Musculoskeletal ImagingFrick et al.

Frick et al. T2 Characteristics of Desmoplastic Fibroma of Bone Musculoskeletal ImagingFrick et al. Matthew A. Frick 1 Murali Sundaram 1,2 Krishnan K. Unni 3 Carrie Y. Inwards 3 Nicola Fabbri 4 Federico Trentani 4 Patrizia Baccini 5 Franco Bertoni 5 Received July 21, 2004; accepted after revision September 9, 2004. 1 Department of Radiology, Mayo Clinic, West-2, 200 First Street, SW, Rochester, MN 55905. Address correspondence to M. A. Frick. 2 Present Address: Department of Radiology, Cleveland Clinic Foundation, 9500 Euclid Ave., Cleveland, OH 44915. 3 Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, Minnesota. 4 Servizio di Ortopedico, Istituto Ortopedico Rizzoli, Bologna, Italy. 5 Servizio di Anatomia e Istologia Patologica, Istituto Ortopedico Rizzoli, Bologna, Italy. AJR 2005;184:1762 1767 0361 803X/05/1846 1762 American Roentgen Ray Society Original Report Imaging Findings in Desmoplastic Fibroma of Bone: Distinctive T2 Characteristics OBJECTIVE. The purpose of this study was to evaluate the imaging features of desmoplastic fibroma of the bone, with an emphasis on MRI signal characteristics. CONCLUSION. Significant T2 shortening of a nonsclerotic fibroosseous lesion should place desmoplastic fibroma high among the diagnostic considerations. n 1958, Jaffe [1] first described I desmoplastic fibroma of the bone as a distinct entity when he documented five cases of a previously unclassified osseous fibrous tumor that histologically was similar to abdominal desmoid tumor. Desmoplastic fibroma of the bone is now considered the intraosseous counterpart of the common soft-tissue desmoid or fibromatoses [2]. This rare bone tumor is most frequently described in single case reports. The largest series in the radiology literature [3] consists of 18 cases and primarily discusses the radiographic features of the tumor. To our knowledge, no series has analyzed the MRI characteristics of desmoplastic fibroma of the bone. On the basis of material obtained from the pathology files at two institutions, we describe and discuss the imaging features of desmoplastic fibroma of the bone, with an emphasis on radiologic and MRI characteristics. We compared our MRI findings with descriptions in a previous case report [4], paying special attention to the frequency and extent of the T2 shortening within the lesion. A short T2 is rarely encountered in lytic bone lesions and soft-tissue masses. One common soft-tissue lesion that may have a short T2 is fibromatosis [5, 6]. The purpose of this study was to determine whether a short T2 applies to its intraosseous counterpart with any frequency and, if so, to semiquantitatively describe its extent within a lesion and discuss its value as a diagnostic sign in the realm of fibroosseous lesions of the bone. Materials and Methods We retrospectively reviewed the pathology files at two institutions with an orthopedic oncology referral practice for cases of tumors classified as desmoplastic fibroma of the bone. We found 96 cases. The histology in all cases at both locations was reviewed by four pathologists, two from each institution. One case was excluded because the pathologists thought it represented a nonossifying fibroma. This left 95 patients in the study. The medical records or consultation letters were reviewed to determine the patients sex and age at the time of lesion discovery. Of the 95 patients, 45 had some form of imaging study (i.e., radiology, CT, MRI, or a combination) available for review. Radiographs of 38 patients were evaluated to determine the lesion s location, site within the bone, matrix, cortical integrity, margins, and size. CT images were available for 17 patients, 14 of whom had corresponding radiographs and six, corollary MR images. The CT images were evaluated for lesion matrix, cortical integrity, and the presence of associated soft-tissue mass. A soft-tissue mass was considered present when extraosseous extent of tumor with breeched cortex and periosteum were noted. MRI was performed on multiple magnets on two continents; conventional T1-weighted images were available for all 14 patients. The files of nine patients also included conventional T2-weighted images; in two 1762 AJR:184, June 2005

T2 Characteristics of Desmoplastic Fibroma of Bone Fig. 1. Anteroposterior radiograph of pelvis of 30-year-old man shows well-marginated, nonsclerotic, osteolytic lesion (white box) of left superior pelvis that extends into left superior pubic ramus abutting pubic symphysis. A few thin, internal bony ridges are present. Fig. 2. Lateral radiograph of right forearm of 75-yearold man shows long, well-marginated, unmineralized, ulnar diaphyseal lesion with associated endosteal scalloping. Lesion has no significant trabeculations. cases the exact TR and TE were unknown, but images were determined to be T2. The files of four patients included proton-density (PD) images and the file of one patient, T1-weighted images in isolation. Of patients with MR images, 10 had corresponding radiographs and six, corresponding CT images. MR images were reviewed to determine cortical integrity, soft-tissue mass and concordance with radiographic dimensions of the intraosseous component of the lesion, and the signal relationship to muscle on T1- and T2-weighted sequences. In lesions with areas of short T2, the extent of the area as a percentage of lesion size was estimated as less than 25%, 25 50%, 50 75%, or greater than 75%. Exact MR scanning parameters were available for 11 patients and were partially known in another case. T1-weighted images ranged from 430 683 msec (TR) and 9 25 msec (TE). T2-weighted sequences ranged from 1,800 5,300 msec and 90 117 msec, respectively. Proton density weighted images were available for four patients; the TR ranging from 2,000 2,240 msec and the TE, from 30 39 msec. Spoiled gradient recalled echoes were also available for one patient, fat-saturated T2 sequences for three patients, and PD fat-saturated sequences for one patient. Gadoliniumenhanced images were available for two patients. The images were also reviewed for the presence of associated pathologic fractures. The imaging findings were documented by two radiologists working in consensus who were aware of the diagnosis at time of review. Institutional review board approval of the study was obtained. Results The sex of 93 patients was known; there was a slight predominance of men (56 versus and 37 women). At time of diagnosis, the age of the patients, which was not known in two cases, was between less than 1 year and 86 years (mean, 26.3 years). Based only on available imaging, there were 27 lesions within the tubular bones; four were diaphyseal, nine metadiaphyseal, nine metaphyseal, and five epiphyseal (juxtaarticular). The lesions were located centrally in 61% of patients and eccentrically in 39%. The host bone in the remaining 18 cases was the calcaneus (n = 4), pelvis (n = 6), mandible (n = 4), vertebrae (n = 3), and skull base (n = 1). Radiographs showed the matrix was osteolytic in 9 lesions (24%) (Figs. 1 and 2), osteolytic with coarsened ridge-like trabeculae in 24 lesions (63%) (Fig. 3), and mixed lytic and mildly sclerotic in five lesions (13%) (Figs. 4A and 4B). Cortical breaching was present in 20 (53%) of 38 lesions (Fig. 3). Radiology showed the margins were well defined in 13 lesions (34%) (Figs. 1 and 2), partially well defined in 23 lesions (61%), and not well seen in two lesions (5%). The margins were sclerotic in 46% of lesions. The average size of the lesions was 8.1 3.9 cm in greatest longitudinal and transverse dimensions, respectively (range, 3 16 cm and 1.5 9 cm, respectively). Five patients (13%) had evidence of pathologic fracture. CT revealed osteolytic (65%) (Fig. 4C) or mixed osteolytic and mildly sclerotic (35%) matrix patterns. Cortical destruction was seen on CT in 15 (88%) of 17 patients (Fig. 4C) and a soft-tissue mass extending beyond the original destroyed cortex, in seven patients (41%). In all cases, T1-weighted sequences showed that the signal intensities within the lesions were isointense or hypointense to adjacent normal muscle (Figs. 5 and 6). Lesions were at least in part isointense or hypointense to muscle in eight (89%) of nine cases for which conventional T2-weighted spin-echo or fat-saturated sequences were available (Figs. 7 11). The one case in which the lesion did not contain areas of low T2 signal was confounded by the presence of an associated pathologic fracture, and much of the increased signal intensity may have been caused by edema. In the eight lesions with short T2, the low signal encompassed more than 75% of the tumor in five cases and between 50% and 75% in three cases. In no case with a low T2 signal in the lesion did the amount of low signal encompass less than 50% of the tumor. In one patient, PD sequences showed high signal. Conventional and other T2-weighted sequences were not available for this patient. AJR:184, June 2005 1763

Frick et al. On the fat-suppressed sequences, the lesions remained hypointense to muscle (Figs. 7 and 11). In two patients for whom gadolinium-enhanced images were available, the lesions had prominent but somewhat heterogeneous enhancement. There was no significant discordance between radiographic and MR images in the intraosseous extent of the tumor. Discussion Desmoplastic fibroma of the bone, the intraosseous counterpart of soft-tissue fibromatoses, also is known as desmoid tumor of bone. Desmoplastic fibromas account for up to 0.1% of primary bone tumors [2]. Recognition of desmoplastic fibroma is important because on radiology and histology, the lesion may be mistaken for an indolent, benign fibrous lesion or more aggressive spindle-cell sarcomas [7]. Because of its relative rarity, desmoplastic fibroma of the bone has been described in only a few small series in the orthopedic, pathology, and radiology literature. Cumulatively, these series are far outnumbered by single case reports. In our series comprising a selected population from two referral centers, the tumor was seen most frequently in patients in the third decade of life. In other series, they have been found in the third to fourth decade [3, 7, 8]. Reports of the sex distribution of patients with this tumor are conflicting. Crim et al. [8] reviewed 107 cases in the literature, in addition to their seven cases, and did not find a predisposition based on sex predilection. Results in reviews of fewer patients suggest a slight predominance of men [5]. In our series, the sex was known in 93 patients and the male female ratio was 1.5:1. The only two series examining the radiologic features of desmoplastic fibroma of bone [3, 8] emphasize that the lesion is osteolytic and does not contain significant mineralized matrix (Figs. 1 and 2) with a favored metaphyseal origin. In a review of 79 published radiographs and their seven cases, Crim et al. [8] found only six cases in the diaphysis. The authors also emphasize the presence of ridges of intact bone near the periphery that are the result of uneven bone destruction (Fig. 3). These observations were largely borne out by our review, in which metaphysis and diametaphysis were equally involved and exclusive diaphyseal involvement of a tubular bone (4 of 27, 15%) was the rarest site (Fig. 2). In the series by Taconis et al. [3], the most common location in a long bone was the diametaphysis; only one lesion A Fig. 3. Anteroposterior (A) and lateral (B) radiographs of distal right femur in 30-year-old man show large eccentric lesion in femur that, unlike in Figs. 1 and 2, reveal markedly coarse trabeculations within lesion and cortical breaching posterolaterally. Fig. 4. Anteroposterior (A) and lateral (B) radiographs of upper lumbar spine in 24-year-old man show well-defined osteolytic lesion of L2 vertebra with extension into pedicle. A few thin, internal trabeculae also are present. C, Unenhanced axial CT of same patient shows predominately osteolytic lesion with mild central sclerosis and cortical breaching. A B B C 1764 AJR:184, June 2005

T2 Characteristics of Desmoplastic Fibroma of Bone Fig. 5. T1-weighted MR image (TR/TE, 460/50) of 30-year-old man also shown in Fig. 1 shows lesion in pelvis is isointense with muscle and entirely intracompartmental. Fig. 6. Axial T1-weighted image (TR/TE, 700/16) of ulnar diaphysis in 75-year-old man also shown in Figs. 2 and 8 shows lesion is isointense to muscle. Fig. 7. Coronal PD-weighted image (TR/TE, 4,560/39) image of 30-year-old man also shown in Figs. 1 and 5. More than 75% of lesion has T2 shortening, making it virtually indistinguishable from surrounding muscle. Peripheral signal intensity is high. Fig. 8 Axial T2-weighted MR image (TR/TE, 2,000/80) of right ulna of 75-year-old man also shown in Figs. 2 and 6 shows more than 75% T2 shortening of long, osteolytic lesion. included in their series was exclusively diaphyseal in location. At the time of discovery, the average size of the lesions in our study was approximately 8 4 cm, with cortical breaching a common finding (53%). Cross-sectional imaging revealed a soft-tissue mass in 41% of cases on CT and in 57% of cases on MRI. The morphologic appearance on the images was that of a relatively slow-growing lesion with focal aggressive features. The spectrum of radiologic features of desmoplastic fibroma of the bone overlap the radiographic patterns described for low-grade central osteosarcoma [9], and in some cases without cortical breaching may resemble fibrous dysplasia. The histologic distinction between these entities and fibrosarcoma, especially on a percutaneous bone biopsy, can be difficult, which has obvious management ramifications. Case reports of desmoplastic fibroma of the bone mention the presence of low to intermediate signal intensity on T2-weighted MRI sequences and vary in the degree of emphasis on this observation. In 2000, Vanhoenacker et al. [4] described a large desmoplastic fibroma of the femur and also tabulated the MRI features in 17 additional cases. In six of the cases, the T2-weighted sequences were not illustrated; in seven cases, the authors refer to the presence of a low or intermediate signal on T2-weighted sequences. Subsequently, two reports [10, 11] have described this tumor in vertebra, highlighting the rare location. In both cases, T2-weighted sequences showed a large lesion that was isointense and minimally hyperintense to muscle. The three patients with vertebral lesions in our series had marked T2 shortening (Figs.7 10). In 11 of 14 patients for whom MR images with T2- weighted sequences were available for review, the most common signal of the lesion was low, occupying more than 75% of the lesion in six patients and between 50% and 75% in three patients. Irrespective of location (i.e., long tubular bone, small tubular bone, pelvis, or vertebra), a short T2 was the predominant signal pattern (Figs. 5 10). Foci of short T2 in osteolytic lesions of the bone have been described in giant-cell tumors, fibrous dysplasia, lymphoma, and leiomyosarcoma [12 15]. T2 shortening in giant cell tumors was attributed to hemosiderin [13]. Foci of collagen were believed to contribute to short T2 in fibrous dysplasia [12]. The cause in lymphoma was unresolved because there was no histologic correlation with fibrosis [14]. In leiomyosarcoma, it was AJR:184, June 2005 1765

Frick et al. speculated that the muscle component of the tumor was responsible for the short T2 [15]. A review of the osseous component of the lesion in illustrations in these papers suggests that a predominance of T2 signal is most apparent in giant-cell tumors [9] and leiomyosarcomas. Histologically, neither type of tumor enters into the differential diagnosis of osseous desmoid and thus would not be mistaken for that entity. The short T2 in patients with leiomyosarcoma of the bone was noted only on non fat-suppressed, T2- weighted, spin-echo sequences; on the fatsuppressed sequences, all tumors were hyperintense. In our series, four patients had T2- weighted, fat-saturated sequences; two had more than 50% and two more than 75% of T2 shortening within the tumor. A predominantly osteolytic lesion with a large area of T2 shortening has a limited differential diagnosis. It appears this feature in osseous desmoid distinguishes it from lesions that it could be mistaken for tissue from a percutaneous biopsy. In this series, a diagnosis of desmoplastic fibroma could be made in one patient (Fig. 10) seen in consultation by one of us, even though it was unclear whether there was a histologic difference between the two lesions. Surgery was appropriately performed, and desmoplastic fibroma was histologically confirmed. The tumor in one patient in our series had a long T2; however, it was associated with a pathologic fracture. Another patient had a long T2 on PD images, and the lesion would probably have been hyperintense on a T2- weighted sequence. It is likely the lesion was more cellular than the others in our series, although the pathologist could not confirm this speculation. This patient had been seen by pathologists at other institutions whose opinions were divided between desmoplastic fibroma and grade 1 fibrosarcoma (Unni K, personal communication, March 1, 2002). In either case, the management for the two types of tumors is similar. Although the preponderance of lesions with T2 weighting in our series (90%) and in previous case reports had significant T2 shortening, we anticipate the finding will be absent in some patients, as was the case with the evolutionary MRI experience of soft-tissue desmoids. This study, however, confirms that the MRI signal characteristics of desmoplastic fibroma of the bone is shared by a subset of its soft-tissue counterpart, analogous to the histologic similarities of this tumor in bone and soft tissue. The radiologic features of a predominantly Fig. 9. Sagittal T2-weighted image (TR/TE, 2,000/80) of lumbar spine of 24-year-old man also shown in Fig. 4 shows T2 shortening of almost entire lesion. Entire involved vertebral body is slightly lower in signal intensity than surrounding normal vertebral bodies. Fig. 10. 42-year-old man with vertebral lesion that had been percutaneously biopsied. Histologic differential diagnosis was fibrous dysplasia versus desmoplastic fibroma. Axial T2-weighted image (TR/TE, 4,000/88) shows more than 90% of lesion is hypointense to muscle, favoring diagnosis of desmoplastic fibroma. Fig. 11. Axial T2-weighted image (TR/TE, 5,300/117) of calcaneus in 28-year-old man shows lesion with more than 75% T2 shortening with minimal high signal at anterior peripheral margin. 1766 AJR:184, June 2005

T2 Characteristics of Desmoplastic Fibroma of Bone osteolytic lesion with prominent T2 shortening on MR images make a diagnosis of intraosseous desmoid plausible. Acknowledgment We would like to pay special thanks to Scott Stacy of the University of Chicago for his assistance in providing two cases for this review. References 1. Jaffe HL. Tumors and tumorous conditions of the bones and joints. Philadelphia, PA: Lea and Febiger, 1958:298 303 2. Fornasico V, Pritzker KPH, Bridge JA. Desmoplastic fibroma of bone. In: Fletcher CDM, Unni KK, Merten SF, eds. The World Health Organization classification of tumours. Pathology and genetics of tumours of soft tissue and bone. Lyon: IARC Press, 2002:288 3. Taconis WK, Schütte HE, van der Heul RO. Desmoplastic fibroma of bone: a report of 18 cases. Skeletal Radiol 1994;23:283 288 4. Vanhoenacker FM, Hauben E, De Beuckeleer LH, Willemen D, Van Marck E, De Schepper AM. Desmoplastic fibroma of bone: MRI features. Skeletal Radiol 2000;29:171 175 5. Sundaram M, McGuire MH, Schajowicz F. Softtissue masses: histologic basis for decreased signal (short T2) on T2-weighted MR images. AJR 1987;148:1247 1250 6. Vandevenne JE, De Schepper AM, De Beuckeleer L, et al. New concepts in understanding evolution of desmoid tumors: MR imaging of 30 lesions. Eur Radiol 1997;7:1013 1019 7. Inwards CY, Unni KK, Beabout JW, Sim FH. Desmoplastic fibroma of bone: radiographic analysis. Cancer 1991;68:1978 1983 8. Crim JR, Gold RH, Mirra JM, Eckardt JJ, Bassett LW. Desmoplastic fibroma of bone: radiographic analysis. Radiology 1989;172: 827 832 9. Andresen KJ, Sundaram M, Unni KK, Sim FH. Imaging features of low-grade central osteosarcoma of the long bones and pelvis. Skeletal Radiol 2004;33:373 379 10. Kong KY, Kang HS, Jung HW, Kim JJ, Lee CK. MR findings of desmoplastic fibroma of the spine. A case report. Acta Radiol 2000;41:89 91 11. Juergens KU, Bullmann V, Link TM, Brinkschmidt C, Heindel W. Desmoplastic fibroma in the thoracic spine: an unusual localization of a rare primary bone tumor. Eur Radiol 2001;11: 273 275 12. Norris MA, Kaplan PA, Pathria M, Greenway G. Fibrous dysplasia: magnetic resonance imaging appearance at 1.5 Tesla. Clin Imaging 1990;14: 211 215 13. Aoki J, Tanikawa H, Ishii K, et al. MR findings indicative of hemosiderin in giant-cell tumor of bone: frequency, cause, and diagnostic significance. AJR 1996;166:145 148 14. White LM, Schweitzer ME, Khalili K, Howarth DJ, Wunder JS, Bell RS. MR imaging of primary lymphoma of bone: variability of T2-weighted signal intensity. AJR 1998;170:1243 1247 15. Sundaram M, Akduman I, White LM, McDonald DJ, Kandel R, Janney C. Primary leiomyosarcoma of bone. AJR 1999;172:771 776 The full text and images from the American Journal of Roentgenology may also be viewed online at www.arrs.org or www.ajronline.org. AJR:184, June 2005 1767