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Forearm Intramuscular Myxoma

¹ Department of Radiology, Wilford Hall Medical Center, Ste. 1, 2200 Bergquist Dr., Lackland AFB, TX 78236-5300.
² Penn State University College of Medicine, 500 University Dr., Hershey Medical Center, Hershey, PA 17033.
³ Department of Radiology, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Rd., Bethesda, MD 20814-4799.

Received December 2, 2002; accepted after revision January 13, 2003.

 
Address correspondence to J. Q. Ly.

The opinions and assertions contained herein are the private views of the authors and are not to be construed as official or as representing the views of the Department of the Air Force or the Department of Defense.

A37-year-old man presented with a forearm mass. Physical examination revealed an ill-defined area of swelling at the ventral aspect of the distal forearm that was firm and mildly tender to deep palpation. Findings on forearm radiographs were unrevealing. MRI showed a well-defined and relatively homogeneous cystic intramuscular mass without significant surrounding edema (Fig. 1A); heterogeneous and largely peripheral contrast enhancement was noted (Fig. 1B). The patient elected to have the mass resected. The final histopathologic diagnosis was intramuscular myxoma (Fig. 1C).

View larger version (96K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1A. —37-year-old man with intramuscular myxoma of forearm. Sagittal fat-suppressed T2-weighted image shows oblong benign-appearing uniformly hyperintense intramuscular distal forearm mass along ventral aspect. T1-weighted images (not shown) showed that mass contained lower signal intensity than that of surrounding musculature.

View larger version (106K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1B. —37-year-old man with intramuscular myxoma of forearm. Axial contrast-enhanced fat-suppressed T1-weighted image shows heterogeneously enhancing periphery of mass which involves flexor digitorum superficialis muscle.

View larger version (136K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1C. —37-year-old man with intramuscular myxoma of forearm. Photomicrograph of histopathologic specimen shows hypocellular myxoid substance with pseudocapsule (arrows) between lesion and healthy muscle. (H and E, x10)

Intramuscular myxoma is a benign soft-tissue tumor primarily affecting patients 40–70 years old. Slightly more than half the patients are women. In descending order of occurrence, the mass is most frequently located in the large muscles of the thigh, shoulder, buttocks, or upper arm [1]. The tumor may be surrounded by muscle tissue; attached on one side to muscle fascia; or extend from the periosteum, the subchondral epiphysis, or the joint capsule. Clinically, the tumor most often presents as a firm, painless, palpable, and slowly enlarging soft-tissue mass that is slightly mobile and sometimes fluctuant [2]. However, because the rate of tumor growth also varies, larger tumors with increased growth rates may present with pain, paresthesia, and muscle weakness caused by mass effect. Most intramuscular myxomas are solitary.

Histologically, intramuscular myxomas are composed of a few spindle-shaped cells interspersed within an abundant amount of mucoid substance overlying a loose reticulin framework [2]. It is believed that the tumor originates from modified fibroblasts producing increased amounts of glycosaminoglycans that prevent polymerization of healthy collagen. Gross specimen findings include an ovoid or globular gelatinous mass with scant cystlike areas nested in bundles of skeletal muscle or fascial tissue.

On radiography, an ill-defined soft-tissue density is noticeable [1]. Because of their high mucin and low collagen composition, intramuscular myxomas are sonographically hypoechoic and show low attenuation on CT. T1-weighted images typically show low signal intensity. T2-weighted images show high signal intensity with variable enhancement; most are heterogeneous and hyperintense [1]. Additionally, MRI may show a perilesional fat rind [1, 3]. Bancroft et al. [3] found that the identification of a perilesional fat rind on MRI and of increased signal intensity of the adjacent muscle on T2-weighted images increased the likelihood that a lesion was a myxoma and not a myxoid liposarcoma. Although these radiologic observations may not obviate tumor biopsy, they can aid in distinguishing pre-operatively between benign myxomas and malignant myxoid liposarcomas, two tumors that are often confused radiologically and pathologically [1, 3].

Percutaneous core biopsy provides definitive diagnosis of intramuscular myxoma. These benign tumors are usually treated by local surgical excision. Recurrences are rare and are successfully treated with reexcision.

References

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1. Murphey MD, McRae GA, Fanburg-Smith JC, Temple HT, Levine AM, Aboulafia AJ. Imaging of soft-tissue myxoma with emphasis on CT and MR and comparison of radiologic and pathologic findings. Radiology2002; 225:215 –224[Abstract/Free Full Text]
2. Iwasko N, Steinbach LS, Disler D, et al. Imaging findings in Mazabraud's syndrome: seven new cases. Skeletal Radiol2002; 31:81 –87[Medline]
3. Bancroft LW, Kransdorf MJ, Menke DM, O'Connor MI, Foster WC. Intramuscular myxoma: characteristic MR imaging features. AJR 2002;178:1255 –1259[Abstract/Free Full Text]

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