Figure 5. Osteoid production (H&E, x400).

solid nests. Chondroid variant differs from typicalchordoma with its hyalinized stroma and might beconfused with CS. Differential diagnosis of CS and CC isdifficult (7,8). In myxoid CS, neoplastic chondrocytes arerelatively small and narrow. They do not show nestformation. Conversely, chordoma cells are larger andhave dense eosinophilic cytoplasms. They form groups,and desmosomes can be seen between cells.Immunohistochemical staining is very important indifferential diagnosis of these two tumors. Chordomasare immunohistochemically positive for vimentin, S-100,EMA and cytokeratin (9,10).

Clinical behavior, recurrence, and metastaticcharacteristics of CS and CC are very different.Therefore, differential diagnosis based on pathologicalevaluation is necessary. Theoretically, it is possible todifferentiate CC from classic CS with morphology, but inpractice, it is difficult. Thus, false diagnosis is possible. Ina study with 200 skull base CS, 34% of the cases werediagnosed as chordoma initially; however, furthermorphologic and immunohistochemical assessmentsshowed that these were actually CS (6).

COS and conventional osteosarcoma have similarclinical, radiological, and prognostic features. COSsconstitute 9-25% of conventional osteosarcomas (2).COS can be confused with CS in small biopsy specimens,and differential diagnosis can be difficult.