Acute myonecrosis on MRI: etiologies in an oncological cohort and assessment of interobserver variability.

Abstract

To determine the etiologies of myonecrosis in oncology patients and to assess interobserver variability in interpreting its MRI features. Pathology records in our tertiary cancer hospital were searched for proven myonecrosis, and MRIs of affected regions in those patients were identified. MRI reports that suggested myonecrosis were also identified. Each MRI was reviewed independently by 2 out of 6 readers to assess anatomical site, size, and signal intensities of muscle changes, and the presence of the previously reported stipple sign (enhancing foci within a region defined by rim enhancement). The stipple sign was assessed again, weeks after a training session. Cohen kappa and percentage agreement were calculated. Medical records were reviewed for contemporaneous causes of myonecrosis. MRI reports in 73 patients suggested the diagnosis of myonecrosis; pathological proof was available in another 2. Myonecrosis was frequently associated with radiotherapy (n = 34 patients, 45%); less frequent causes included intraoperative immobilization, trauma, therapeutic embolization, ablation therapy, exercise, and diabetes. Myonecrosis usually involved the lower extremity, the pelvis, and the upper extremity; mean size was 13.0cm. The stipple sign was observed in 55-100 % of patients at first assessment (κ = 0.09-0.42; 60-80% agreement) and 55-100 % at second (κ = 0.0-0.58; 72-90% agreement). Enhancement surrounded myonecrosis in 55-100% patients (κ = 0.03-0.32; 58-70% agreement). Myonecrosis in oncology patients usually occurred after radiotherapy, and less commonly after intraoperative immobilization, trauma, therapeutic embolization, ablation therapy, exercise, or diabetes. Although interobserver variability for MRI features of myonecrosis exists (even after focused training), a combination of findings facilitates diagnosis and conservative management.