Magnetic resonance imaging of intramuscular myxoma with histological comparison and a review of the literature.

Objective: To evaluate the magnetic resonance (MR) features of intramuscular myxoma (IM) compared with its pathological findings.

Design: Two radiologists retrospectively reviewed records and imaging studies of patients with histologically proven IM. Two radiologists also analyzed by consensus all the MR studies (pre- and post-contrast T1-weighted and T2-weighted sequences) and a pathologist reviewed the available histological material.

Patients: Seventeen patients with 18 histologically proven IM were reviewed. Histological samples of 11 of these 18 tumors were available for pathological analysis.

Results: There were 14 women and three men, with a mean age of 58.9 years. IM involved predominantly the thigh (n=10). MR imaging showed well-circumscribed intramuscular masses, hypointense on T1-weighted and hyperintense on T2-weighted images. Eleven masses were homogeneous and seven slightly heterogeneous due to fibrous septa. Enhanced MR imaging demonstrated three different patterns: peripheral enhancement (n=1), peripheral and patchy internal enhancement (n=7) or peripheral and linear internal enhancement (n=4). Intratumoral cysts were detected in four masses. MR imaging showed the presence of a pseudocapsule (n=12), fat around the lesion (n=16) and peritumoral edema (n=16). Histologically, all the tumors were hypocellular, hypovascular and myxoid. Peripheral areas of collagenous fibers formed a partial capsule and IM often merged into surrounding muscular fibers. More cellular tumors and those with scanty myxoid stroma tended to show a more prominent internal enhancement.

Conclusion: IM shows several recognizable MR features which suggest its diagnosis.