MR Imaging of Atraumatic Muscle Disorders

Abstract

Atraumatic disorders of skeletal muscles include congenital variants; inherited myopathies; acquired inflammatory, infectious, or ischemic disorders; neoplastic diseases; and conditions leading to muscle atrophy. These have overlapping appearances at magnetic resonance (MR) imaging and are challenging for the radiologist to differentiate. The authors organize muscle disorders into four MR imaging patterns: (a) abnormal anatomy with normal signal intensity, (b) edema/inflammation, (c) mass, and (d) atrophy, highlighting each of their key clinical and imaging findings. Anatomic muscle variants, while common, do not produce signal intensity alterations and therefore are easily overlooked. Muscle edema is the most common pattern but is nonspecific, with a broad differential diagnosis. Autoimmune, paraneoplastic, and drug-induced myositis tend to be symmetric, whereas infection, radiation-induced injury, and myonecrosis are focal asymmetric processes. Architectural distortion in the setting of muscle edema suggests one of these latter processes. Intramuscular masses include primary neoplasms, metastases, and several benign masslike lesions that simulate malignancy. Some lesions, such as lipomas, low-flow vascular malformations, fibromatoses, and subacute hematomas, are distinctive, but many intramuscular masses ultimately require a biopsy for definitive diagnosis. Atrophy is the irreversible end result of any muscle disease of sufficient severity and is the dominant finding in disorders such as the muscular dystrophies, denervation myopathy, and sarcopenia. This imaging-based classification, in correlation with clinical and laboratory data, will aid the radiologist in interpreting MR imaging findings in patients with atraumatic muscle disorders. RSNA, 2018.

Carpal Tunnel Syndrome Secondary to Ganglion Cyst, with Denervation of Abductor Pollicis Brevis

“…In chronic cases, fatty replacement occurs, resulting in the return of low signal intensity on fluid-sensitive sequences [8]. In CTS, thinning of thenar muscles is a valuable sign indicating chronic denervation atrophy in both MRI and US imaging.…”

Glossary of terms for musculoskeletal radiology

“…Pathogenesis Myonecrosis refers to infarction of skeletal muscle. The most common etiologies include trauma (crush injury), compartment syndrome, prolonged immobilization, poorly controlled diabetes, radiotherapy, sickle cell crisis, or toxin (snake bite) [105]. Myoglobinemia (rhabdomyolysis) is a complication of acute muscle infarction.…”

“…Imaging Radiographs and CT demonstrate muscle mineralization and ossification. On MR, muscle edema, fat infiltration, and atrophy are related to disease activity, severity, and chronicity [105]. By depicting appendicular and axial muscle, whole-body MR can estimate the extent and distribution of myositis as well as treatment response.…”

Radiation-induced Myositis after Proton Beam Therapy to Huge Hepatocellular Carcinoma

“…11 Because radiographic change usually precedes the presentation of symptoms, close observation would be required. When radiologic findings representing muscle edema such as increased T2 signal with bandlike demarcation from nonirradiated tissue in magnetic resonance image after high dose RT is shown, 17 one should consider the possibility of radiation myositis and early intervention may be warranted.…”