| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
1 Department of Radiology, Mayo Clinic, 4500 San Pablo Rd., Jacksonville, FL
32224-3899.
2 Department of Pathology, Mayo Clinic, Jacksonville, FL 32224-3899.
3 Department of Orthopedic Surgery, Mayo Clinic, Jacksonville, FL
32224-3899.
4 Department of Orthopedic Surgery, Medical College of Virginia, Virginia
Commonwealth University, 1200 E. Broad St., P. O. Box 980153, Richmond, VA
23298.
Received September 17, 2001;
accepted after revision October 30, 2001.
Address correspondence to M. J. Kransdorf.
Abstract
 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
MATERIALS AND MATERIALS. We retrospectively reviewed the MR imaging features of 20 patients with intramuscular myxoma. Clinical assessment included the age and sex of the patient and location of the tumor. Radiologic evaluation included the lesion size and shape, border definition, signal on T1- and T2-weighted or fluid-sensitive MR sequences, enhancement pattern, presence or absence of a fat rind, and presence or absence of increased signal in the adjacent muscle on T2-weighted or fluid-sensitive MR sequences.
RESULTS. The mean age of patients presenting with intramuscular myxoma was 61 years (range, 15-85 years; median, 64 years). The mean lesion size was 6.9 cm (range, 3-17 cm; median, 6.3 cm). A peritumoral fat rind was present in 13 of the patients (65%) with myxoma, and an increased signal in the adjacent muscle on fluid-sensitive sequences was present in 11 patients (55%). Intramuscular myxomas were homogeneously low in signal intensity on T1-weighted MR sequences in 19 patients (95%), with all lesions showing a high signal intensity on T2-weighted or fluid-sensitive MR sequences. Twelve of the myxomas had well-defined borders, and eight had borders that were partially ill defined. Of the 11 lesions imaged after gadolinium administration, six (55%) showed intense heterogeneous enhancement.
CONCLUSION. Findings of a mass that on MR images shows a perilesional fat rind, the signal intensity of fluid, and an increased signal in the adjacent muscle on T2-weighted or fluid-sensitive MR sequences are strongly suggestive of intramuscular myxoma. The degree of lesion enhancement varies but is most frequently intense and heterogeneous. Although the recognition of these features likely will not obviate biopsy of any individual lesion, it will allow more accurate prebiopsy diagnosis and preoperative planning.
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
The intramuscular myxoma is of particular interest to radiologists because it may have imaging features similar to other myxoid lesions, especially the myxoid liposarcoma. If a myxoid liposarcoma is in an intramuscular location and has a predominantly myxoid morphology (the so-called cystic appearance), the two lesions may be strikingly similar in appearance. The similarity of these lesions extends to the gross and histologic appearances as well, and differentiating between the two may be difficult [3]. Making this differentiation has major implications because intramuscular myxoma has a benign clinical course, with no tendency to recur or metastasize [4, 5]. We retrospectively reviewed our experience with intramuscular myxoma to identify the MR imaging characteristics of this lesion.
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
The MR imaging planes, sequences, and field strengths varied because of the nature of the study groups. All patients included in the study had at least one T1-weighted MR sequence and either a T2-weighted or fluid-sensitive MR sequence. Eleven of the 20 patients with myxoma also had IV gadolinium-enhanced images. Clinical assessment included the age and sex of each patient and the location of the tumor.
The radiologic evaluation included lesion size in centimeters (largest diameter), shape (spherical, ovoid, or lobulated), and border definition (well defined, partially ill defined, or wholly ill defined). Lesions were assessed on T1-weighted MR images relative to skeletal muscle as homogeneously low in signal intensity or low in signal intensity with areas of intermediate signal. On T2-weighted MR images, a signal intensity similar to that of fluid was designated as high, whereas a signal intensity similar to that of fat was considered intermediate. Signal intensity on fat-suppressed T2-weighted turbo spin-echo and short tau inversion recovery images was more difficult to grade, but lesions were considered high in signal intensity if their signal intensity was similar to that of fluid. The appearance of lesions was classified as homogeneous with high signal intensity, homogeneous with high signal intensity and low- or intermediate-signal septal components, homogeneous with high signal intensity and low- or intermediate-signal nodular components, or heterogeneous with both septal and nodular components. The presence or absence of gadolinium enhancement was noted. If such enhancement was present, it was characterized as homogeneous or heterogeneous.
The margin of the lesion was assessed for the presence or absence of a rind of fat at the interface between the lesion and muscle on T1-weighted MR images, and the presence or absence of increased signal in the skeletal muscle adjacent to the lesion on T2-weighted or fluid-sensitive MR sequences. In addition, we compared the reliability of the last two signs as tools in successfully distinguishing between an intramuscular myxoma and an intramuscular myxoid liposarcoma, the lesion with which a myxoma is most likely to be confused. To assess this reliability, we compared findings of the study group with those of a control group of 12 patients with intramuscular myxoid liposarcomas using the Wilcoxon's rank sum test for continuous variables and the chi-square test for categorized variables. Logistic regression was used to test for the influence of the study variables after adjusting for age and sex differences between the groups. The final multivariate logistic model was built using a stepwise selection method. We used a software package (SAS Institute, Cary, NC) for data analysis. A p value of 0.05 was considered statistically significant. The institutional review board approved our study.
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Twelve of the myxomas had well-defined borders (Fig. 1A,1B,1C,1D), and eight had partially ill-defined borders (Fig. 2A,2B,2C,2D,2E,2F). We found that imaging planes along the longitudinal axis of the involved muscle yielded the most information regarding lesion borders and conspicuity of signal differences between the lesions and the adjacent muscle. Lesions were most commonly ovoid (13/20; 65%) or less commonly lobulated (6/20; 30%); one lesion was spherical (5%).
|
|
|
|
|
|
|
|
|
|
All lesions showed a fluidlike signal intensity. Most of the lesions (19/20; 95%) were of homogeneously low signal intensity on T1-weighted MR sequences (Fig. 1A,1B,1C,1D). One lesion (5%) was of heterogeneously low signal intensity with poorly defined areas of intermediate signal intensity. The myxomas, similar to other myxoid lesions, all showed high signal on T2-weighted or fluid-sensitive MR sequences. Most lesions (13/20; 65%) showed associated peripheral linear regions of intermediate signal intensity (designated as a septal pattern). Four lesions (20%) were of homogeneously high signal intensity, and three (15%) showed a nodular septal pattern (Fig. 3A,3B). Although enhancement patterns varied, heterogeneous enhancement (Fig. 1A,1B,1C,1D) was seen in 55% (6/11) of the lesions in patients with myxomas who received gadolinium contrast material.
|
|
A peritumoral fat rind was found in 13 of the patients with myxoma (Figs. 1A,1B,1C,1D and 2A,2B,2C,2D,2E,2F). In two patients, the fat rind was so extensive that it simulated intralesional fat on MR imaging in at least one plane. Increased signal in the adjacent muscle on T2-weighted or fluid-sensitive sequences was present in 11 of the patients with myxoma (Figs. 2A,2B,2C,2D,2E,2F and 3A,3B).
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
We speculate that both of these features are the result of the infiltrative pattern of slow growth seen in intramuscular myxoma. Intramuscular myxoma is a paucicellular lesion composed of a mucoid basophilic matrix rich in mucopolysaccharide [4,5,6]. Although lesions may appear well defined on imaging studies, these lesions have no capsule and will infiltrate the adjacent atrophic and edematous striated muscle [2, 4, 6] (Fig. 4A,4B). Mucoid matrix from the lesion may split the cells or become embedded in them [6]. We found that MR imaging planes along the long axis of the involved muscle yielded the greatest information regarding tumor border definition and differentiation of signal in the lesion and the adjacent muscle. The rind of adipose tissue is likely reactive fat, caused by muscle atrophy associated with the slowly growing mass [4] (Fig. 4A,4B). This rind of adipose tissue may be so extensive that it simulates fat in the lesion on MR imaging, as we found in two patients in our study, although it is typically more subtle.
|
|
Although enhancement was variable, intense heterogeneous enhancement was seen in 55% (6/11) of the cases. This pattern of enhancement seemed counterintuitive in that lesions are composed of bland spindle cells with an avascular highly myxoid stroma [6]. The lesion is poorly vascularized, typically with capillarylike vessels [4]. This paucity of vessels can be apparent on arteriography, on which lesions may be identified as defects in the enhanced surrounding muscle [4]. The absence of an elaborate vasculature is in sharp contrast to what is found in myxoid liposarcoma, which tends to show a rich, delicate, plexiform capillary vascular network [7]. Analysis of the enhancement pattern was difficult not only because of the mucoid nature of the lesion but also because of our inability to map the entire myxoma using the histologic samples provided for this retrospective review. Although contrast enhancement has been previously reported [8,9,10], we speculate that the heterogeneous enhancement in most myxomas in our series likely reflects focal areas of relative hypervascularity within the lesions.
Myxomas are usually described as well-defined lesions with a fluidlike signal intensity [8,9,10,11,12,13,14]. Features of perilesional fat rind and increased signal intensity on the adjacent muscle of T2-weighted or fluid-sensitive MR images have been noted but not emphasized as characteristic of intramuscular myxoma [11]. We tested the reliability of these signs as aids to distinguishing intramuscular myxoma from myxoid liposarcoma, the lesion with which it is most frequently confused. In a nonblinded review of 12 patients with myxoid liposarcomas, we found these signs yielded p values of less than 0.002 for the presence of a fat rind and less than 0.008 for the presence of the abnormal muscle signal. The identification of these features alone increases the likelihood a lesion is a myxoma rather than a myxoid liposarcoma by 20.4-fold and 13.4-fold, respectively. Of the six patients with heterogeneously enhancing lesions, three (50%) had both a fat rind and increased signal intensity in the adjacent muscle in the same lesion. It is difficult to know whether a possible variability in the degree of aggressiveness of myxomas was due to the small sample size of our series.
Limitations of our study include the small size of the study sample as well as the limitations inherent to a retrospective study. Although T1-weighted MR images were available for all our patients, the fluid-sensitive MR sequences available for the patients varied and included conventional T2-weighted, T2-weighted fast (turbo) spin-echo, fat-suppressed T2-weighted fast spin-echo, and short tau inversion recovery images. Not all of the studies included images paralleling the long axis of the involved muscle or gadolinium-enhanced images. Finally, no dynamic imaging was done. Although imaging was performed immediately after injection of contrast material, it is possible that enhancement was caused in part by diffusion of the contrast material into the lesion.
MR images that reveal a mass with the signal intensity of fluid, a perilesional fat rind, and an increased signal in the adjacent muscle on the T2-weighted or fluid-sensitive MR sequence are strongly suggestive of intramuscular myxoma. Enhancement of the lesions varies but is most frequently intense and heterogeneous. Although the recognition of these features will likely not obviate biopsy of any individual lesion, it will allow more accurate prebiopsy diagnosis and preoperative planning.
Acknowledgments
We thank Elizabeth J. Atkinson in the Department of Biostatistics, Mayo
Clinic, Rochester, MN, for her assistance in the statistical analysis.
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
This article has been cited by other articles:
|
|
 |
|
  G. Girish, D. A. Jamadar, D. Landry, K. Finlay, J. A. Jacobson, and L. Friedman Sonography of intramuscular myxomas: the bright rim and bright cap signs. J. Ultrasound Med., July 1, 2006; 25(7): 865 - 869. [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]
|
|
|
|
 |
|
 J. Q. Ly, J. L. Bau, and D. P. Beall Forearm Intramuscular Myxoma Am. J. Roentgenol., October 1, 2003; 181(4): 960 - 960. [Full Text] [PDF]
|
|
|
|
 |
|
 M. D. Murphey, G. A. McRae, J. C. Fanburg-Smith, H. T. Temple, A. M. Levine, and A. J. Aboulafia Imaging of Soft-Tissue Myxoma with Emphasis on CT and MR and Comparison of Radiologic and Pathologic Findings Radiology, October 1, 2002; 225(1): 215 - 224. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
