Introduction

Traumatic and entrapment injuries to the brachial plexus vary in severity and occur when the brachial plexus is stretched, compressed, or avulsed. These injuries affect a range of age groups, from neonates with neonatal brachial plexus palsy to adults with traumatic injuries and entrapment conditions often resulting in pain, numbness, and weakness. Recovery is challenging due to multiple factors such as the intricate physiology of nerve regeneration, or the presence of pre-surgical delay [1], [2]. A primary reason for delayed surgical intervention is the difficulty in diagnosing this injury [1], [2], [3]. Additionally, both traumatic brachial plexus injuries and entrapment of brachial plexus are relatively rare, potentially limiting clinician experience [3], [4]. In the current literature, Magnetic resonance imaging (MRI) is the most widely accepted imaging tool for the diagnosis of traumatic and entrapment related brachial plexus injuries [5], [6], [7]. Some studies have shown it has superior diagnostic capabilities compared to nerve and muscle electrophysiology studies as well as ultrasound [8], [9], [10], [11]. MRI is useful not only for diagnosing brachial plexopathies but also aids in surgical planning. Accurate identification of the location and extent of brachial plexus injury is important for selecting the appropriate treatment and planning surgical reconstruction.

MRI requires careful selection of sequences to accurately visualize brachial plexus pathology, with fat suppression techniques playing a key role [12]. These techniques improve contrast by reducing fat signals, making nerves and injuries clearer for diagnosis. Chemical Shift Selective Fat Saturation (CHESS/Fat-Sat) and Short Tau Inversion Recovery (STIR) were the first fat suppression techniques described for imaging nerves, improving nerve-to-background contrast [12]. However, newer techniques offering potential technical advantages are constantly being developed, such as the Dixon technique which offers effective fat-water separation capabilities, increased robustness to field inhomogeneities/susceptibility artifacts, and increased flexibility for different contrasts [13], [14]. The reported use in the literature of these newer, advanced fat suppression techniques remains unexplored.

Within the broader scope of MRI, specialized imaging modalities have been developed to further enhance nerve visualization. Magnetic Resonance Neurography (MRN) is a valuable non-invasive tool for assessing peripheral nerves, particularly for entrapments and injuries. It employs high-resolution T2-weighted sequences against a fat-suppressed background. A prime example is the 3D turbo spin echo with Sampling Perfection with Application optimized Contrast using different flip angle Evolution (SPACE) STIR sequence, which optimizes fat suppression and enables multi-plane imaging [12]. In heavily T2-weighted 3D MR neurography, intravenous gadolinium may improve vascular suppression through T2 shortening, thereby increasing nerve conspicuity; however, its use is sequence- and indication-dependent [15], [16]. Although advanced fat suppression techniques show promise for diagnosing brachial plexus injuries, studies on their reported use in the literature also remain limited, much like the Dixon technique. A broader lack of comprehensive research exists regarding the most commonly used fat suppression methods and the clinical adoption of emerging techniques. Familiarity with the adoption patterns, strengths, weaknesses of these methods can help guide protocol design, promote standardization, and by extension - improve diagnostic accuracy. Identifying utilization trends may also provide insight into the integration of newer techniques into clinical practice [17].

This scoping review aims to examine the existing literature to assess which MRI fat suppression and advanced techniques are used in diagnosing traumatic and entrapment-related brachial plexus injuries (TEBPI) in both adult and pediatric populations and to explore the reported use in the literature of emerging fat suppression techniques.