A peculiar location of a rare bone tumor: sternal lipoma

A peculiar location of a rare bone tumor: sternal lipoma Poster No.: P-0033 Congress: ESSR 2016 Type: Authors: Keywords: DOI: Scientific Poster Z. Akkaya, C. Uzun, S. Enon, G. Kocaman, G. Sahin; Ankara/TR MR, CT, Musculoskeletal system, Musculoskeletal bone, Bones, Diagnostic procedure, Neoplasia 10.1594/essr2016/P-0033 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. www.essr.org Page 1 of 10

Purpose is to present the CT and MRI findings of a case of lipoma of the sternum, which is the notorious bone for malignant lesions and review the relevant literature on sternal tumors and intraosseous lipomas for differential diagnosis. Methods and Materials A 68 year- old male patient was referred to our department for further evaluation of a sternal mass, which was incidentally noticed on a chest CT that was performed for refractory cough and back pain. The patient did not complain of any sternal or retrosternal pain, denied any recent swelling at the anterior chest wall or any known history of prior trauma. Although a very thorough clinical work up was performed, including a diagnostic bronchoscopy and a whole body PET-CT, no primary site of malignancy could be detected. Following thorax CT, he underwent contrast-enhanced (0.1 mmol/kg gadoversetamid ) 3.0 T MR imaging of anterior chest wall. Results Thorax CT revealed a heterogenous mass in manubrium sterni without any soft tissue counterpart or cortical destruction. Areas of curvilinear- amorphous calcifications centrally, within the lesion were noted as well as low density foci (Fig. 1 on page 3), however, there was no periosteal reaction or permeative bone changes. Sagittal multiplanar reformatted (MPR) and volume rendered (VR) images of bone and soft tissue windows depict the expansile nature of the mass without a destructive pattern (Fig. 2 on page 3). On MRI, the high T1 and T2 signal changes within the lesion (Fig. 3 on page 4) and homogenous suppression of these areas with fat suppression techniques confirmed the lipomatous nature of the mass (Fig. 4 on page 5). Page 2 of 10

Intralesional calcifications were also noted as signal void, curvilinear areas in line with the CT findings (Fig. 3 on page 4). Contrast enhanced fat-suppressed T1-weighted images depict no apparent enhancing separate component and the fatty nature of the tumor is pronounced even more with significantly more fat suppression within the lesion compared to the surrounding areas of fatty bone marrow (Fig. 4 on page 5). As a bone biopsy would have been very invasive, radiological follow up was planned and the control MRI at the end of almost one year showed no remarkable difference in the findings (Fig. 5 on page 6). Images for this section: Fig. 1: Axial chest CT images with bone(a) and soft tissue (b) window-level settings show the expansile sternal mass with central amorphous areas of calcification (red arrow) and foci of low density areas (blue arrow). At closer look, a CT density of -18 HU was measured at one of these low density foci (c). Page 3 of 10

Fig. 2: Sagittal reformatted images with bone (a) and soft tissue (b)window-level settings of the sternal mass depict the expansion of manibrium sterni, however, note that the cortical bone is intact and periosteal reaction or soft tissue component are not present. Also body and xyphoid process of sternum are spared. VR images of anterior chest wall at the sternocostal- sternoclavicular junctions (c) and coronal (d) and sagittal (e) views of sternum at narrower window level setting depict the central calcifications sorrounded by areas of low density (arrows) and bony expansion. Page 4 of 10

Fig. 3: Coronal T1- weighted (a) and sagittal T2 -weighted (b) images of manubrium sterni confirm the expansile changes and show relatively high signal intensity at manubrium sterni compared to the surrounding fatty marrow areas or proximal sternal body (red arrow). The calcifications appear as signal void areas (blue arrows) on both T1 and T2- weighted images Fig. 4: Contrast enhanced, fat suppressed coronal T1- weighted image (a) and coronal STIR image (b) depict the homogenous fat suppression within the lesion. No apparent enhancing component is seen. Note the relatively more hypointense appearance of the Page 5 of 10

lesion adjacent to the normal fatty marrow (red arrows) and manubrium sterni on the STIR image (blue arrow). Fig. 5: Axial T1- weighted (a), fat-suppressed contrast enhanced T1- weighted images depict the fatty nature of the lesion with central calcifications and no apparent enahncing component. Axial T1- weighted image from the follow up MRI of the patient 11 months later (c) shows no significant change within the lesion. Page 6 of 10

Conclusion Primary bone tumors of the chest wall are uncommon, accounting for 5-8% of all skeletal masses (1). Sternal masses which account for less than 5% of all chest wall bone tumors are usually malignant and it is a rule of thumb to exclude a malignant lesion in any case of bone tumor involving sternum (2-4). Metastatic lesions at sternum are far more frequent than primary sternal lesions and among the most common primary sources, breast, lung, thyroid, kidney, colon and lymphomas can be listed (3,4). Any new sternal mass in a patient with history of a malignancy should be considered a metastasis until proven otherwise. Primary tumors are relatively uncommon at sternum, however when present they are much more frequently malignant than benign (3). For adults most common primary malignancy of sternum is chondrosarcoma, followed by myeloma, lymphoma, osteosarcoma. Patients with chondrosarcoma, which occurs most frequently in 4th-6th decades of life at this location, usually present with painless mass. The typical ring-and-arc or stippled mineralization pattern, which is best appreciated at CT, is a reliable diagnostic clue (2,4). On MRI chondrosarcomas have high signal intensity at T2 weighted images due to the chondroid matrix and show peripheral-septal enhancement pattern (2). Plasmocytoma which is produced by localized proliferations of plasma cells with various degree of differentiation, or its diffuse form, namely, multiple myeloma may both involve sternum, especially during the 6th or 7th decades of life. Clinically, pain, weakness and weight loss are common symptoms and radiologically, bone destruction with discrete "punched-out" margins is seen. At CT, lytic nature, lack of intrinsic calcifications and expansile changes can be better appreciated. At MRI, plasmocytomas have hypointense signal at T1 weighted images and hyperintense signal at T2 weighted images (4). Osteosarcomas of sternum are more commonly seen at a relatively older age compared to osteosarcomas of the extremities (median age, 42 years) and they are usually secondary lesions in previously irradiated bone (5). Clinically osteosarcomas manifest as a painful swelling and radiologically, a mass lesion which contains bone and soft tissue and shows areas of osteolytic change, calcifications and osteoid matrix which tend to be centrally located. At MRI predominantly high signal intensity on T2-weighted images and heterogenous enhancement pattern on postcontrast images are seen. Ewing sarcoma, which is the most common primary bone tumor of sternum in children, also manifests as a painful mass (2,4). At CT, a permeative, lytic, expansile lesion with soft tissue component and cortical and medullary destruction is seen. At MRI, the tumor Page 7 of 10

exhibits heterogenous high signal intensity on both T1 and T2- weighted images due to hemorrhage and necrosis. The spectrum of benign lesions of sternum, which are quite rare, include enchondroma, osteochondroma, hemangioma, hemangiopericytoma, enostosis, osteoid osteoma, fibrous dysplasia, Paget's disease, Langerhans cell histiocytosis, aneurysmal bone cyst, eosinophilic granuloma, giant cell tumor, brown tumor, nonossifying fibroma and chondromyxoid fibroma (4). Intraosseous lipoma, which has a reported incidence of 0.1% of all bone tumors, is the most common lipogenic tumor of the bone (6,7). In the appendicular skeleton, common locations include calcaneus, intertrochanteric region of femur and long bones such as tibia, fibula, humerus and radius. In the axial skeleton, intraosseous lipomas have been reported in skull, mandible, spine, sacrum, pelvic bones (especially ilium near the sacroiliac joints) and ribs (7-9). However, sternum is a very atypical location. In the long bones they are usually intramedullary and in the metaphyseal or diaphyseal regions. The patients' ages may vary vastly but intraosseous lipomas most commonly present in the 4th- 5th decades. Unlike soft tissue lipomas, males are slightly more affected. Clinically they may be asymptomatic or associated with pain (7,8). Histopathologically Milgram divided intraosseous lipomas into three stages which also correspond to their radiologic appearances. In stage 1, lesions contain viable fat without necrosis and cause trabecular resorption. In stage 2 lesions demonstrate viable fat and fat necrosis, as well as regions of dystrophic calcification. Stage 3 lesions demonstrate involutional changes with extensive fat necrosis, cyst formation, calcification and reactive bone formation. As a result the radiologic appearance of the lesion depends on its histologic composition (7,10-11). Milgram stage 1 lesions, which are solely composed of fat, are radiolucent, well-circumscribed lesions, are associated with mild focal expansion and remodelling of the bone especially in thin bones. Thin or occasionally thick trabecular ridges may be present in the periphery of the lesion and produce a septated appearance. Their radiographic appearance is nonspecific and share the same features as unicameral bone cyst, fibrous dysplasia and plasmocytoma. However CT and MRI can both show the intralesional fat and are important diagnostic modalities. On CT scans, the attenuation of normal marrow is slightly higher than that of lipoma. On MRI, the fat in the lesion shows higher signal intensity on both T1 and T2 weighted images than the fatty marrow, which shows subtle lower signal intensity. Milgram stage 2 or 3 lesions, in which the intraosseous lipomas are associated with various amounts of central or peripheral ossification or calcification may cause the typical central or ring like calcification in a lucent lesion involving the body of calcaneus. However the same calcification pattern in other less common locations may cause confusion. The ossification in these lesions may be extensive and be confused with enostosis. Partially mineralized lesions may look like chondroid lesions or osteonecrosis. Expansile Page 8 of 10

remodelling of the bone, osteolysis and rounded margins are helpful clues to differentiate intraosseous lipomas from osteonecrosis at CT or MRI. In stage 3 lesions, with progressive involution and ischemia, fibrous and cystic changes may predominate in the lesion and they may appear as unicameral bone cysts. Central cystic areas may be surrounded by a rim of ossification, which, then may be surrounded by fat, that in turn may be surrounded by a rim of ossification of a fibrous capsule, demarcating the periphery of the lesion, resulting in the distinctive "bull's eye" appearance. On isotope bone scans, negative or mild uptake may be encountered (8). Symptomatic cases may require curretage and bone graft placement. Recurrences and malignant transformation are rare (7). Although atypical location may require further evaluation and research, CT and MRI are efficient modalities for the diagnosis of intraosseous lipomas and bone biopsy may be rendered unnecessary. References 1. Teitelbaum SL. Twenty years' experience with soft tissue sarcomas of the chest wall at a large institution. J Thorac Cardiovasc Surg. 1972;63:585-6. 2. Nam SJ, Kim S, Lim BJ, Yoon CS, Kim TH, et al. Imaging of primary chest wall tumors with radiologic- pathologic correlation. Radiographics 2011;31:749-70. 3. Downey RJ, Huvos AG, Martini N. Primary and secondary malignancies of the sternum. Semin Thorac Cardiovasc Surg. 1999;11:293-6. 4. Restrepo CS, Martinez S, Lemos DF, Washington L, McAdams HP, et al. Imaging appearances of the sternum and sternoclavicular joints. Radiographics 2009;29:839-59. 5. Burt M. Primary malignant tumors of the chest wall. The Memorial Sloan- Kettering Cancer Center experience. Chest Surg Clin N Am. 1994;4:137-54. 6. Radiologic- pathologic correlation of intraosseous lipomas. AJR Am J Roentgenol. 2000;175:673-8. 7. Murphey MD, Carroll JF, Flemming DJ, Pope TL, Gannon FH et al. From the archives of the AFIP:benign musculoskeletal lipomatous lesions. Radiographics. 2004;24:1433-66. 8. Campbell RS, Grainger AJ, Mangham DC, Beggs I, Teh J et al. Intraosseous lipoma:report of 35 new cases and a review of the literature. Skeletal Radiol. 2003;32:209-22. Page 9 of 10

9. Solak O, Esme H, Sahin DA, Aktepe F. Giant intraosseous lipoma of the rib. Thorac Cardiovasc Surg. 2007;55:273-4. 10. Milgram JW. Intraosseous lipomas: radiologic and pathologic manifestations. Radiology. 1988;167:155-60. 11. Milgram JW. Intraosseous lipomas. A clinicopathologic study of 66 cases. Clin Orthop Relat Res. 1988:277-302. Personal Information Zehra Akkaya, MD Department of Radiology, Ankara University Faculty of Medicine Ankara- Turkey Caglar Uzun, MD Department of Radiology, Ankara University Faculty of Medicine Ankara- Turkey Serkan Enon, MD Department of Thoracic Surgery, Ankara University Faculty of Medicine Ankara- Turkey Gokhan Kocaman, MD Department of Thoracic Surgery, Ankara University Faculty of Medicine Ankara- Turkey Gulden Sahin, MD, Professor of Radiology Department of Radiology, Ankara University Faculty of Medicine Ankara- Turkey Page 10 of 10