Muscle fat infiltration: a narrative review of the magnetic resonance (MR)-based evaluation methods and their clinical applications.

Background and Objective: Muscle fat infiltration (MFI) can be seen in several pathologies of various origin including neuromuscular, endocrinological, or musculoskeletal etiologies. Its evaluation is possible through medical imaging, especially MRI, using qualitative or quantitative methods. This paper is an overview of the techniques used to evaluate MFI in different pathologies. Methods: The literature search was performed on the PubMed database for articles published in English between 2010 and end of January 2023. The keywords used were: (Fat infiltration of the muscle) AND magnetic resonance imaging (MRI). In total, 159 articles were included. Key Content and Findings: Qualitative methods of MFI evaluation represented 20% of the studies, with the Goutallier classification being the most used, especially in the setting of rotator cuff tears. Quantitative methods were used in most studies (80%), with the Dixon technique being the most adopted. The evaluation of MFI was used for the assessment of endocrinological, neuromuscular and musculoskeletal disorders. Spinal pathologies, including low back pain and spinal deformities, were the most represented (44% of the studies). Conclusions: This review shows the importance of automated MFI calculation using MRI to monitor the progression of diseases, assess the effect of treatments, or predict post-surgical complications such as in the setting of adult spinal deformity. This review also showed the importance of automation of MFI assessment, particularly using the Dixon technique, to make its use easier in clinical settings and open MFI assessment applications to other diseases.