(Radiographics. 2000;20:1007-1019.)
© RSNA, 2000
Myxoid Liposarcoma: Appearance at MR Imaging with Histologic Correlation1
Mi-Sook Sung, MD,
Heong S. Kang, MD,
Jin S. Suh, MD,
Jung H. Lee, MD,
Jeong M. Park, MD,
Jee Y. Kim, MD and
Hae G. Lee, MD
1 From the Department of Radiology, Catholic University of Korea at Holy Family Hospital, Sosa-dong, Puchun, Kyunggido 420-717, Korea (M.S.S., J.M.P., J.Y.K., H.G.L.); the Department of Radiology, Seoul National University Hospital, Seoul, Korea (H.S.K.); the Department of Radiology, Yonsei University, Shinchon Severance Hospital, Seoul (J.S.S.); and the Department of Radiology, Korea Cancer Center, Seoul (J.H.L.). Presented as a scientific exhibit at the 1998 RSNA scientific assembly. Received April 8, 1999; revision requested May 6 and received July 2; accepted July 7. Address correspondence to M.S.S. (e-mail: mssung@clin.hfh.cuk.ac.kr).
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Abstract
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Although myxoid liposarcoma is a subtype of liposarcoma, it may be difficult to establish the correct diagnosis with magnetic resonance (MR) imaging due to the lack of fat signal intensity. Without the administration of gadolinium contrast material, the tumor may even mimic a cystic tumor. A spectrum of MR imaging abnormalities occur in myxoid liposarcoma, depending on the amount of fat and myxoid material, the degree of cellularity and vascularity, and the presence of necrosis. Most myxoid liposarcomas have lacy or linear, amorphous foci of fat. Some myxoid liposarcomas appear to be cystic at nonenhanced MR imaging, although they enhance like other solid masses at contrast material–enhanced MR imaging. The enhancing areas within the tumor represent increased cellularity and vascularity; the nonenhancing areas represent necrosis, reduced cellularity, and accumulated mucinous material. Gadolinium-enhanced imaging is important in differentiating myxoid liposarcoma from benign cystic tumors. Characterization of the tumor with MR imaging plays an important role in the management of myxoid liposarcoma.
Index Terms: Liposarcoma, 40.371 • Soft tissues, MR, 40.121411 • Soft tissues, neoplasms, 40.371 • Soft tissues, US, 40.12981
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Introduction
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Liposarcoma is the second most common of the adult soft-tissue sarcomas, accounting for 14%–18% of all soft-tissue sarcomas (1,2). Liposarcomas originate from primitive mesenchymal cells rather than from mature fat cells. At histologic analysis, they can be classified as well-differentiated, myxoid, pleomorphic, or round cell (3). The prognosis of patients with liposarcomas varies with the histologic subtype. The well-differentiated variant is considered a low-grade malignancy, whereas the pleomorphic and round cell types are regarded as highly malignant tumors with a tendency toward local recurrence and metastasis. The myxoid subtype has an intermediate prognosis. The histologic features, site, and size of a liposarcoma are the factors that influence its behavior and prognosis (1,3,4).
Myxoid liposarcoma is the second most common type of liposarcoma, representing 30%–40% of all liposarcomas in the extremities. Myxoid liposarcomas occur most commonly in the lower extremity, particularly the thigh (2). Other sites (in decreasing order of frequency) include the buttocks, retroperitoneum, trunk, ankle, proximal limb girdle, head and neck, and wrist. Myxoid liposarcomas occur in the intermuscular fascial planes or deep-seated areas. They are rarely found in the subcutaneous tissue. Most patients with these tumors are aged 18–67 years, with a mean age of 42 years. Patients with liposarcoma in the extremities are on the average 5–10 years younger than those with tumors in the retroperitoneum (3). The clinical presentation includes a large, slow-growing, painless mass. The mass is relatively soft and nontender at palpation.
At microscopic analysis, myxoid liposarcoma consists of a myxoid matrix, delicate arborizing vascular networks, and lipoblasts. Because the fat content is often less than 10%–25% of the tumor volume, magnetic resonance (MR) imaging may not show the typical features of a lipomatous tumor (4–6). A myxoid liposarcoma that contains abundant water can mimic a cystic lesion, producing diagnostic confusion (4,6,7). Myxoid liposarcomas must be differentiated from cystic lesions because the former can be limb threatening.
In this article, we describe the appearance of myxoid liposarcoma at nonenhanced and at gadolinium-enhanced MR imaging, discuss recurrent or multicentric tumors, and review the differential diagnosis.
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Appearance at Nonenhanced MR Imaging
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Typical Appearance
Myxoid liposarcomas exhibit low signal intensity on nonenhanced T1-weighted images and high signal intensity on T2-weighted images. At histologic analysis, myxoid liposarcomas consist of a myxoid matrix as the predominant component and small amounts of mature fat. These histologic characteristics account for the low signal intensity of the lesions on T1-weighted images. In contrast, lipomas and well-differentiated liposarcomas typically show high signal intensity secondary to the relatively high fat content (4–6).
On T1-weighted images, most myxoid liposarcomas (21 of 27 [78%] in our clinical experience) exhibit high-signal-intensity foci within a predominantly homogeneous low-signal-intensity mass (Fig 1). These foci represent fat within the tumor and usually appear lacy or linear and amorphous rather than solid (Fig 2). They demonstrate intermediate signal intensity and appear more prominent on T2-weighted images.
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Figure 1a. Myxoid liposarcoma with a typical appearance and homogeneous enhancement. (a) Sagittal T1-weighted MR image shows linear high-signal-intensity foci of fat within a predominantly low-signal-intensity mass. (b) Sagittal T2-weighted MR image shows foci of intermediate signal intensity within the high-signal-intensity mass. (c) Contrast material-enhanced sagittal T1-weighted MR image shows marked homogeneous enhancement throughout the mass. (d) Photomicrograph (original magnification, x100; hematoxylin-eosin stain) of the pathologic specimen shows a prominent plexiform capillary pattern, cellularity, an abundance of myxoid material, and lipoblasts.
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Figure 1b. Myxoid liposarcoma with a typical appearance and homogeneous enhancement. (a) Sagittal T1-weighted MR image shows linear high-signal-intensity foci of fat within a predominantly low-signal-intensity mass. (b) Sagittal T2-weighted MR image shows foci of intermediate signal intensity within the high-signal-intensity mass. (c) Contrast material-enhanced sagittal T1-weighted MR image shows marked homogeneous enhancement throughout the mass. (d) Photomicrograph (original magnification, x100; hematoxylin-eosin stain) of the pathologic specimen shows a prominent plexiform capillary pattern, cellularity, an abundance of myxoid material, and lipoblasts.
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Figure 1c. Myxoid liposarcoma with a typical appearance and homogeneous enhancement. (a) Sagittal T1-weighted MR image shows linear high-signal-intensity foci of fat within a predominantly low-signal-intensity mass. (b) Sagittal T2-weighted MR image shows foci of intermediate signal intensity within the high-signal-intensity mass. (c) Contrast material-enhanced sagittal T1-weighted MR image shows marked homogeneous enhancement throughout the mass. (d) Photomicrograph (original magnification, x100; hematoxylin-eosin stain) of the pathologic specimen shows a prominent plexiform capillary pattern, cellularity, an abundance of myxoid material, and lipoblasts.
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Figure 1d. Myxoid liposarcoma with a typical appearance and homogeneous enhancement. (a) Sagittal T1-weighted MR image shows linear high-signal-intensity foci of fat within a predominantly low-signal-intensity mass. (b) Sagittal T2-weighted MR image shows foci of intermediate signal intensity within the high-signal-intensity mass. (c) Contrast material-enhanced sagittal T1-weighted MR image shows marked homogeneous enhancement throughout the mass. (d) Photomicrograph (original magnification, x100; hematoxylin-eosin stain) of the pathologic specimen shows a prominent plexiform capillary pattern, cellularity, an abundance of myxoid material, and lipoblasts.
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Figure 2a. Myxoid liposarcoma with a typical appearance and heterogeneous enhancement. (a, b) Sagittal T1-weighted (a) and T2-weighted (b) MR images show lacy and amorphous foci of fat within a mass. (c) Gadolinium-enhanced sagittal T1-weighted MR image shows heterogeneous enhancement throughout the mass.
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Figure 2b. Myxoid liposarcoma with a typical appearance and heterogeneous enhancement. (a, b) Sagittal T1-weighted (a) and T2-weighted (b) MR images show lacy and amorphous foci of fat within a mass. (c) Gadolinium-enhanced sagittal T1-weighted MR image shows heterogeneous enhancement throughout the mass.
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Figure 2c. Myxoid liposarcoma with a typical appearance and heterogeneous enhancement. (a, b) Sagittal T1-weighted (a) and T2-weighted (b) MR images show lacy and amorphous foci of fat within a mass. (c) Gadolinium-enhanced sagittal T1-weighted MR image shows heterogeneous enhancement throughout the mass.
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At morphologic analysis, the mass is well defined. The lesion is frequently lobulated and may be multiloculated (Fig 3) or oval. Edema may be present in the soft tissue surrounding the tumor. There is no evidence of infiltration or invasion into adjacent structures.
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Figure 3a. Multiloculated myxoid liposarcoma. (a) Axial T1-weighted MR image shows lacy and amorphous high-signal-intensity foci of fat within a mass. The mass is multiloculated and located in the intramuscular and subcutaneous tissue. (b) Contrast-enhanced axial T1-weighted MR image shows heterogeneous enhancement.
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Figure 3b. Multiloculated myxoid liposarcoma. (a) Axial T1-weighted MR image shows lacy and amorphous high-signal-intensity foci of fat within a mass. The mass is multiloculated and located in the intramuscular and subcutaneous tissue. (b) Contrast-enhanced axial T1-weighted MR image shows heterogeneous enhancement.
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Cystic Appearance
Some myxoid liposarcomas may not exhibit the signal intensity typical of a fatty tumor and may instead appear as cystic masses on nonenhanced images (Fig 4). The absence of high-signal-intensity foci on T1-weighted images makes a myxoid liposarcoma indistinguishable from most other soft-tissue masses. In our clinical experience, nonenhanced MR imaging showed cystlike masses in six of 27 patients (22%). Jelinek et al (4) reported a similar prevalence of myxoid liposarcoma with a cystic appearance at MR imaging.
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Figure 4a. Myxoid liposarcoma with a cystic appearance at nonenhanced MR imaging. (a, b) Coronal T1-weighted (a) and axial T2-weighted (b) MR images show a well-defined cystlike lesion in the subcutaneous tissue (arrows). (c) Gadolinium-enhanced coronal T1-weighted MR image shows heterogeneous enhancement with a line of demarcation between the enhancing and nonenhancing regions (arrowheads). (d) Longitudinal US scan shows a complex, hypoechoic mass that does not meet the criteria for a simple cyst. (e) Photomicrograph (original magnification, x100; hematoxylin-eosin stain) shows a line of demarcation (arrows) between an area of compact cellularity with a typical vascular and myxoid pattern (left side of image) and an area of reduced cellularity (right side of image).
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Figure 4b. Myxoid liposarcoma with a cystic appearance at nonenhanced MR imaging. (a, b) Coronal T1-weighted (a) and axial T2-weighted (b) MR images show a well-defined cystlike lesion in the subcutaneous tissue (arrows). (c) Gadolinium-enhanced coronal T1-weighted MR image shows heterogeneous enhancement with a line of demarcation between the enhancing and nonenhancing regions (arrowheads). (d) Longitudinal US scan shows a complex, hypoechoic mass that does not meet the criteria for a simple cyst. (e) Photomicrograph (original magnification, x100; hematoxylin-eosin stain) shows a line of demarcation (arrows) between an area of compact cellularity with a typical vascular and myxoid pattern (left side of image) and an area of reduced cellularity (right side of image).
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Figure 4c. Myxoid liposarcoma with a cystic appearance at nonenhanced MR imaging. (a, b) Coronal T1-weighted (a) and axial T2-weighted (b) MR images show a well-defined cystlike lesion in the subcutaneous tissue (arrows). (c) Gadolinium-enhanced coronal T1-weighted MR image shows heterogeneous enhancement with a line of demarcation between the enhancing and nonenhancing regions (arrowheads). (d) Longitudinal US scan shows a complex, hypoechoic mass that does not meet the criteria for a simple cyst. (e) Photomicrograph (original magnification, x100; hematoxylin-eosin stain) shows a line of demarcation (arrows) between an area of compact cellularity with a typical vascular and myxoid pattern (left side of image) and an area of reduced cellularity (right side of image).
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Figure 4d. Myxoid liposarcoma with a cystic appearance at nonenhanced MR imaging. (a, b) Coronal T1-weighted (a) and axial T2-weighted (b) MR images show a well-defined cystlike lesion in the subcutaneous tissue (arrows). (c) Gadolinium-enhanced coronal T1-weighted MR image shows heterogeneous enhancement with a line of demarcation between the enhancing and nonenhancing regions (arrowheads). (d) Longitudinal US scan shows a complex, hypoechoic mass that does not meet the criteria for a simple cyst. (e) Photomicrograph (original magnification, x100; hematoxylin-eosin stain) shows a line of demarcation (arrows) between an area of compact cellularity with a typical vascular and myxoid pattern (left side of image) and an area of reduced cellularity (right side of image).
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Figure 4e. Myxoid liposarcoma with a cystic appearance at nonenhanced MR imaging. (a, b) Coronal T1-weighted (a) and axial T2-weighted (b) MR images show a well-defined cystlike lesion in the subcutaneous tissue (arrows). (c) Gadolinium-enhanced coronal T1-weighted MR image shows heterogeneous enhancement with a line of demarcation between the enhancing and nonenhancing regions (arrowheads). (d) Longitudinal US scan shows a complex, hypoechoic mass that does not meet the criteria for a simple cyst. (e) Photomicrograph (original magnification, x100; hematoxylin-eosin stain) shows a line of demarcation (arrows) between an area of compact cellularity with a typical vascular and myxoid pattern (left side of image) and an area of reduced cellularity (right side of image).
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US is useful in differentiating solid masses from cystic lesions. It has become the primary imaging modality for evaluation of soft-tissue masses accessible to US. When myxoid liposarcomas have a purely cystic appearance at MR imaging, both contrast-enhanced MR imaging and US are useful in the differential diagnosis. Myxoid liposarcomas with a cystic appearance at MR imaging usually appear as complex, hypoechoic masses that do not meet the criteria for a simple cyst at US (Fig 4).
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Appearance at Gadolinium-enhanced MR Imaging
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Enhancement Patterns
Myxoid liposarcoma can mimic a fluid-filled cyst at T2-weighted imaging because of their similar appearances: very high signal intensity and clear demarcation of the tumor with homogeneous signal intensity. Correct diagnosis is important because misdiagnosis of the tumor has an important therapeutic implication. Contrast-enhanced MR imaging is useful in distinguishing cystic or necrotic lesions from solid, cellular lesions (8,9).
In our clinical experience, all but one of 27 myxoid liposarcomas appeared as solid masses with varying patterns of enhancement at gadolinium-enhanced MR imaging. The tumors that had a cystic appearance at nonenhanced imaging appeared as solid masses with intense enhancement. However, Beltran et al (9) reported that myxoid tumors including intramuscular myxoma, myxoid liposarcoma, and hyaline cartilage lesions showed little enhancement at gadolinium-enhanced MR imaging.
The enhancement patterns of the myxoid liposarcomas could be classified into three groups: homogeneous (total enhancement), heterogeneous (partial enhancement), and no enhancement. In the tumors with heterogeneous enhancement, the enhancement was intense, involving more than 80% of the tumor volume in most of our patients. The tumors in this group showed gradual enhancement over time following administration of gadolinium contrast material. Kim et al (10) reported a similar pattern of enhancement in myxoid liposarcomas. In patients with multiloculated masses, enhancement is heterogeneous, with areas of no enhancement and areas of nearly complete enhancement (Fig 5).
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Figure 5a. Biloculated liposarcoma with a peculiar enhancement pattern. (a) Axial T1-weighted MR image shows a biloculated, low-signal-intensity mass in the deep soft tissue of the distal thigh (arrows). (b, c) Gadolinium-enhanced coronal T1-weighted MR images show no enhancement of the anterior portion of the mass (arrows in b) and nearly complete enhancement of the posterior portion except for the center (arrows in c).
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Figure 5b. Biloculated liposarcoma with a peculiar enhancement pattern. (a) Axial T1-weighted MR image shows a biloculated, low-signal-intensity mass in the deep soft tissue of the distal thigh (arrows). (b, c) Gadolinium-enhanced coronal T1-weighted MR images show no enhancement of the anterior portion of the mass (arrows in b) and nearly complete enhancement of the posterior portion except for the center (arrows in c).
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Figure 5c. Biloculated liposarcoma with a peculiar enhancement pattern. (a) Axial T1-weighted MR image shows a biloculated, low-signal-intensity mass in the deep soft tissue of the distal thigh (arrows). (b, c) Gadolinium-enhanced coronal T1-weighted MR images show no enhancement of the anterior portion of the mass (arrows in b) and nearly complete enhancement of the posterior portion except for the center (arrows in c).
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Correlation between MR Imaging and Histologic Features
Gadolinium-enhanced MR imaging plays an important role in differentiating cystic or necrotic areas from solid, cellular regions. Gadolinium-enhanced MR images demonstrate the overall vascularity and enhancement pattern of the tumor (8,9). The enhancing areas of the tumor generally correlate well with areas of tissue vascularity and increased cellular components (6, 10,11). The enhancement patterns seen on contrast-enhanced MR images depend on the degree of cellularity and vascularity and the presence of necrosis (Figs 1, 4, 6). Tumors with a homogeneous enhancement pattern have a prominent plexiform capillary pattern, increased cellularity, and abundant myxoid substance (Fig 1). In tumors with heterogeneous enhancement, the enhancement pattern is variable. These tumors consist of two distinct zones (Fig 4). One zone has compact cellularity with a prominent capillary network and a myxoid pattern; this zone represents the enhancing areas. The other zone contains necrosis with or without hemorrhage, mucinous material, and a less cellular myxoid portion without capillary networks; this zone represents the nonenhancing areas (Fig 6). Tumors with a myxoid component of less than 65% tend to lack a large fatty component but instead have a large necrotic area.
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Figure 6a. Nonenhancing myxoid liposarcoma with a misleadingly benign appearance. (a) Axial T2-weighted MR image shows a well-defined high-signal-intensity mass adjacent to the femur. (b) Axial T1-weighted MR image shows subtle high-signal-intensity septa of fat within the predominantly low-signal-intensity mass (arrows). (c) Gadolinium-enhanced axial T1-weighted MR image shows no enhancement of the mass (arrows). (d) Photomicrograph (original magnification, x100; hematoxylin-eosin stain) shows reduced cellularity. (e) Photomicrograph (original magnification, x40; hematoxylin-eosin stain) shows hemorrhagic necrosis.
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Figure 6b. Nonenhancing myxoid liposarcoma with a misleadingly benign appearance. (a) Axial T2-weighted MR image shows a well-defined high-signal-intensity mass adjacent to the femur. (b) Axial T1-weighted MR image shows subtle high-signal-intensity septa of fat within the predominantly low-signal-intensity mass (arrows). (c) Gadolinium-enhanced axial T1-weighted MR image shows no enhancement of the mass (arrows). (d) Photomicrograph (original magnification, x100; hematoxylin-eosin stain) shows reduced cellularity. (e) Photomicrograph (original magnification, x40; hematoxylin-eosin stain) shows hemorrhagic necrosis.
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Figure 6c. Nonenhancing myxoid liposarcoma with a misleadingly benign appearance. (a) Axial T2-weighted MR image shows a well-defined high-signal-intensity mass adjacent to the femur. (b) Axial T1-weighted MR image shows subtle high-signal-intensity septa of fat within the predominantly low-signal-intensity mass (arrows). (c) Gadolinium-enhanced axial T1-weighted MR image shows no enhancement of the mass (arrows). (d) Photomicrograph (original magnification, x100; hematoxylin-eosin stain) shows reduced cellularity. (e) Photomicrograph (original magnification, x40; hematoxylin-eosin stain) shows hemorrhagic necrosis.
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Figure 6d. Nonenhancing myxoid liposarcoma with a misleadingly benign appearance. (a) Axial T2-weighted MR image shows a well-defined high-signal-intensity mass adjacent to the femur. (b) Axial T1-weighted MR image shows subtle high-signal-intensity septa of fat within the predominantly low-signal-intensity mass (arrows). (c) Gadolinium-enhanced axial T1-weighted MR image shows no enhancement of the mass (arrows). (d) Photomicrograph (original magnification, x100; hematoxylin-eosin stain) shows reduced cellularity. (e) Photomicrograph (original magnification, x40; hematoxylin-eosin stain) shows hemorrhagic necrosis.
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Figure 6e. Nonenhancing myxoid liposarcoma with a misleadingly benign appearance. (a) Axial T2-weighted MR image shows a well-defined high-signal-intensity mass adjacent to the femur. (b) Axial T1-weighted MR image shows subtle high-signal-intensity septa of fat within the predominantly low-signal-intensity mass (arrows). (c) Gadolinium-enhanced axial T1-weighted MR image shows no enhancement of the mass (arrows). (d) Photomicrograph (original magnification, x100; hematoxylin-eosin stain) shows reduced cellularity. (e) Photomicrograph (original magnification, x40; hematoxylin-eosin stain) shows hemorrhagic necrosis.
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Some liposarcomas consist of multiple histologic subtypes within the same lesion (4,10). In this setting, the signal intensity throughout the lesion can vary depending on the combination of histologic subtypes. In our clinical experience, three of 27 patients (11%) had liposarcoma of the well-differentiated subtype as a minor component of their tumor. The tumors had the typical histologic features of myxoid liposarcoma with small areas of the well-differentiated subtype. These findings correlated well with the MR imaging findings (Fig 7).
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Figure 7a. Combination of myxoid and well-differentiated liposarcoma. (a) Axial T1-weighted MR image shows a predominantly low-signal-intensity mass with faint high-signal-intensity foci occupying the right gluteus maximus muscle. A focal area of the well-differentiated subtype appears as a minor nodular component with signal intensity equal to that of fat (arrows). (b) Gadolinium-enhanced axial T1-weighted MR image shows heterogeneous enhancement of only the myxoid subtype. (c) Photomicrograph (original magnification, x100; hematoxylin-eosin stain) shows a sharply defined border (arrows) between the well-differentiated subtype (left side of image) and the myxoid subtype (right side of image).
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Figure 7b. Combination of myxoid and well-differentiated liposarcoma. (a) Axial T1-weighted MR image shows a predominantly low-signal-intensity mass with faint high-signal-intensity foci occupying the right gluteus maximus muscle. A focal area of the well-differentiated subtype appears as a minor nodular component with signal intensity equal to that of fat (arrows). (b) Gadolinium-enhanced axial T1-weighted MR image shows heterogeneous enhancement of only the myxoid subtype. (c) Photomicrograph (original magnification, x100; hematoxylin-eosin stain) shows a sharply defined border (arrows) between the well-differentiated subtype (left side of image) and the myxoid subtype (right side of image).
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Figure 7c. Combination of myxoid and well-differentiated liposarcoma. (a) Axial T1-weighted MR image shows a predominantly low-signal-intensity mass with faint high-signal-intensity foci occupying the right gluteus maximus muscle. A focal area of the well-differentiated subtype appears as a minor nodular component with signal intensity equal to that of fat (arrows). (b) Gadolinium-enhanced axial T1-weighted MR image shows heterogeneous enhancement of only the myxoid subtype. (c) Photomicrograph (original magnification, x100; hematoxylin-eosin stain) shows a sharply defined border (arrows) between the well-differentiated subtype (left side of image) and the myxoid subtype (right side of image).
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Recurrent or Multicentric Tumors
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The MR imaging findings of recurrent myxoid liposarcomas are similar to those of the primary tumors. Postoperative hygromas and seromas usually appear as homogeneous cystic lesions on T1- and T2-weighted images (12,13). Recurrent myxoid liposarcomas may appear as cystic lesions on nonenhanced images (Fig 8). Knowledge of the histologic features of the original tumor is useful in differential diagnosis of recurrent tumor versus postoperative changes (8). Typically, recurrent tumors show enhancement 1–3 minutes after administration of gadolinium contrast material (Fig 8), whereas hygromas and seromas do not enhance (Fig 9), thus allowing differentiation between a recurrent tumor and a hygroma or seroma.
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Figure 8a. Recurrent myxoid liposarcoma with a cystic appearance. (a, b) Axial T1-weighted (a) and T2-weighted (b) MR images show a homogeneous, cystlike mass in the intermuscular tissue (arrowheads). The mass had recurred 4 years after excision. (c) Gadolinium-enhanced axial fat-suppressed MR image shows that the lesion is solid with homogeneous enhancement (arrowheads).
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Figure 8b. Recurrent myxoid liposarcoma with a cystic appearance. (a, b) Axial T1-weighted (a) and T2-weighted (b) MR images show a homogeneous, cystlike mass in the intermuscular tissue (arrowheads). The mass had recurred 4 years after excision. (c) Gadolinium-enhanced axial fat-suppressed MR image shows that the lesion is solid with homogeneous enhancement (arrowheads).
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Figure 8c. Recurrent myxoid liposarcoma with a cystic appearance. (a, b) Axial T1-weighted (a) and T2-weighted (b) MR images show a homogeneous, cystlike mass in the intermuscular tissue (arrowheads). The mass had recurred 4 years after excision. (c) Gadolinium-enhanced axial fat-suppressed MR image shows that the lesion is solid with homogeneous enhancement (arrowheads).
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Figure 9a. Seroma. (a) Axial T2-weighted MR image shows a homogeneous, high-signal-intensity lesion within a muscle of the thigh (arrows). Disruption of other thigh muscles is also seen. (b) Gadolinium-enhanced axial T1-weighted MR image shows only rim enhancement (arrows).
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Figure 9b. Seroma. (a) Axial T2-weighted MR image shows a homogeneous, high-signal-intensity lesion within a muscle of the thigh (arrows). Disruption of other thigh muscles is also seen. (b) Gadolinium-enhanced axial T1-weighted MR image shows only rim enhancement (arrows).
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Liposarcomas may be multicentric, with involvement of two or more anatomic sites. In 10% of patients with primary liposarcomas of the thigh, a second liposarcoma occurs in the retroperitoneum 2 or more years after removal of the primary tumor (Fig 10). Most of these tumors are of the myxoid type (3). In one patient with a liposarcoma of the thigh (Fig 7), the lesion metastasized to the spine and right chest wall 1 year after resection of the primary lesion.
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Figure 10a. Multicentric myxoid liposarcoma. (a) Gadolinium-enhanced axial T1-weighted MR image shows a heterogeneously enhancing mass in the thigh (arrows). (b) Gadolinium-enhanced sagittal T1-weighted MR image shows a focal area of enhancement within a predominantly low-signal-intensity mass in the retroperitoneum. The mass represented a second myxoid liposarcoma, which occurred 2 years after the initial surgery.
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Figure 10b. Multicentric myxoid liposarcoma. (a) Gadolinium-enhanced axial T1-weighted MR image shows a heterogeneously enhancing mass in the thigh (arrows). (b) Gadolinium-enhanced sagittal T1-weighted MR image shows a focal area of enhancement within a predominantly low-signal-intensity mass in the retroperitoneum. The mass represented a second myxoid liposarcoma, which occurred 2 years after the initial surgery.
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Differential Diagnosis
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Many benign and malignant soft-tissue tumors contain myxoid tissue. Such tumors include myxoid liposarcoma, extraskeletal myxoid chondrosarcoma, intramuscular myxoma, ganglion, and myxoid malignant fibrous histiocytoma (14). Unlike most malignant tumors, malignant tumors containing myxoid tissue tend to be well-defined and homogeneous. Any lesion consisting of edema, an extracellular matrix with a high level of mucopolysaccharide, hyaline cartilage content, and necrosis may appear as a cystic mass (15).
Extraskeletal Myxoid Chondrosarcoma
Myxoid chondrosarcomas are typically isointense to muscle on T1-weighted images and hyperintense on T2-weighted images. Heterogeneous enhancement is usually observed on contrast-enhanced images (Fig 11) (16). Contrast-enhanced images may show rings and arcs, which reflect the typical lobulated growth pattern of cartilaginous tumors of bone (17).
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Figure 11a. Extraskeletal myxoid chondrosarcoma. (a) Axial T1-weighted MR image shows a well-defined, lobulated, low-signal-intensity mass in the right gluteus maximus muscle (arrows). (b) Axial T2-weighted MR image shows that the mass has heterogeneous high signal intensity (arrows). (c) Contrast-enhanced axial T1-weighted MR image shows heterogeneous enhancement of the mass (arrows). c. Contrast-enhanced axial T1-weighted MR image shows heterogeneous enhancement of the mass (arrows).
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Figure 11b. Extraskeletal myxoid chondrosarcoma. (a) Axial T1-weighted MR image shows a well-defined, lobulated, low-signal-intensity mass in the right gluteus maximus muscle (arrows). (b) Axial T2-weighted MR image shows that the mass has heterogeneous high signal intensity (arrows). (c) Contrast-enhanced axial T1-weighted MR image shows heterogeneous enhancement of the mass (arrows). c. Contrast-enhanced axial T1-weighted MR image shows heterogeneous enhancement of the mass (arrows).
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Figure 11c. Extraskeletal myxoid chondrosarcoma. (a) Axial T1-weighted MR image shows a well-defined, lobulated, low-signal-intensity mass in the right gluteus maximus muscle (arrows). (b) Axial T2-weighted MR image shows that the mass has heterogeneous high signal intensity (arrows). (c) Contrast-enhanced axial T1-weighted MR image shows heterogeneous enhancement of the mass (arrows). c. Contrast-enhanced axial T1-weighted MR image shows heterogeneous enhancement of the mass (arrows).
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Intramuscular Myxoma
Intramuscular myxomas may occur in patients with fibrous dysplasia of bone (18). At MR imaging, myxoma appears as a well-defined mass with prolonged T1 and T2 that mimics a cyst on nonenhanced images (Fig 12). Heterogeneous enhancement is usually seen with varying patterns including peripheral, peripheral-nodular, and septal; these patterns were observed on 29% of computed tomographic scans and 100% of MR images in one study (19). Because of the variable and often complex components, differentiation of myxoma from myxoid liposarcoma may be difficult. However, myxoid liposarcoma has two distinct features that help differentiate it from myxoma. First, myxoid liposarcomas show intense enhancement of 65%–100% of the tumor volume in most cases (24 of 27 [89%] in our clinical experience), including those cases with a cystic appearance on nonenhanced images. Second, the high signal intensity from fatty foci on T1-weighted images is quite characteristic.
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Figure 12a. Intramuscular myxoma. (a, b) Sagittal T1-weighted (a) and T2-weighted (b) MR images show a well-defined, cystic, intramuscular mass (arrows). (c) Gadolinium-enhanced sagittal T1-weighted MR image shows heterogeneous enhancement throughout the mass (arrows).
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Figure 12b. Intramuscular myxoma. (a, b) Sagittal T1-weighted (a) and T2-weighted (b) MR images show a well-defined, cystic, intramuscular mass (arrows). (c) Gadolinium-enhanced sagittal T1-weighted MR image shows heterogeneous enhancement throughout the mass (arrows).
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Figure 12c. Intramuscular myxoma. (a, b) Sagittal T1-weighted (a) and T2-weighted (b) MR images show a well-defined, cystic, intramuscular mass (arrows). (c) Gadolinium-enhanced sagittal T1-weighted MR image shows heterogeneous enhancement throughout the mass (arrows).
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Ganglion
Ganglia occur most frequently along tendinous sheaths and in juxtaarticular locations; they occur uncommonly in muscle bundles (20). The MR imaging appearance of ganglion is similar to that of other cysts. No enhancement or peripheral enhancement is observed on gadolinium-enhanced images (Fig 13). However, ganglia are often septated, with smaller capsular cysts budding from the main cyst and dissecting along fascial planes. With MR imaging, one can easily establish the diagnosis of ganglion occurring in the typical locations.
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Figure 13a. Ganglion within a muscle bundle. (a) Coronal T1-weighted MR image shows a lobulated, septated, hypointense mass (arrows). (b) Coronal T2-weighted MR image shows the mass as hyperintense. (c) Gadolinium-enhanced coronal T1-weighted MR image shows thick peripheral enhancement.
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Figure 13b. Ganglion within a muscle bundle. (a) Coronal T1-weighted MR image shows a lobulated, septated, hypointense mass (arrows). (b) Coronal T2-weighted MR image shows the mass as hyperintense. (c) Gadolinium-enhanced coronal T1-weighted MR image shows thick peripheral enhancement.
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Figure 13c. Ganglion within a muscle bundle. (a) Coronal T1-weighted MR image shows a lobulated, septated, hypointense mass (arrows). (b) Coronal T2-weighted MR image shows the mass as hyperintense. (c) Gadolinium-enhanced coronal T1-weighted MR image shows thick peripheral enhancement.
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MR imaging plays an important role in evaluation of patients with cystic lesions of the extremities including epidermoid cyst, synovial cyst, bursitis, seroma, lymphocele, abscess, posttraumatic hematoma, and parasitic infestation. Differentiation between cystic lesions and soft-tissue masses with a cystic appearance is usually possible with contrast-enhanced MR imaging.
Epidermoid Cyst
Epidermoid cysts are usually found in the subcutaneous tissue (21). These cysts most often show the signal intensity characteristics of a simple cyst. No enhancement is observed at gadolinium-enhanced imaging (Fig 14). The signal intensity on T1-weighted images may be variable and depends on the nature of the keratin in the cyst and the amount of sebaceous lipid. The presence of intracystic hypointense debris on T2-weighted images helps differentiate epidermoid cysts from other cystic lesions.
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Figure 14a. Epidermoid cyst. (a) Coronal T1-weighted MR image shows a well-defined, homogeneous, low-signal-intensity mass in the perineal region. (b) Coronal T2-weighted MR image shows the mass as hyperintense. (c) Gadolinium-enhanced coronal T1-weighted MR image shows no enhancement of the mass.
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Figure 14b. Epidermoid cyst. (a) Coronal T1-weighted MR image shows a well-defined, homogeneous, low-signal-intensity mass in the perineal region. (b) Coronal T2-weighted MR image shows the mass as hyperintense. (c) Gadolinium-enhanced coronal T1-weighted MR image shows no enhancement of the mass.
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Figure 14c. Epidermoid cyst. (a) Coronal T1-weighted MR image shows a well-defined, homogeneous, low-signal-intensity mass in the perineal region. (b) Coronal T2-weighted MR image shows the mass as hyperintense. (c) Gadolinium-enhanced coronal T1-weighted MR image shows no enhancement of the mass.
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Bursitis
Accumulation of fluid in the bursal cavities may lead to soft-tissue masses. The commonly known types of bursitis include prepatellar, anserine, iliopsoas, trochanteric, bicipital, and cubital. These lesions are easily recognized because of their typical anatomic locations.
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Conclusions
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A spectrum of MR imaging features occur in myxoid liposarcomas of the soft tissue. These variable abnormalities are due to several factors. One factor is the fat content of the tumor. Other factors include the amount of myxoid material, the degree of cellularity and vascularity, and the presence of necrosis in the tumor. Most myxoid liposarcomas demonstrate lacy or linear, amorphous foci of fat; however, some tumors appear as a cystic lesion due to lack of fat content. Tumors with increased cellularity and vascularity tend to enhance on contrast-enhanced images, whereas tumors with necrosis, hypocellularity, and an accumulation of mucinous material tend not to enhance. Gadolinium-enhanced imaging can be helpful in differentiating myxoid liposarcomas from benign cystic tumors and in directing appropriate therapy.
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References
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Abstract
Introduction
