Background: Muscle disease is a disorder caused by derangement of the structure or function of muscle fiber, blood supply
and/or connective tissue element of the muscle ,the combination of clinical examination and MRI could improve the accuracy of phenotypic characterization of patients with muscular lesions, This may also be very helpful in the assessment of the degree of muscle compromise not only in the early phases of the disease but also during the follow-up and can be used especially in therapeutic trials. Aim of the work: To assess the role of MRI in detection and evaluation of muscle diseases and its prognostic value for the follow up. Patients and Methods: This study was conducted at the radiology department Ain Shams university, it included thirty patients, they all had clinical diagnosis have of muscular diseases of the lower limb, fulfilled inclusion criteria. Results: The sensitivity of MRI in detection of malignant lesions compared to histo-pathology and clinical diagnosis as gold standered was 83.3%, specificity was 91.7% and accuracy was 90%,76.7% of the studied cases had a benign which was lesion most frequently a hemangioma (10%), also 23.3% of the patients had a malignant lesion which was most frequently metastasis from other tumors (13.3%). Conclusion: MRI is the modality of choice in evaluating lower limb muscular lesions due to its high soft tissue contrast resolution, and multi-planar capabilities. MRI may allow clinicians to more accurately estimate the time required before patient can return to
normal life as well as the risk of recurrent injury.