| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
1 Department of Radiology, University of Occupational and Environmental Health,
Iseigaoka 1-1, Yahatanisi-ku, Kitakyushu-shi 807-8555, Japan.
2 Department of Pathology and Oncology, University of Occupational and
Environmental Health, Yahatanisi-ku, Kitakyushu-shi 807-8555, Japan.
3 Department of Orthopedic Surgery, University of Occupational and Environmental
Health, Yahatanisi-ku, Kitakyushu-shi 807-8555, Japan.
Received July 1, 2002;
accepted after revision November 12, 2002.
Address correspondence to T. Ohguri.
Abstract
 Top Abstract IntroductionResultsDiscussionReferences |
|---|
MATERIALS AND METHODS. The MR images of 35 pathologically proven benign lipomas in 35 patients and 23 well-differentiated liposarcomas in 17 patients were retrospectively reviewed. T1-, T2-, and fat-suppressed T1-weighted images were obtained after administration of gadopentetate dimeglumine. Margins and internal characteristics revealed on the MR images and the degree of contrast enhancement of septa were evaluated. These MR imaging findings were compared for well-differentiated liposarcomas and benign lipomas.
RESULTS. Completely irregular margins were recognized only in benign lipomas with a pathologic diagnosis of infiltrating lipoma. All tumors without a recognizable nonadipose component were benign lipomas (p < 0.05). As for the well-differentiated liposarcomas, thick septa and nodular or patchy nonadipose components were present more frequently in deep and retroperitoneal lesions than in subcutaneous lesions (p < 0.01). No cases showed only thin septa in the deep lesions of well-differentiated liposarcoma, and all cases showed thick septa or nodular or patchy nonadipose components. The septa in well-differentiated liposarcomas enhanced more strongly than did those in benign lipomas. The septa showed no enhancement relative to muscle in 11 of 19 benign lipomas, whereas the septa showed moderate or marked enhancement in all well-differentiated liposarcomas (p < 0.01).
CONCLUSION. Careful assessment of margins and internal characteristics on MR imaging can be a useful aid in further distinguishing between biologically different benign lipoma and well-differentiated liposarcoma.
|
TopAbstractIntroductionResultsDiscussionReferences |
|---|
Materials and Methods
We retrospectively reviewed the records of 35 patients with 35 benign lipomas (17 men and 18 women; age range, 26-78 years; average age, 55 years) and 17 patients with 23 well-differentiated liposarcomas (11 men and six women; age range, 44-83 years; average age, 62.7 years) from 1991 to 2001. All patients underwent preoperative MR imaging and had their tumors excised at our institution. The benign lipomas were smaller than 3 cm (n = 7), 3-5 cm (n = 14), 6-10 cm (n = 12), and larger than 10 cm (n = 2); and the well-differentiated liposarcomas were smaller than 3 cm (n = 0), 3-5 cm (n = 4), 6-10 cm (n = 7), and larger than 10 cm (n = 12). The locations of the benign lipomas were subcutaneous (n = 19) and deep somatic (n = 16); and the locations of the well-differentiated liposarcomas were subcutaneous (n = 9), deep somatic (n = 9), and retroperitoneal (n = 5). The histopathologic diagnoses of the benign lipomas were lipomas (n = 26), infiltrating lipomas (n = 4), parosteal lipomas (n = 2), fibrolipomas (n = 2), and spindle cell lipoma (n = 1). The histopathologic subtypes of the well-differentiated liposarcomas were lipomalike (n = 19) and sclerosing (n = 4). All surgical specimens of the tumors were reviewed and diagnosed by two pathologists who were experienced in the diagnosis of bone and soft-tissue tumors.
MR imaging was performed with a 1.5-T super-conductive unit (VISART, Toshiba Medial Systems, Tokyo, Japan; Signa, General Electric Medial Systems, Milwaukee, WI). Slice thickness varied from 4 to 10 mm, matrix size was 320-224 x 256-160, and pulse sequences were spin-echo T1-weighted images (TR range/TE range, 450-600/15-20) and T2-weighted images (2000-4000/80-120). Fat-suppressed T1-weighted imaging was performed after administration of IV gadopentetate dimeglumine (Magnevist, Schering, Berlin, Germany) (0.1 mmol/kg of body weight) on 21 cases of benign lipoma and 10 cases of well-differentiated liposarcoma. The MR images were reviewed by two radiologists who were unaware of the histopathologic diagnoses. The final assessment was reached by consensus.
Margins, internal structures, and degrees of enhancement of septa after IV
administration of gadopentetate dimeglumine were analyzed and classified as
follows. Margins were defined as well-defined and smooth, partially irregular,
and completely irregular. Lesions with well-defined and smooth margins were
further divided into a uninodular or a multinodular mass independent of shape.
Internal structures were classified into five types on the basis of MR signal
intensity of the nonadipose components: type I, nonadipose component
unrecognizable; type II, only thin septa (
2 mm) with low signal intensity
detectable; type III, one or two thick septa (> 2 mm) with low signal
intensity detectable; type IV, three or more thick septa detectable; and type
V, nodular or patchy nonadipose component detectable
(Fig. 1). The relationship
between the location of tumors and the internal characteristics on MR imaging
was also evaluated. Because tumors with a completely irregular margin that
prominently infiltrated the surrounding muscle at any point could not be
classified into any one of these five types, they were excluded from this
evaluation. All such lesions were infiltrating lipomas.
|
The degree of enhancement of the septa after administration of gadopentetate dimeglumine was determined relative to muscle: decreased enhancement was considered as no enhancement, similar to moderate enhancement; and increased enhancement was considered as marked enhancement.
For all cases, both macroscopic and microscopic histologic findings of surgical specimens were available and were examined in comparison with the previously mentioned MR findings.
The Fisher's exact test was used for statistical analysis to determine whether the differences between lipomas and liposarcomas in terms of margins, internal structures (as evaluated on the basis of nonfatty components), and enhancement of septa on fat-suppressed T1-weighted images after administration of gadopentetate dimeglumine were statistically significant. The Fisher's exact test was also used to determine whether the internal structures of well-differentiated liposarcomas differed significantly on the basis of location (i.e., subcutaneous, deep, and retroperitoneal lesions).
|
TopAbstractIntroductionResultsDiscussionReferences |
|---|
|
|
|
The assessment of internal characteristics showed that all the type I tumors were benign lipomas (Fig. 3). Most type II tumors were benign lipomas, but two were well-differentiated liposarcomas (Fig. 4). The differences were significant (p < 0.05, p < 0.01, respectively). Seven benign lipomas and six well-differentiated liposarcomas were found to be type III; there was no statistical significance for type III (Figs. 5A, 5B). All the type IV tumors were well-differentiated liposarcomas (p < 0.001) (Figs. 6A, 6B, 6C, 6D). Type V tumors were found in both lipomas and liposarcomas. Of the three type V lipomas, two were parosteal lipomas and one was a spindle cell lipoma. The MR images of these parosteal lipomas clearly showed the lipomatous and osteochondromatous components. Of the well-differentiated liposarcomas, two deep lesions and all retroperitoneal lesions were type V (Fig. 7). In two well-differentiated liposarcomas of deep lesions and one spindle cell lipoma, the MR signal intensities of the nodular or patchy nonadipose components were low-intermediate or low relative to the muscle on T1- and T2-weighted images. The nodular components in these two well-differentiated liposarcomas histologically showed fibrous tissue and smooth muscle differentiation.
|
|
|
|
|
|
|
|
|
The relationship between the locations of tumors and their internal characteristics is shown in Table 3. For well-differentiated liposarcomas, thick septa and nodular or patchy nonadipose components were present more frequently in deep and retroperitoneal lesions than in subcutaneous lesions. Five of eight subcutaneous well-differentiated liposarcomas were type III, seven of 10 deep lesions were type IV, and all retroperitoneal lesions were type V (p < 0.01). Two well-differentiated liposarcomas with thin septa alone were located in the subcutaneous region, and no case showed thin septa alone in deep lesions.
|
All septa were hypointense on both T1- and T2-weighted images, but the septa of well-differentiated liposarcomas tended to be enhanced more prominently than those of lipomas on fat-suppressed T1-weighted images after administration of gadopentetate dimeglumine (Table 4). No enhancement of the septa was observed in 11 of 19 benign lipomas, but the septa in the well-differentiated liposarcomas showed moderate or marked enhancement. This difference was significant (p < 0.01). Six of eight well-differentiated liposarcomas showed marked enhancement that was seen in only one benign lipoma (p < 0.001). The well-differentiated liposarcomas histologically contained thick fibrous septa with some large and small or small blood vessels and vacuolated lipoblasts. Inflammatory cells and myxoid areas were frequently observed near the septa.
|
|
TopAbstractIntroductionResultsDiscussionReferences |
|---|
Our results concur with a recent report by Kransdorf et al. [11], in which the authors reported the distinguishing features of lipoma and well-differentiated liposarcoma and suggested that the risk of malignancy increases with the advanced age and with the sex (men have a higher rate of liposarcoma) of the patient and the increased lesion size. In the case of our subjects, the average age for patients with benign lipoma was 55 years and for those with well-differentiated liposarcoma, 62.7 years. Of the lesions larger than 10 cm, two were benign lipomas and 12 were well-differentiated liposarcomas. Well-differentiated liposarcomas were seen in 11 men and six women.
Matsumoto et al. [9] reported that an infiltrative nature, which is a general characteristic of a malignant tumor, indicates benignity and not malignancy in an intramuscular (infiltrating) lipoma. In our three cases of intramuscular (infiltrating) lipomas, the margins were completely irregular at all points where the neoplastic fatty tissue infiltrated and intermingled with the surrounding muscle tissue. Completely irregular margins were recognized only in infiltrating lipomas, and therefore they still could be easily distinguished from well-differentiated liposarcomas, although this finding was not statistically significant (p = 0.27) because of the small number of patients with infiltrating lipoma. Multinodular margins were frequently recognized in well-differentiated liposarcomas, and uninodular margins were seen in benign lipomas with statistical significance. However, it may not be advisable to rely on this finding alone because some cases overlapped.
Enzinger and Weiss [12] mentioned a tendency of well-differentiated liposarcoma to have more fibrous septa compared with lipoma, and they found that atypical cells or vacuolated lipoblasts admixed with fibroblastlike spindle cells are frequently situated in the septa surrounding irregularly sized lobules of fat. In our study, benign lipomas could be easily distinguished from well-differentiated liposarcomas when benign lipomas were completely composed of adipose tissue (p < 0.05), although nonadipose tissue was recognized in 25 of 35 benign tumors. Well-differentiated liposarcomas of the extremities recur in nearly half of patients, whereas the recurrence rate in the retroperitoneum approaches 100%. Approximately one third of patients die as a direct result of their disease. Although deep somatic soft-tissue lesions recur frequently, subcutaneous lesions are generally cured by limited excision [12, 13]. Dedifferentiation occurs most frequently in retroperitoneal liposarcomas and in deep somatic lesions, but dedifferentiation is rare in subcutaneous tumors. The location of a tumor strongly influences its biologic behavior. MR findings may reflect the site-dependent differences in the behavior of well-differentiated liposarcoma. In our study, thick septa were more prevalent in deep lesions than in subcutaneous lesions (p < 0.01). In deep lesions, no case showed thin septa alone. Hosono et al. [8] reported that lipoblasts, vessels, myxoid areas, and inflammatory cells in addition to the septa in well-differentiated liposarcoma may contribute to the prominent enhancement after administration of gadopentetate dimeglumine. In our study, the septa in well-differentiated liposarcomas were enhanced more prominently than in benign lipomas on fat-suppressed T1-weighted images after administration of gadopentetate dimeglumine. In addition, cases with septa that showed no enhancement were all benign lipomas (p < 0.01). The well-differentiated liposarcomas in our study contained thick fibrous septa with some large or small blood vessels; and vacuolated lipoblasts, inflammatory cells, and myxoid areas were frequently observed near the septa. When considering these observations, we found that an adipose tumor situated in a deep location with only thin septa showing no enhancement after administration of gadopentetate dimeglumine may be safely regarded as benign. Careful assessment of internal fatty tumors on MR imaging is thus useful in distinguishing between well-differentiated liposarcomas and lipomas and may contribute to a more accurate preoperative assessment for the surgical approach.
Fat-suppressed T1-weighted MR imaging was performed after IV administration of gadopentetate dimeglumine in six of seven benign lipomas in which a few thick septa had been recognized. Unlike well-differentiated liposarcomas, no marked enhancement of the septa could be seen in these cases, except one, after administration of gadopentetate dimeglumine. Therefore, it is likely that septa enhancement plays a more important role than septa thickness in differentiating benign lipoma from well-differentiated liposarcoma. Angiolipoma may be difficult to distinguish from well-differentiated liposarcoma by enhancement with gadolinium alone, but it often occurs in the forearm, usually has multiple lesions, and may be tender on palpation. These characteristics can be helpful in differentiating angiolipoma from other tumors. Although our cases of fibrolipoma and lipoma with myxoid change showed less enhancement than did muscle, the enhancement of these types of lipoma may be influenced by the vascular richness of internal structures.
Nodular or patchy nonadipose components were recognized in both benign lipomas and well-differentiated liposarcomas. Two cases of parosteal lipoma and one case of spindle cell lipoma showed these components. In two parosteal lipomas, MR imaging clearly showed the lipomatous and osteochondromatous components. A correct preoperative diagnosis of this rare tumor is possible if these characteristic features are confirmed on MR imaging. A spindle cell lipoma is a lipomatous mass in which primitive, benign collagen-forming spindle cells have either partially or totally replaced mature fat. Pleomorphic lipoma may be a variant of a spindle cell lipoma. Kransdorf et al. [5] found that areas of spindle cell proliferation within the fatty tumor show soft-tissue attenuation on CT, and as such, these tumors can mimic liposarcoma. The nodular components in our two cases of well-differentiated liposarcomas histologically showed fibrous tissue and smooth muscle differentiation. In two well-differentiated liposarcomas situated in deep locations and in one spindle cell lipoma, the MR signal intensities of the nodular or patchy nonadipose components that showed low-intermediate signal intensity or low signal intensity on T1- and T2-weighted images were not specific. Spindle cell or pleomorphic lipoma is usually encountered in men between the ages of 45 and 65 years and is most frequently located in the posterior neck and shoulder. Although spindle cell or pleomorphic lipoma shares the MR findings of well-differentiated liposarcomas, such clinical information may be of assistance in reaching an accurate diagnosis.
In conclusion, although some MR findings are shared by both benign lipomas and well-differentiated liposarcomas, MR imaging of the margins and internal characteristics is useful for the preoperative diagnosis of these tumors.
|
TopAbstractIntroductionResultsDiscussionReferences |
|---|
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
This article has been cited by other articles:
|
|
 |
|
  O. M. Navarro, E. E. Laffan, and B.-Y. Ngan Pediatric Soft-Tissue Tumors and Pseudo-tumors: MR Imaging Features with Pathologic Correlation: Part 1. Imaging Approach, Pseudotumors, Vascular Lesions, and Adipocytic Tumors RadioGraphics, May 1, 2009; 29(3): 887 - 906. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
W. D. Craig, J. C. Fanburg-Smith, L. R. Henry, R. Guerrero, and J. H Barton Fat-containing Lesions of the Retroperitoneum: Radiologic-Pathologic Correlation1 RadioGraphics, January 1, 2009; 29(1): 261 - 290. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 I-C Chiang, M-Y Jang, K-B Tsai, and T-J Hsieh Huge renal lipoma with prominent hypervascular non-adipose elements. Br. J. Radiol., October 1, 2006; 79(946): e148 - e151. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. D. Murphey, L. K. Arcara, and J. Fanburg-Smith From the Archives of the AFIP: Imaging of Musculoskeletal Liposarcoma with Radiologic-Pathologic Correlation RadioGraphics, September 1, 2005; 25(5): 1371 - 1395. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. D. Murphey, J. F. Carroll, D. J. Flemming, T. L. Pope, F. H. Gannon, and M. J. Kransdorf From the Archives of the AFIP: Benign Musculoskeletal Lipomatous Lesions RadioGraphics, September 1, 2004; 24(5): 1433 - 1466. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. M. Gaskin and C. A. Helms Lipomas, Lipoma Variants, and Well-Differentiated Liposarcomas (Atypical Lipomas): Results of MRI Evaluations of 126 Consecutive Fatty Masses Am. J. Roentgenol., March 1, 2004; 182(3): 733 - 739. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
