Magnetic resonance imaging of pyomyositis in 43 cases

Purpose: To describe the magnetic resonance imaging (MRI) findings in pyomy ositis. Methods and materials: Forty-three patients with proven muscle infe ction (30 males, 13 females) ranging in age from 14 to 86 years (mean 42 ye ars) were studied with MRI. The initial clinical diagnose were soft tissue infection (n = 27), neoplasm (n = 12), thrombophlebitis (n = 3), and lymphe dema (n = 1). Spin-echo T1- and T2-weighted images were obtained in all cas es and STIR sequence in 6. Spin-echo T1-weighted images after Gd-DTPA injec tion were obtained in 16 cases. The signal intensity findings, the extent o f the abnormalities in the soft tissue (muscle, fascial and subcutaneous in volvement), the presence of fluid collections, and the involvement of neigh bouring bone and joint were reviewed retrospectively. Results: A hyperinten se signal on T2-weighted and STIR images were detected in all patients. Flu id collections were seen in 21 cases as localized areas of hypointensity on the T1-weighted images, and highly hyperintense areas on the T2-weighted i mages. In four patients a rim of high signal intensity was seen around the fluid collection on the T1-weighted images. On contrast-enhanced T1-weighte d images there was diffuse enhancement in the patients without fluid collec tions that was heterogeneous in seven and homogeneous in two. After Gd-DTPA all fluid collections showed a central area without enhancement and a well -defined enhancing peripheral rim. Involvement of adjacent structures inclu ded subcutaneous tissue (n = 25), bone marrow (n = 14), fascial planes (n = 15) and joints (n = 11). Conclusion: MRI is useful in the assessment of py omyositis and in determining the location and extension. A hyperintense rim on unenhanced T1-weighted images and peripheral enhancement after Gd-DTPA are useful for identifying the number, size, and location of soft-tissue ab scesses. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.