Solitary Fibrous Tumors of the Soft Tissues: Review of the Imaging and Clinical Features With Histopathologic Correlation

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1 Musculoskeletal Imaging Clinical Perspective Wignall et al. Solitary Fibrous Tumors of Soft Tissues Musculoskeletal Imaging Clinical Perspective Oliver J. Wignall 1,2 Eleanor C. Moskovic 1 Khin Thway 3 Joseph M. Thomas 4 Wignall OJ, Moskovic EC, Thway K, Thomas JM Keywords: CT, extrathoracic, MRI, solitary fibrous tumors, thoracic DOI: /JR Received July 28, 2009; accepted after revision January 4, Department of Radiology, Royal Marsden Hospital, London, England. 2 Present address: Department of Radiology, Torbay Hospital, Laws ridge, Torquay TQ2 7, England. ddress correspondence to O. J. Wignall (oliver.wignall@nhs.net or oliverwignall@hotmail.com). 3 Department of Histopathology, Royal Marsden Hospital, London, England. 4 Department of Surgery, Royal Marsden Hospital, London, England. WE This is a Web exclusive article. JR 2010; 195:W55 W X/10/1951 W55 merican Roentgen Ray Society Solitary Fibrous Tumors of the Soft Tissues: Review of the Imaging and Clinical Features With Histopathologic Correlation OJECTIVE. Solitary fibrous tumors are rare soft-tissue tumors of submesothelial origin with variable malignant potential. Most of these tumors originate within the thoracic cavity, but they can occur in a variety of sites, including the abdomen, pelvis, and soft tissues and muscles. The purpose of this study was to review the imaging findings with clinicopathologic correlation in 34 cases. CONCLUSION. The finding of a large, solid, vascular tumor, particularly with prominent feeding vessels or a visible fatty component, should alert the radiologist to the possible diagnosis of solitary fibrous tumor. Percutaneous biopsy carries minimal risk and should be used for definitive diagnosis of these lesions, which in many cases are curable with surgery. The prognosis is good for patients with benign tumors but variable for those with malignant tumors. S olitary fibrous tumors (SFTs) are a rare group of spindle cell neoplasms that include fibrous-tocellular SFTs and related lesions such as lipomatous hemangiopericytoma and giant cell angiofibroma [1]. SFTs were first described as originating from the pleura [2] and occurring most commonly in the thoracic cavity [3, 4], but it is now recognized that these rare tumors can occur throughout the body [4 9]. The most commonly reported extrathoracic locations are the retroperitoneum, deep soft tissues of the proximal extremities, abdominal cavity, and head and neck [1]. SFTs principally affect adults in middle age with no sex predilection [1, 3, 10]. Most thoracic SFTs are asymptomatic at presentation and are diagnosed as incidental findings on radiographs and CT images of the chest [3, 4]. Extrathoracic SFTs, however, are usually symptomatic; the manifestations are a painless mass or local pressure effects, depending on location [4]. SFTs from all sites are usually benign, and surgical resection is curative in almost all cases [3, 4, 10]. Long-term followup is mandatory for all patients because in some cases clinical behavior does not correlate with the histopathologic appearance [1]. ecause of the rarity of SFTs, information on the imaging features is sparse. To our knowledge, there has been no report on the imaging features of a series of extrathoracic SFTs or on the imaging features of SFTs at all anatomic sites. To better characterize the radiologic features of these tumors, we undertook a retrospective study of SFTs managed at our institution that were found at any anatomic location. We reviewed images obtained with all available techniques, including CT, MRI, ultrasound, radiography, and angiography. The aim of this study was to characterize the radiologic features of these tumors at all anatomic locations and to make the histopathologic correlation. Materials and Methods The cases of 87 patients with SFTs referred to the soft-tissue sarcoma unit at our hospital from May 1997 to January 2009 were identified from our institutional pathology database. ll histopathologic specimens had been reviewed by an experienced soft-tissue tumor pathologist at this institution, who confirmed the diagnosis of SFT. If the initial CT or MR images were not available at our institution, they were requested from the referring hospital. total of 34 patients with SFTs who underwent preoperative CT or MRI were identified. Medical records were reviewed and patient age, sex, initial symptoms, treatment, follow-up imaging, and outcome were recorded. ll available images were reviewed independently by two radiologists. Disagreement regarding imaging findings was resolved by debate between the two radiologists. For each scan, the following imaging findings were recorded: lesion location, size, border, texture, and degree of enhancement. The presence or ab- JR:195, July 2010 W55

2 Wignall et al. Fig year-old woman with solitary fibrous tumor of pleura., Chest radiograph shows large mass in right upper zone with associated pleural effusion., Coronal contrast-enhanced CT image shows multifocal vascular tumor in right hemithorax with associated pleural effusion. sence of invasion of local structures, local lymph node involvement, and distant metastasis was recorded, as were other relevant imaging findings. For MRI, the signal characteristics of lesions were recorded. Clinical and imaging findings were correlated with the presence or absence of malignant features at histopathologic examination. Results The patients were 17 men and 17 women (median age, 51.5 years; range, years). In this cohort only three tumors (9%) originated in the pleura (Fig. 1). One of these patients had symptoms, the initial manifestation of the tumor being progressive peripheral edema. The manner of presentation was not documented for the other patients. The other 31 SFTs originated outside the thoracic cavity. The most common location was the soft tissues and muscles (17/34, 50%), followed by the pelvis (10/34, 29%) and abdomen (3/34, 9%) (Table 1). Most of the patients with extrathoracic SFTs (28/31, 90%) had symptoms at the initial evaluation. The most common initial symptom was a mass (24/31, 77%). The initial symptoms in the other patients were due to local pressure effects and included abdominal pain, change in bowel habit, and lower urinary tract symptoms. In one patient a pelvic mass was found incidentally during a routine cervical smear. None of the patients had hypoglycemia documented at initial evaluation. The tumors were commonly large at initial evaluation with mean dimensions of cm. In 19 of 34 cases (56%), the tumor measured 10 cm in maximum diameter. Metastatic disease occurred in only one of the 15 patients with tumors measuring < 10 cm in maximum diameter but occurred in eight of 19 patients with tumors measuring 10 cm in maximum diameter. In four patients, these tumors were seen at the initial evaluation, and in the other four patients metastasis developed after surgery. Regarding cross-sectional imaging, 22 patients (65%) underwent CT examinations (Fig. 2). Fifteen patients underwent CT only, 12 underwent MRI only, and seven patients underwent both CT and MRI. Three patients underwent additional ultrasound and angiographic imaging (Fig. 3). The imaging findings are summarized in Table 2. The tumor contour was lobulated in 21 of the 34 cases (62%). ll tumors had discrete margins. vid enhancement after IV contrast administration was present in 15 of 26 tumors (58%). Twenty-seven of the 34 SFTs (79%) had a heterogeneous enhancement pattern. Calcification was present in only three of the 34 tumors (9%). Collateral feeding vessels were present in 12 of the 34 SFTs (35%). These vessels were clearly seen with CT, MRI, ultrasound, and angiography (Figs. 3 and 4). Subsequent histopathologic examination of these 12 tumors revealed 11 typical fibrous-to-cellular SFTs and one lipomatous hemangiopericytoma. TLE 1: natomic Locations of 34 Solitary Fibrous Tumors Site No. of Tumors Percentage Soft tissues/musculature Proximal extremity uttock 3 9 nterior abdominal wall 1 3 Chest wall 1 3 ack 1 3 Distal extremity 1 3 Pelvis bdomen 3 9 Pleura 3 9 reast 1 3 W56 JR:195, July 2010

3 Solitary Fibrous Tumors of Soft Tissues Fig year-old woman with mass in right thigh., xial enhanced CT image shows well-defined heterogeneously enhancing soft-tissue mass in adductor compartment of right thigh., Coronal reformatted image shows prominent collateral feeding vessels better than does (arrows). Invasion of local structures was present in only three of 34 (9%) cases. No patient had local or distant lymphadenopathy at initial evaluation. Distant metastasis was present at initial imaging in four of the 34 patients (12%). Metastatic spread to the lungs was found at initial evaluation in three of the four patients. The fourth patient had widespread metastatic disease in the liver, peritoneum, and retroperitoneum. In all four patients the tumor was large ( 10 cm in maximum diameter) and had features suggesting either malignant potential or overt malignancy at subsequent histopathologic examination. Nineteen patients underwent MRI (Fig. 5). In 17 of the 19 patients (89%), the tumor had high signal intensity on T2-weighted images and intermediate signal intensity on T1- weighted images. Flow voids corresponding to prominent perilesional vessels were seen in the larger tumors. In two cases, high signal intensity was seen on T1-weighted images, suggesting the presence of intralesional fat (Figs. 6 and 7). This finding was confirmed at histopathologic examination, which revealed lipomatous hemangiopericytoma. ll tumors were initially diagnosed with 14-gauge percutaneous core-cut biopsy, in some cases with imaging guidance. The risk associated with this procedure is minimal. We found only four case reports of tumor seeding of sarcomas after percutaneous core biopsy [11 13]. Incisional biopsy was not performed because of the established risk of tumor seeding [14]. Thirty of the 34 patients (88%) underwent surgical resection. Three of these patients underwent further treatment with adjuvant radiotherapy for the following reasons: high-grade malignancy, narrow excision margins, and a large, rapidly growing tumor. The group of patients treated surgically and evaluated further included 28 patients treated with curative intent and two patients with pleural SFTs and contralateral pulmonary metastasis who underwent debulking surgery. In one of the postsurgical patients, no follow-up findings were documented in the medical records. The median follow-up period for the other 29 patients treated with surgery was 12 months (range, 0 71 months). One patient with a large vascular tumor in the pelvis died of uncontrolled hemorrhage during surgery, after a previous failed attempt at debulking at another institution. During the relatively short follow-up period, three of the patients treated surgically with curative intent were found to have distant metastasis (24, 7, and approximately 6 12 months after surgery). One patient was found to have locally recurrent disease in the pelvis 11 months after surgery. Followup CT of two of the patients treated surgically with curative intent showed small areas of residual enhancing soft tissue at the surgical site. These patients were undergoing continued close follow-up at the end of this study. oth patients with metastatic disease at initial evaluation and treated with debulking surgery were found to have progressive metastatic disease at follow-up CT 4 months after surgery for one patient and 6 months for the other. Metastasis had occurred in the lungs, liver, and soft tissues. Four patients were treated nonsurgically for the following reasons. Two patients had highly vascular pelvic tumors, and in both TLE 2: Imaging Findings of 34 Solitary Fibrous Tumors Contour Imaging Finding No. of Tumors Percentage Smooth Lobulated Margin Discrete Degree of enhancement High Intermediate 9 26 None 1 3 Contrast not given 2 6 Enhancement pattern Heterogeneous Homogeneous 5 15 Contrast not given 2 6 Calcification Present 3 9 bsent Collateral feeding vessels Present bsent Invasion of local structures Present 3 9 bsent JR:195, July 2010 W57

4 Wignall et al. cases initial observation was recommended because of the potential risks of surgery. One of these two patients with pelvic tumors was found to have pulmonary metastasis at initial evaluation. The third patient treated nonsurgically had widespread metastatic disease at initial evaluation and did not need surgery for symptom control. fter an initial watch and wait policy, follow-up CT showed disease progression, and the patient underwent palliative doxorubicin chemotherapy. The fourth patient treated nonsurgically had a right hemipelvic mass in the iliopsoas tendon, adjacent to the femoral nerve, at initial evaluation. Percutaneous biopsy showed a low-grade tumor (< 1 mitosis per high-power field), and the patient had only minor symptoms and was keen to avoid surgery. The decision was made to watch and wait, and two subsequent MRI examinations showed the tumor unchanged in size and appearance. Fifteen of the 17 patients with no specific features of malignancy at histopathologic examination underwent surgery. Fourteen patients were disease-free after a median followup period of 5 months (range, 1 41 months). No follow-up information was available for the other patient. Metastatic disease occurred in eight of the 17 patients with histopathologic findings of either malignant potential or overt malignancy. In one half of these patients, metastatic disease was found at initial evaluation. Fig year-old man with pelvic solitary fibrous tumor., xial contrast-enhanced CT image shows avidly enhancing lobulated soft-tissue mass in left hemipelvis with large collateral feeding vessels (arrows)., Digital subtraction angiogram clearly shows feeding vessels, which were embolized before surgery. In the other patients, metastasis developed an average of 12.8 months after surgery (range, 7 24 months). Histopathologic examination of three tumors showed lipomatous hemangiopericytoma, and all three tumors were surgically resected. In two of these cases intralesional fat was clearly found at CT and MRI (Figs. 6 and 7). Histologically, SFTs are composed of patternless distributions of closely packed spindle cells with varying degrees of fibrosis and interspersed branching staghornshaped vessels (Fig. 8). Immunohistochemically, SFTs characteristically as many as 95% of cases have a positive CD34 result (Fig. 9). Lipomatous hemangiopericytoma Fig year-old woman with mass in left lower extremity. and, Coronal T1-weighted () and fat-suppressed () contrast-enhanced MR images show well-defined, enhancing soft-tissue mass in medial compartment of calf. Feeding vessels have low signal intensity due to flow void (arrow). W58 JR:195, July 2010

5 Solitary Fibrous Tumors of Soft Tissues Fig year-old woman with mass in distal right thigh., Coronal T1-weighted MR image shows well-defined mass of low signal intensity., Coronal STIR MR image shows tumor of high signal intensity and edema in surrounding muscle (arrow). C, Contrast-enhanced fat-suppressed MR image shows heterogeneous enhancement. is a rare variant of SFT that contains a variable amount of mature adipose tissue, which can be seen grossly or only microscopically [15, 16]. lthough some lipomatous hemangiopericytomas have recurred, to date and to our knowledge, none has been known to metastasize. The criteria for malignancy of SFTs vary from study to study, but malignant lesions are hypercellular with at least focal moderate to severe nuclear atypia. They often have infiltrative margins with surrounding tissue, exhibit tumor necrosis, and have 4 mitoses per 10 high-power fields [9, 17]. ll 34 cases were reviewed histologically. Of these, 31 were diagnosed as SFT and three as lipomatous hemangiopericytoma. Seventeen tumors were classified as benign, eight as having malignant potential (i.e., having some of the features of malignancy), and nine as exhibiting overt malignancy. ll nine malignant tumors were hypercellular lesions, and of these, three each had mild to moderate atypia, and three displayed marked atypia. Twelve tumors had at least focal necrosis. The mitotic index ranged from 4 to 35 per 10 high-power fields, but of the two tumors that had fewer than 4 mitoses per 10 high-power fields, one displayed marked cellular atypia and both had marked necrosis associated with malignancy. The result of CD34 immunohistochemi- C JR:195, July 2010 W59

6 Wignall et al. cal staining was diffusely positive in 30 of the 33 tumors and focally positive in three tumors, all benign SFTs. The CD34 result was negative in only one tumor, a benign lipomatous hemangiopericytoma, but this lesion had characteristic architectural features and a positive result for CD99 and bcl-2. C C D D Fig year-old man with pelvic mass. D, xial T2-weighted (), T1-weighted (), fatsuppressed T1-weighted (C), and fat-suppressed (D) contrast-enhanced T1-weighted MR images show soft-tissue mass in right ischiorectal fossa. Mass exhibits high signal intensity in and and central loss of signal intensity on fat-suppressed images. Peripheral nonfatty component exhibits contrast enhancement. Histologic finding was lipomatous hemangiopericytoma. Discussion Review of the literature reveals limited information on the imaging features of SFTs. Two reports document the CT appearance of pleural SFTs. In a series of 26 cases, Cardinale et al. [18] found the typical appearance of well-defined, lobulated lesions with a geographic pattern of enhancement. In a smaller series of pleural SFTs [19], the typical CT findings of well-marginated, lobulated masses of soft-tissue attenuation were made. The literature on the imaging features of extrathoracic SFTs comprises mainly case reports [20 25]. To our knowledge, there has been no Fig year-old woman with mass of posterior thoracic wall., xial contrast-enhanced CT image shows well-defined soft-tissue mass with central fatty component (arrow)., xial T1-weighted MR image shows fatty component as area of high signal intensity. C, xial STIR MR image shows soft-tissue component of tumor as area of high signal intensity. D, xial contrast-enhanced fat-suppressed T1- weighted MR image shows soft-tissue component enhanced whereas fatty component has low signal intensity (arrow). Histologic finding was lipomatous hemangiopericytoma. W60 JR:195, July 2010

7 Solitary Fibrous Tumors of Soft Tissues Fig year-old woman with solitary fibrous tumor resected from left thigh. Photomicrograph shows tumor has variable cellularity and comprises patternless distributions of spindle cells without atypia within collagenous stroma with interspersed angulated hemangiopericytic staghorn-shaped vessels (arrows). (H and E, 40) previous report on the imaging features of a large series of extrathoracic SFTs and SFTs from numerous anatomic sites. In this study, we identified 34 patients with SFTs who were treated at a single institution over an 11-year period and had cross-sectional images available. The imaging findings were reviewed in detail and correlated with the histopathologic features and clinical follow-up results. Several conclusions can be drawn about this series of patients. SFTs are very rare and appear to occur with equal frequency in men and women. lthough SFTs are reported to occur most commonly in the thoracic cavity [3, 4], in this series only three of 34 cases were intrathoracic. Our results are skewed, however, because most patients with intrathoracic SFTs in England are referred for surgery to a neighboring tertiary referral center. SFTs are large tumors, measuring 10 cm in maximum dimension in 19 of the 34 cases (56%). Most of the extrathoracic SFTs were symptomatic at initial evaluation, usually manifesting either a mass or local pressure effects. It has been reported [3] that approximately 5% of SFTs are associated with hypoglycemia due to secretion of insulinlike growth factors. This finding was not documented in any of the study patients. In this study, all tumors had discrete margins, and 21 of the 34 (62%) had a lobulated contour. SFTs were typically well defined, tending to displace adjacent structures. Local invasion was present in only three of the 34 cases (9%). Tumors were usually highly vascular and had avid contrast enhancement in 22 of the 34 tumors (65%). Twenty-seven of the 34 SFTs (79%) had a heterogeneous enhancement pattern. The differential diagnosis of a solitary, highly vascular soft-tissue lesion includes Fig year-old woman with solitary fibrous tumor resected from left thigh. Photomicrograph shows tumor has diffuse positive immunohistochemical result for CD34. high-grade sarcoma (alveolar soft-part sarcoma, malignant fibrous histiocytoma, and leiomyosarcoma), angiosarcoma, and a solitary vascular metastatic lesion, as from renal cell carcinoma. useful distinguishing imaging feature of SFTs is the presence of large collateral feeding vessels, which were seen in 12 of the 34 cases (35%). lthough it is not specific, this finding is helpful when present and can aid the radiologist in narrowing the differential diagnosis. The feeding vessels can be seen with CT, MRI, ultrasound, and angiography and were present in 11 of 31 fibrous-to-cellular SFTs and one of three lipomatous hemangiopericytomas. The presence of these vessels therefore does not seem to be related to the histologic subtype of the tumor. Similar vessels also can be seen in alveolar soft-part sarcoma, and percutaneous core biopsy is required for definitive diagnosis. Cardinale et al. [18] found prominent intralesional vessels in approximately one fourth of their cases. Calcification was present in only three of the 34 patients (9%). Distant metastatic lesions were present at initial imaging of four of the 34 patients (12%), most commonly in the lungs. No patient had local or distant lymph node involvement, according to imaging criteria, at initial evaluation. MRI features were relatively nonspecific. In 17 of 19 cases (89%), tumors had high signal intensity on T2-weighted images and intermediate signal intensity on T1-weighted images. reas of low signal intensity were seen in the larger tumors, corresponding to flow voids from prominent perilesional vessels. Lipomatous hemangiopericytoma is a subtype of SFT that contains fat. This series included three such lesions, and in all cases intralesional fat was readily seen on crosssectional images. CT depicted multiple intralesional low-attenuation foci, and MRI showed areas of high signal intensity on unenhanced T1-weighted images. Surgical resection is the treatment of choice and is curative in almost all cases of benign SFT [3, 4, 10]. In this study 15 of the 17 SFTs with no specific features of malignancy at histopathologic examination were surgically resected, and 14 of these patients were disease-free at the end of the study. No follow-up information was available for the other patient. It was found that the vascular nature of the tumors and the presence of large collateral feeding vessels frequently made surgical removal technically difficult. SFTs should therefore be dealt with in specialist tertiary referral centers, and embolization may be required before tumor removal. This technique was used preoperatively in two of the cases described. Reported rates of local recurrence and metastasis of extrathoracic SFTs vary [4, 7, 8]. In our study, 28 patients with extrathoracic SFTs were treated surgically with curative intent. Three of these 28 patients (11%) subsequently were found to have metastatic disease. These findings agree with those of Gold et al. [4] and Vallat-Decouvelaere et al. [7] but not with a report by runnemann et al. [8] in which none of 24 patients with extrathoracic SFTs had either local recurrence or metastatic disease. Gold et al. compared thoracic with extrathoracic SFTs. small but statistically significant increased risk of local disease recurrence was found in extrathoracic SFTs. No difference in metastasis-free survival was found between thoracic and extrathoracic SFTs. In our study, the number of thoracic tumors was too small to allow comparison with extrathoracic SFTs. Tumors with a histologically malignant component and those 10 cm in maximum diameter are reported to be associated with significantly higher risk of local disease recurrence and metastatic disease [4]. Our findings agree with that report; these patients therefore need close follow-up after surgery. Metastasis occurred in eight of the 17 tumors (47%) with either malignant potential or overt malignancy and in eight of 19 tumors (42%) measuring 10 cm in maximum diameter. Conversely, metastasis occurred in only one of the 17 patients with no specific features of malignancy and in only one of the 15 patients with tumors measuring < 10 cm in maximum diameter. JR:195, July 2010 W61

8 Wignall et al. The presence of a large, highly vascular softtissue tumor with prominent collateral feeding vessels or a visible fatty component should alert the radiologist to the possible diagnosis of SFT. Percutaneous biopsy carries minimal risk of tumor seeding and is recommended for diagnosis. Patients with these findings should be referred to a specialist center for surgical assessment, and long-term follow-up is mandatory for all patients. The prognosis is good for tumors with no specific features of malignancy, and surgery, if technically feasible, usually is curative. The outcome is worse for potentially or overtly malignant tumors and for tumors measuring 10 cm. cknowledgment We thank Omar l-muderis, data manager, Sarcoma Unit, Royal Marsden Hospital, for coordinating data collection. References 1. Gengler C, Guillou L. Solitary fibrous tumour and haemangiopericytoma: evolution of a concept. Histopathology 2006; 48: Klemperer P, Rabin C. Primary neoplasms of the pleura: a report of five cases. rch Pathol 1931; 11: Enzinger FM, Weiss SW. Solitary fibrous tumor. In: Enzinger FM, Weiss SW, eds. Soft tissue tumors. St. Louis, MO: Mosby, 1995: Gold JS, ntonescu CR, Hajdu C, et al. Clinicopathologic correlates of solitary fibrous tumors. Cancer 2002; 94: Fukunaga M, Naganuma H, Nikaido T, Harada T, Ushigome S. Extrapleural solitary fibrous tumor: a report of seven cases. Mod Pathol 1997; 10: Nielsen GP, O Connell JX, Dickersin GR, Rosenberg E. Solitary fibrous tumor of soft tissue: a report of 15 cases, including 5 malignant examples with light microscopic, immunohistochemical, and ultrastructural data. Mod Pathol 1997; 10: Vallat-Decouvelaere V, Dry SM, Fletcher CD. typical and malignant solitary fibrous tumors in extrathoracic locations: evidence of their comparability to intra-thoracic tumors. m J Surg Pathol 1998; 22: runnemann R, Ro JY, Ordonez NG, Mooney J, El-Naggar K, yala G. Extrapleural solitary fibrous tumor: a clinicopathologic study of 24 cases. Mod Pathol 1999; 12: Hasegawa T, Matsuno Y, Shimoda T, Hasegawa F, Sano T, Hirohashi S. Extrathoracic solitary fibrous tumors: their histological variability and potentially aggressive behavior. Hum Pathol 1999; 30: England DM, Hochholzer L, McCarthy MJ. Localized benign and malignant fibrous tumors of the pleura: a clinicopathologic review of 223 cases. m J Surg Pathol 1989; 13: Davies NM, Livesley PJ, Cannon SR. Recurrence of an osteosarcoma in a needle biopsy track. J one Joint Surg r 1993; 75: Ferguson PC, Sommerville S, Grimer RJ. Possible metastasis of osteosarcoma to a remote biopsy site: a case report. Clin Orthop Relat Res 2004; (424): Schwartz HS, Spengler DM. Needle tract recurrences after closed biopsy for sarcoma: three cases and review of the literature. nn Surg Oncol 1997; 4: Hoeber I, Thomas JM. iopsy methods of choice in soft-tissue sarcomas. Eur J Surg Oncol 1999; 25: Folpe L, Devaney K, Weiss SW. Lipomatous hemangiopericytoma: a rare variant of hemangiopericytoma that may be confused with liposarcoma. m J Surg Pathol 1999; 23: Ceballos KM, Munk PL, Masri, O Connell JX. Lipomatous hemangiopericytoma: a morphologically distinct soft tissue tumor. rch Pathol Lab Med 1999; 123: Fukunaga M, Naganuma H, Ushigome S, Endo Y, Ishikawa E. Malignant solitary fibrous tumour of the peritoneum. Histopathology 1996; 28: Cardinale L, llasia M, rdissone F, et al. CT features of solitary fibrous tumour of the pleura: experience in 26 patients. Radiol Med 2006; 111: Lee SC, Tzao C, Ou SM, Hsu HH, Yu CP, Cheng YL. Solitary fibrous tumors of the pleura: clinical, radiological, surgical and pathological evaluation. Eur J Surg Oncol 2005; 31: Johnson TR, Pedrosa I, Goldsmith J, Dewolf WC, Rofsky NM. Magnetic resonance imaging findings in solitary fibrous tumor of the kidney. J Comput ssist Tomogr 2005; 29: Wat SY, Sur M, Dhamanaskar K. Solitary fibrous tumor (SFT) of the pelvis. Clin Imaging 2008; 32: Nath DS, Rutzick D, Sielaff TD. Solitary fibrous tumor of the liver. JR 2006; 187:491; W187 W Chun HJ, yun JY, Jung SE, Kim KH, Shinn KS. enign solitary fibrous tumour of the pre-sacral space: MRI findings. r J Radiol 1998; 71: Game P, Roberts-Thomson IC. Education and imaging. Gastrointestinal: solitary fibrous tumor. J Gastroenterol Hepatol 2006; 21: Kinoshita T, Ishii K, Higashiiwai H, Naganuma H. Malignant solitary fibrous tumour of the peritoneum. Clin Radiol 2000; 55: W62 JR:195, July 2010