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Parosteal osteosarcoma mimicking osteochondroma: A radio-histologic approach on two cases

Parosteal osteosarcoma mimicking osteochondroma: A radio-histologic approach on two cases Objective: Parosteal osteosarcoma is a well-differentiated variant of osteosarcoma that affects the surface of the bone. The imaging pattern is very typical. We report two cases mimicking an osteochondroma, radiologically and histologically and propose an explanation. Material: The review of 86 parosteal osteosarcomas of bone revealed this atypical pattern only once. A consultation case was received in the same time, and added to ours. Patients were 28 years old and 56 years old females. Imaging studies included two radiographs, two CTscans, one MRI examination and one bone scan and the results were compared to histology. Results: On imaging, both lesions presented as ossified lobulated masses attached with a broad base to the underlying cortex. No radiolucent cleft separated the masses and the host bone and cortex continuity between the mass and the femur was seen, with medullary communication. The marrow of the mass had a different density and intensity compared to normal marrow. So, there were features of an osteochondroma (cortex and medullary continuity) and of a parosteal osteosarcoma (ossified marrow). Pathological assessment on the final specimen confirmed the presence of low-grade parosteal osteosarcomas, after an erroneous diagnosis of osteochondroma on the initial biopsy. Conclusions: Parosteal osteosarcoma can be rarely confused with osteochondroma. A radiologic-pathologic correlation is essential. Cortex continuity is the most misleading imaging feature that may occur in parosteal osteosarcomas. A knowledge of this misleading pattern will help diagnose the lesion from the beginning. Introduction osteochondroma on imaging studies. Herein, we report Parosteal osteosarcoma (POS) is a slow-growing tumor two cases of POS with sessile configurations arising from which originates from the outer layer of the periosteum the posterior distal femur that simulated osteochondromas and represents 65% of surface osteosarcomas [1] and in radiologically and histologically on the initial biopsy and our database accounts approximately for 4, 8% of all osteo- emphasize on the imaging features that may lead to an sarcomas [2]. Unlike conventional osteosarcomas, it erroneous diagnosis. rd th involves an older age group typically in the 3 and 4 decades of life and shows a slight female predilection Materials and methods [1,3,4]. The most common location of a POS is the poster- The study included two female patients aged 56 and 24 ior aspect of the distal femur accounting for approximately years old respectively. Both patients referred to our twothirdsofall cases[5].Confusion mayrarelyoccur institution for evaluation of a palpable mass located at in differentiating POS from the sessile variant of the postero-lateral aspect of the distal femur. Informa- tion regarding clinical history, physical examination and laboratory tests was recorded. Retrospective evaluation * Correspondence: daniel.vanel@ior.it 1 of the available imaging studies was carried out. Both The Rizzoli Orthopedic Institute, Research Department, Bologna, Italy Full list of author information is available at the end of the article © 2011 Papathanassiou et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Papathanassiou et al. Clinical Sarcoma Research 2011, 1:2 Page 2 of 7 http://www.clinicalsarcomaresearch.com/content/1/1/2 cases were assessed with radiographs (antero-posterior and lateral views) and CT scans before and after con- trast medium i.v. infusion. Additionally, one patient underwent a bone scan and an MRI study which included T1WSE before and after gadolinium adminis- tration and T2W FAT SAT sequences. Imaging results were compared with the initial biopsy findings and final histopathologic diagnosis. Results Both patients presented with focal swelling and mechani- cal blockage of the left knee. The duration of symptoms was 24 and 36 months for each case with no related trauma or infection during this period. Physical examina- tion revealed two hard, immobile tender masses at the postero-lateral aspect of the distal left femur associated with flexion restriction of the joint at 90° degrees. There was no vascular or neurological deficit of the affected limp. The patients did not notice any significant enlarge- ment of the swelling during the period of the symptoms. Routine blood tests were not significant for any patholo- gical findings. Radiographs showed two “exophytic” mineralized masses with a sessile configuration attached to the pos- terior surface of the left distal femur metaphysis (case1: Figure 2 Case 1 - lateral view. Radiographs demonstrate a sessile Figures 1, 2, 3, 4, 5, &6, case 2: Figures 7, 8, 9, 10, & 11; ossified mass arising from the posterior surface of the left distal radiographs: 1-2, 7-8). No radiolucent cleft separated the femur metaphysis. No cleavage plane is observed. masses from the host bone. The lesions maximum dia- meters were 5, 5 cm and 6 cm. Computed tomography demonstrated an intact and continuous femoral cortex the medullar portion of the masses and the femur could encircling the masses. No definite separation between be ascertained and they seemed to communicate. More- over, one lesion (5, 5 cm) had mild involvement of the medullary canal on CT scan. Small unmineralized areas were observed mainly at the periphery of the lesions (Figures 3, & 9). On MR T1W images, one mass (5, 5 cm) had predominantly low SI compared to adjacent muscles and exhibited heterogeneous enhancement post Figure 3 Case 1 - On axial CT scan, the tumor is continuous Figure 1 Case 1 - AP view. within host bone. Nonmineralized areas are located peripherally. Papathanassiou et al. Clinical Sarcoma Research 2011, 1:2 Page 3 of 7 http://www.clinicalsarcomaresearch.com/content/1/1/2 Figure 6 Case 1 - The cartilaginous metaplasia seen in parosteal osteosarcoma can simulate the appearance of an osteochondroma due to the columnar arrangement of chondrocytes and the enchondral ossification (Hematoxiline&Eosine, 10 × magnification). Figure 4 Case 1 - On the gross specimen continuity of the cortex (long arrows), disappearance of the normal cortex (short arrow), and peripheral cartilage (asterisk) are clear. Anastomosing trabecular-appearing bone is surrounded by a moderately cellular spindle cell proliferation. gadolinium administration (Figures 10, & 11). T2W images with fat saturation displayed a heterogeneous lesion containing areas of low to intermediate SI mixed with hyperintense areas, located peripherally. A coexist- ing popliteal cyst was also noticed at the medial aspect of the popliteal fossa. T2 FAT SAT images additionally Figure 5 Case 1 - Spindle cells show mild atypia (Broders grade 2) (Hematoxiline&Eosine, 10 × magnification). Figure 7 Case 2 - AP view. Papathanassiou et al. Clinical Sarcoma Research 2011, 1:2 Page 4 of 7 http://www.clinicalsarcomaresearch.com/content/1/1/2 Figure 10 Case 2 - T1WSE images. documented limited invasion of the medullar canal by the tumor; a finding that was initially suggested on CT scan (Figure 12). The mass was also hot on bone scintigraphy. Both radiographs and CT scans favored the diagnosis of an osteochondroma without excluding the possibility of a low-grade malignancy, like POS. A Figure 8 Case 2 - lateral view: Radiographs exhibit a lobulated ossified mass attached with a broad base to the postero- lateral surface of the left distal femur with no radiolucent cleft. Figure 9 Case 2 - Computed tomography demonstrates an intact and continuous cortex along with communication of the Figure 11 Case 2 - post gadolinium images. The mass has low SI medullary cavities. Limited invasion of the femoral medullar canal on and displays moderate heterogeneous enhancement after is also indicated (black arrow). contrast medium injection. Papathanassiou et al. Clinical Sarcoma Research 2011, 1:2 Page 5 of 7 http://www.clinicalsarcomaresearch.com/content/1/1/2 all benign and malignant neoplasms of bone [6]. Ori- ginally it was described as “benign and malignant par- osteal osteoma” by Geschickter and Copeland in 1951 [7]. Clinically it presents as a hard, immobile swelling with no or slight pain and frequently associated with loss of motion range of the neighboring joint [2,8]. The symptoms are often of prolonged duration [4]. Biologically, the tumor is slow-growing. Pulmonary metastases occur late in the course of the disease, usuallyfollowing oneormorelocal relapses.There- fore, surgical intervention focuses on the local control of the tumor [8]. Early recognition relies upon clinical suspicion and precise radiologic and pathologic evalua- tion. Apart from the posterior aspect of the distal femur, the tumor secondarily affects the proximal humerus followed by the proximal tibia [9]. Diaphyseal involvement is seen in up to 10% of cases [8]. In refer- ence with the classic characteristics of the tumor, both masses were located at the postero-lateral portion of the distal femur and appeared hard, immobile and ten- Figure 12 T2 FAT SAT image shows a heterogeneous lesion der with associated limitation of the knee flexion on containing hyperintense peripheral areas. Medullar invasion is physical examination. evident (white arrow). A coexisting popliteal cyst is also present Macroscopically, POS presents as a dense and well- (asterisk). Proposed drawing of the growth of the tumor, explaining defined ossified mass attached to the underlying cortex the images. [2]. On histologic grounds, the tumor mainly consists of hypocellular fibrous stroma with minimal atypia of spin- low-grade peripheral chondrosarcoma was not consid- dle cells and extensive osteoid in the form of well- ered, the tumor developing inside the marrow. Initial demarcated bony trabeculae, although smaller foci of biopsy results for both lesions suggested an osteochon- cartilage are also encountered [1,2]. A cartilaginous droma. A subsequent surgical biopsy that was per- component is observed in more than 50% of all POSs formed on one of the masses (5, 5 cm) yielded results and in approximately 25% of cases this component lies suggestive of a low grade POS with a cartilaginous com- at the periphery of the tumor. Pathologists and surgeons ponent. Owing to cortex continuity, the differential must recognize this cartilaginous component so as not diagnosis was narrowed between a sessile osteochon- to confuse POS with osteochondroma [4]. droma and a low-grade POS and finally complete mar- Radiographically, POS presents as a densely minera- ginal resections were performed on both cases. lized lobulated mass with irregular margins and Histologic evaluation of the resected specimens con- attached to the subjacent cortex [2,9]. A characteristic firmed parosteal osteosarcomas (grade II) containing finding is a linear radiolucent zone, separating the cartilaginous components (Figure 4, 5, & 6). For one of lesion from the host bone, except for the site of attach- the cases (5, 5 cm), because it was not any longer feasi- ment, called the cleavage plane which represents the ble to perform a wider resection without evoking uncalcified thickened periosteum. However, this radiolu- tumoral spread it was decided to continue with adjuvant cent cleft may be obliterated with advancing tumoral radiation therapy and then closely follow up the patient growth [3,9]. CT scans define accurately the extent of in order to proceed with amputation only in case of the tumor and cortical integrity [8]. MRI images vary in recurrence. The other patient receives a scheduled clini- relation to tumors size as well as the presence of dense cal and imaging follow-up. Both patients continue to osteoid, cartilage, hemorrhage, necrosis or areas of high remain free of disease at the 24-month follow-up. grade tumor or dedifferentiation. MRI is optimal for exhibiting the appropriate biopsy site and potential Discussion medullary invasion prior intervention [8]. Cortex conti- POS is a rare bone-forming malignant surface tumor nuity with some peripheral erosions is a useful diagnosis which carries a much better prognosis than central, key. Conversely, cortex and medullary continuity are high-grade osteosarcoma (approximately 90% of diagnostic features of osteochondroma. Perhaps the dif- patients after 5 years) [2]. It constitutes about 1, 7% of ferent appearances of the medullary cavities of the Papathanassiou et al. Clinical Sarcoma Research 2011, 1:2 Page 6 of 7 http://www.clinicalsarcomaresearch.com/content/1/1/2 lesions compared to the host bone should have raised suspicion. Additionally a high grade osteosarcoma developed inside an osteochondroma is very rare, but possible and has a very similar pattern [10]. A periph- eral cartilaginous cap may be visible on both parosteal osteosarcoma and osteochondroma. A biopsy made at the periphery of the lesion may reinforce the diagnosis of osteochondroma, as in one of our cases. The final correct diagnosis was established after resection, leading to inadequate margins. The disappearance of the clea- vage plane and the preservation of a continuous femoral cortex encircling the tumors are probably attributed to the gradual destruction of the cortex by the slowly growing tumors (Figure 13, 14, 15, & 16). The differential diagnosis of POS may also include other diverse entities such as mature juxtacortical myo- sitis ossificans, parosteal osteoma, fracture callus, Nora’s lesion, periosteal osteosarcoma and/or chondrosarcoma that can be easily distinguished [4,5,11]. In the study of Lin J et al [11], the term “osteochondromalike parosteal Figure 14 The parosteal osteosarcoma at the beginning, with osteosarcomas” was used to describe six surface bone- an almost intact cortex between the tumor and the normal forming malignancies characterized by cortical continu- bone. ity and no evidence of medullary communication or invasion as shown in our cases. In conclusion, osteochondroma is the main counter- osteochondromas, may be atypically seen in POS. part of POS in terms of imaging differential diagnosis. Awareness of these features and thorough radiologic- Cortex continuity and in a lesser degree merge of pathologic correlation is crucial in avoiding erroneous medullary cavities, which are by definition expected in diagnostic considerations and treatment. Figure 13 What an osteochondroma in the same location would look like, with the cortex of the lesion in continuity with the cortex of the femur, normal marrow inside the lesion, and a cartilaginous cuff. Figure 15 One step forward, with invasion of the marrow. Papathanassiou et al. Clinical Sarcoma Research 2011, 1:2 Page 7 of 7 http://www.clinicalsarcomaresearch.com/content/1/1/2 8. Dönmez FY, Tüzün Ü, Başaran C, Tunacĭ M, Bilgiç B, Acunaş G: MRI findings in parosteal Osteosarcoma: correlation with histopathology. Diagn Interv Radiol 2008, 14:147-152. 9. Suresha S, Saifuddin A: Radiological appearances of appendicular osteosarcoma: a comprehensive pictorial review. Clin Radiol 2007, 62:314-323. 10. Vanel D, Picci P, De Paolis M, Mercuri M: Osteosarcoma arising in an exostosis: CT and MRI imaging. AJR 2001, 176:259-260. 11. Lin J, Yao L, Mirra JM, Bahk WJ: Osteochondromalike parosteal osteosarcoma: A report of six cases of anew entity. AJR 1998, 170:1571-77. doi:10.1186/2045-3329-1-2 Cite this article as: Papathanassiou et al.: Parosteal osteosarcoma mimickingosteochondroma: Aradio-histologic approachontwo cases. Clinical Sarcoma Research 2011 1:2. Figure 16 The tumor has eroded and destroyed the cortex, that now looks in continuity with the cortex of the femur. Author details 1 2 The Rizzoli Orthopedic Institute, Research Department, Bologna, Italy. The Rizzoli Orthopedic Institute, Pathology Department, Bologna, Italy. Centre Léon Bérard, Radiology, Lyon, France. The Rizzoli Orthopedic Institute, Orthopedic Surgery Department, Bologna, Italy. San Orsola Hospital, Nuclear Medicine, Bologna, Italy. Authors’ contributions ZP wrote the article. MA and MG reviewed the histology. PT gave the second case, and checked the manuscript. GB checked the accuracy of the surgical part, CT reviewed the manuscript. DV proposed the subject and checked the review of the cases, references and global accuracy. All authors read and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Received: 12 January 2011 Accepted: 25 July 2011 Published: 25 July 2011 References 1. Murphey M, Robbin M, Flemming D, Temple T, Kransdorf M: From the Archives of the AFIP: The Many Faces of Osteosarcoma. Radiographics 1997, 17:1205-1231. 2. Azura M, Vanel D, Alberghini M, Picci P, Staals E, Mercuri M: Parosteal osteosarcoma dedifferentiating into telangiectatic osteosarcoma: importance of lytic changes and fluid cavities at imaging. Skeletal Radiol 2009, 38:685-690. Submit your next manuscript to BioMed Central 3. Jelinek J, Murphey M, Kransdorf M, Shmookler B, Malawer M, Hur R: and take full advantage of: Parosteal Osteosarcoma: Value of MR Imaging and CT in the Prediction of Histologlc Grade. Radiology 1996, 201:837-842. • Convenient online submission 4. Yong-Koo , Nam Ryu Kyung: Parosteal Osteosarcoma of the Scapula. J Korean Med Sci 1999, 14:586-88. • Thorough peer review 5. Subasi M, Kapukaya A, Buyukbayram H, Bilici A: Unusual benign bone • No space constraints or color figure charges lesion simulating parosteal osteosarcoma. J Orthop Sci 2006, 11:529-532. • Immediate publication on acceptance 6. Lindell M, Shirkhoda A, Raymond KA, Murray J, HarIeT : Parosteal Osteosarcoma: Radiologic-Pathologic Correlation with Emphasis on CT. • Inclusion in PubMed, CAS, Scopus and Google Scholar AJR 1987, 148:323-328. • Research which is freely available for redistribution 7. Geschickter CF, Copeland MM: Parosteal osteoma of bone: a new entity. Ann Surg 1951, 133:790-807. Submit your manuscript at www.biomedcentral.com/submit http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Clinical Sarcoma Research Springer Journals

Parosteal osteosarcoma mimicking osteochondroma: A radio-histologic approach on two cases

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Springer Journals
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Copyright © 2011 by Papathanassiou et al; licensee BioMed Central Ltd.
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Biomedicine; Cancer Research; Oncology; Surgical Oncology
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2045-3329
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Abstract

Objective: Parosteal osteosarcoma is a well-differentiated variant of osteosarcoma that affects the surface of the bone. The imaging pattern is very typical. We report two cases mimicking an osteochondroma, radiologically and histologically and propose an explanation. Material: The review of 86 parosteal osteosarcomas of bone revealed this atypical pattern only once. A consultation case was received in the same time, and added to ours. Patients were 28 years old and 56 years old females. Imaging studies included two radiographs, two CTscans, one MRI examination and one bone scan and the results were compared to histology. Results: On imaging, both lesions presented as ossified lobulated masses attached with a broad base to the underlying cortex. No radiolucent cleft separated the masses and the host bone and cortex continuity between the mass and the femur was seen, with medullary communication. The marrow of the mass had a different density and intensity compared to normal marrow. So, there were features of an osteochondroma (cortex and medullary continuity) and of a parosteal osteosarcoma (ossified marrow). Pathological assessment on the final specimen confirmed the presence of low-grade parosteal osteosarcomas, after an erroneous diagnosis of osteochondroma on the initial biopsy. Conclusions: Parosteal osteosarcoma can be rarely confused with osteochondroma. A radiologic-pathologic correlation is essential. Cortex continuity is the most misleading imaging feature that may occur in parosteal osteosarcomas. A knowledge of this misleading pattern will help diagnose the lesion from the beginning. Introduction osteochondroma on imaging studies. Herein, we report Parosteal osteosarcoma (POS) is a slow-growing tumor two cases of POS with sessile configurations arising from which originates from the outer layer of the periosteum the posterior distal femur that simulated osteochondromas and represents 65% of surface osteosarcomas [1] and in radiologically and histologically on the initial biopsy and our database accounts approximately for 4, 8% of all osteo- emphasize on the imaging features that may lead to an sarcomas [2]. Unlike conventional osteosarcomas, it erroneous diagnosis. rd th involves an older age group typically in the 3 and 4 decades of life and shows a slight female predilection Materials and methods [1,3,4]. The most common location of a POS is the poster- The study included two female patients aged 56 and 24 ior aspect of the distal femur accounting for approximately years old respectively. Both patients referred to our twothirdsofall cases[5].Confusion mayrarelyoccur institution for evaluation of a palpable mass located at in differentiating POS from the sessile variant of the postero-lateral aspect of the distal femur. Informa- tion regarding clinical history, physical examination and laboratory tests was recorded. Retrospective evaluation * Correspondence: daniel.vanel@ior.it 1 of the available imaging studies was carried out. Both The Rizzoli Orthopedic Institute, Research Department, Bologna, Italy Full list of author information is available at the end of the article © 2011 Papathanassiou et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Papathanassiou et al. Clinical Sarcoma Research 2011, 1:2 Page 2 of 7 http://www.clinicalsarcomaresearch.com/content/1/1/2 cases were assessed with radiographs (antero-posterior and lateral views) and CT scans before and after con- trast medium i.v. infusion. Additionally, one patient underwent a bone scan and an MRI study which included T1WSE before and after gadolinium adminis- tration and T2W FAT SAT sequences. Imaging results were compared with the initial biopsy findings and final histopathologic diagnosis. Results Both patients presented with focal swelling and mechani- cal blockage of the left knee. The duration of symptoms was 24 and 36 months for each case with no related trauma or infection during this period. Physical examina- tion revealed two hard, immobile tender masses at the postero-lateral aspect of the distal left femur associated with flexion restriction of the joint at 90° degrees. There was no vascular or neurological deficit of the affected limp. The patients did not notice any significant enlarge- ment of the swelling during the period of the symptoms. Routine blood tests were not significant for any patholo- gical findings. Radiographs showed two “exophytic” mineralized masses with a sessile configuration attached to the pos- terior surface of the left distal femur metaphysis (case1: Figure 2 Case 1 - lateral view. Radiographs demonstrate a sessile Figures 1, 2, 3, 4, 5, &6, case 2: Figures 7, 8, 9, 10, & 11; ossified mass arising from the posterior surface of the left distal radiographs: 1-2, 7-8). No radiolucent cleft separated the femur metaphysis. No cleavage plane is observed. masses from the host bone. The lesions maximum dia- meters were 5, 5 cm and 6 cm. Computed tomography demonstrated an intact and continuous femoral cortex the medullar portion of the masses and the femur could encircling the masses. No definite separation between be ascertained and they seemed to communicate. More- over, one lesion (5, 5 cm) had mild involvement of the medullary canal on CT scan. Small unmineralized areas were observed mainly at the periphery of the lesions (Figures 3, & 9). On MR T1W images, one mass (5, 5 cm) had predominantly low SI compared to adjacent muscles and exhibited heterogeneous enhancement post Figure 3 Case 1 - On axial CT scan, the tumor is continuous Figure 1 Case 1 - AP view. within host bone. Nonmineralized areas are located peripherally. Papathanassiou et al. Clinical Sarcoma Research 2011, 1:2 Page 3 of 7 http://www.clinicalsarcomaresearch.com/content/1/1/2 Figure 6 Case 1 - The cartilaginous metaplasia seen in parosteal osteosarcoma can simulate the appearance of an osteochondroma due to the columnar arrangement of chondrocytes and the enchondral ossification (Hematoxiline&Eosine, 10 × magnification). Figure 4 Case 1 - On the gross specimen continuity of the cortex (long arrows), disappearance of the normal cortex (short arrow), and peripheral cartilage (asterisk) are clear. Anastomosing trabecular-appearing bone is surrounded by a moderately cellular spindle cell proliferation. gadolinium administration (Figures 10, & 11). T2W images with fat saturation displayed a heterogeneous lesion containing areas of low to intermediate SI mixed with hyperintense areas, located peripherally. A coexist- ing popliteal cyst was also noticed at the medial aspect of the popliteal fossa. T2 FAT SAT images additionally Figure 5 Case 1 - Spindle cells show mild atypia (Broders grade 2) (Hematoxiline&Eosine, 10 × magnification). Figure 7 Case 2 - AP view. Papathanassiou et al. Clinical Sarcoma Research 2011, 1:2 Page 4 of 7 http://www.clinicalsarcomaresearch.com/content/1/1/2 Figure 10 Case 2 - T1WSE images. documented limited invasion of the medullar canal by the tumor; a finding that was initially suggested on CT scan (Figure 12). The mass was also hot on bone scintigraphy. Both radiographs and CT scans favored the diagnosis of an osteochondroma without excluding the possibility of a low-grade malignancy, like POS. A Figure 8 Case 2 - lateral view: Radiographs exhibit a lobulated ossified mass attached with a broad base to the postero- lateral surface of the left distal femur with no radiolucent cleft. Figure 9 Case 2 - Computed tomography demonstrates an intact and continuous cortex along with communication of the Figure 11 Case 2 - post gadolinium images. The mass has low SI medullary cavities. Limited invasion of the femoral medullar canal on and displays moderate heterogeneous enhancement after is also indicated (black arrow). contrast medium injection. Papathanassiou et al. Clinical Sarcoma Research 2011, 1:2 Page 5 of 7 http://www.clinicalsarcomaresearch.com/content/1/1/2 all benign and malignant neoplasms of bone [6]. Ori- ginally it was described as “benign and malignant par- osteal osteoma” by Geschickter and Copeland in 1951 [7]. Clinically it presents as a hard, immobile swelling with no or slight pain and frequently associated with loss of motion range of the neighboring joint [2,8]. The symptoms are often of prolonged duration [4]. Biologically, the tumor is slow-growing. Pulmonary metastases occur late in the course of the disease, usuallyfollowing oneormorelocal relapses.There- fore, surgical intervention focuses on the local control of the tumor [8]. Early recognition relies upon clinical suspicion and precise radiologic and pathologic evalua- tion. Apart from the posterior aspect of the distal femur, the tumor secondarily affects the proximal humerus followed by the proximal tibia [9]. Diaphyseal involvement is seen in up to 10% of cases [8]. In refer- ence with the classic characteristics of the tumor, both masses were located at the postero-lateral portion of the distal femur and appeared hard, immobile and ten- Figure 12 T2 FAT SAT image shows a heterogeneous lesion der with associated limitation of the knee flexion on containing hyperintense peripheral areas. Medullar invasion is physical examination. evident (white arrow). A coexisting popliteal cyst is also present Macroscopically, POS presents as a dense and well- (asterisk). Proposed drawing of the growth of the tumor, explaining defined ossified mass attached to the underlying cortex the images. [2]. On histologic grounds, the tumor mainly consists of hypocellular fibrous stroma with minimal atypia of spin- low-grade peripheral chondrosarcoma was not consid- dle cells and extensive osteoid in the form of well- ered, the tumor developing inside the marrow. Initial demarcated bony trabeculae, although smaller foci of biopsy results for both lesions suggested an osteochon- cartilage are also encountered [1,2]. A cartilaginous droma. A subsequent surgical biopsy that was per- component is observed in more than 50% of all POSs formed on one of the masses (5, 5 cm) yielded results and in approximately 25% of cases this component lies suggestive of a low grade POS with a cartilaginous com- at the periphery of the tumor. Pathologists and surgeons ponent. Owing to cortex continuity, the differential must recognize this cartilaginous component so as not diagnosis was narrowed between a sessile osteochon- to confuse POS with osteochondroma [4]. droma and a low-grade POS and finally complete mar- Radiographically, POS presents as a densely minera- ginal resections were performed on both cases. lized lobulated mass with irregular margins and Histologic evaluation of the resected specimens con- attached to the subjacent cortex [2,9]. A characteristic firmed parosteal osteosarcomas (grade II) containing finding is a linear radiolucent zone, separating the cartilaginous components (Figure 4, 5, & 6). For one of lesion from the host bone, except for the site of attach- the cases (5, 5 cm), because it was not any longer feasi- ment, called the cleavage plane which represents the ble to perform a wider resection without evoking uncalcified thickened periosteum. However, this radiolu- tumoral spread it was decided to continue with adjuvant cent cleft may be obliterated with advancing tumoral radiation therapy and then closely follow up the patient growth [3,9]. CT scans define accurately the extent of in order to proceed with amputation only in case of the tumor and cortical integrity [8]. MRI images vary in recurrence. The other patient receives a scheduled clini- relation to tumors size as well as the presence of dense cal and imaging follow-up. Both patients continue to osteoid, cartilage, hemorrhage, necrosis or areas of high remain free of disease at the 24-month follow-up. grade tumor or dedifferentiation. MRI is optimal for exhibiting the appropriate biopsy site and potential Discussion medullary invasion prior intervention [8]. Cortex conti- POS is a rare bone-forming malignant surface tumor nuity with some peripheral erosions is a useful diagnosis which carries a much better prognosis than central, key. Conversely, cortex and medullary continuity are high-grade osteosarcoma (approximately 90% of diagnostic features of osteochondroma. Perhaps the dif- patients after 5 years) [2]. It constitutes about 1, 7% of ferent appearances of the medullary cavities of the Papathanassiou et al. Clinical Sarcoma Research 2011, 1:2 Page 6 of 7 http://www.clinicalsarcomaresearch.com/content/1/1/2 lesions compared to the host bone should have raised suspicion. Additionally a high grade osteosarcoma developed inside an osteochondroma is very rare, but possible and has a very similar pattern [10]. A periph- eral cartilaginous cap may be visible on both parosteal osteosarcoma and osteochondroma. A biopsy made at the periphery of the lesion may reinforce the diagnosis of osteochondroma, as in one of our cases. The final correct diagnosis was established after resection, leading to inadequate margins. The disappearance of the clea- vage plane and the preservation of a continuous femoral cortex encircling the tumors are probably attributed to the gradual destruction of the cortex by the slowly growing tumors (Figure 13, 14, 15, & 16). The differential diagnosis of POS may also include other diverse entities such as mature juxtacortical myo- sitis ossificans, parosteal osteoma, fracture callus, Nora’s lesion, periosteal osteosarcoma and/or chondrosarcoma that can be easily distinguished [4,5,11]. In the study of Lin J et al [11], the term “osteochondromalike parosteal Figure 14 The parosteal osteosarcoma at the beginning, with osteosarcomas” was used to describe six surface bone- an almost intact cortex between the tumor and the normal forming malignancies characterized by cortical continu- bone. ity and no evidence of medullary communication or invasion as shown in our cases. In conclusion, osteochondroma is the main counter- osteochondromas, may be atypically seen in POS. part of POS in terms of imaging differential diagnosis. Awareness of these features and thorough radiologic- Cortex continuity and in a lesser degree merge of pathologic correlation is crucial in avoiding erroneous medullary cavities, which are by definition expected in diagnostic considerations and treatment. Figure 13 What an osteochondroma in the same location would look like, with the cortex of the lesion in continuity with the cortex of the femur, normal marrow inside the lesion, and a cartilaginous cuff. Figure 15 One step forward, with invasion of the marrow. Papathanassiou et al. Clinical Sarcoma Research 2011, 1:2 Page 7 of 7 http://www.clinicalsarcomaresearch.com/content/1/1/2 8. Dönmez FY, Tüzün Ü, Başaran C, Tunacĭ M, Bilgiç B, Acunaş G: MRI findings in parosteal Osteosarcoma: correlation with histopathology. Diagn Interv Radiol 2008, 14:147-152. 9. Suresha S, Saifuddin A: Radiological appearances of appendicular osteosarcoma: a comprehensive pictorial review. Clin Radiol 2007, 62:314-323. 10. Vanel D, Picci P, De Paolis M, Mercuri M: Osteosarcoma arising in an exostosis: CT and MRI imaging. AJR 2001, 176:259-260. 11. Lin J, Yao L, Mirra JM, Bahk WJ: Osteochondromalike parosteal osteosarcoma: A report of six cases of anew entity. AJR 1998, 170:1571-77. doi:10.1186/2045-3329-1-2 Cite this article as: Papathanassiou et al.: Parosteal osteosarcoma mimickingosteochondroma: Aradio-histologic approachontwo cases. Clinical Sarcoma Research 2011 1:2. Figure 16 The tumor has eroded and destroyed the cortex, that now looks in continuity with the cortex of the femur. Author details 1 2 The Rizzoli Orthopedic Institute, Research Department, Bologna, Italy. The Rizzoli Orthopedic Institute, Pathology Department, Bologna, Italy. Centre Léon Bérard, Radiology, Lyon, France. The Rizzoli Orthopedic Institute, Orthopedic Surgery Department, Bologna, Italy. San Orsola Hospital, Nuclear Medicine, Bologna, Italy. Authors’ contributions ZP wrote the article. MA and MG reviewed the histology. PT gave the second case, and checked the manuscript. GB checked the accuracy of the surgical part, CT reviewed the manuscript. DV proposed the subject and checked the review of the cases, references and global accuracy. All authors read and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Received: 12 January 2011 Accepted: 25 July 2011 Published: 25 July 2011 References 1. Murphey M, Robbin M, Flemming D, Temple T, Kransdorf M: From the Archives of the AFIP: The Many Faces of Osteosarcoma. Radiographics 1997, 17:1205-1231. 2. Azura M, Vanel D, Alberghini M, Picci P, Staals E, Mercuri M: Parosteal osteosarcoma dedifferentiating into telangiectatic osteosarcoma: importance of lytic changes and fluid cavities at imaging. Skeletal Radiol 2009, 38:685-690. Submit your next manuscript to BioMed Central 3. Jelinek J, Murphey M, Kransdorf M, Shmookler B, Malawer M, Hur R: and take full advantage of: Parosteal Osteosarcoma: Value of MR Imaging and CT in the Prediction of Histologlc Grade. Radiology 1996, 201:837-842. • Convenient online submission 4. Yong-Koo , Nam Ryu Kyung: Parosteal Osteosarcoma of the Scapula. J Korean Med Sci 1999, 14:586-88. • Thorough peer review 5. Subasi M, Kapukaya A, Buyukbayram H, Bilici A: Unusual benign bone • No space constraints or color figure charges lesion simulating parosteal osteosarcoma. J Orthop Sci 2006, 11:529-532. • Immediate publication on acceptance 6. Lindell M, Shirkhoda A, Raymond KA, Murray J, HarIeT : Parosteal Osteosarcoma: Radiologic-Pathologic Correlation with Emphasis on CT. • Inclusion in PubMed, CAS, Scopus and Google Scholar AJR 1987, 148:323-328. • Research which is freely available for redistribution 7. Geschickter CF, Copeland MM: Parosteal osteoma of bone: a new entity. Ann Surg 1951, 133:790-807. Submit your manuscript at www.biomedcentral.com/submit

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Clinical Sarcoma Research – Springer Journals

Published: Jul 25, 2011

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