Magnetic Resonance Neurography of the Lumbar Plexus at the L4–5 Disc: Development of a Preoperative Surgical Planning Tool for Lateral Lumbar Transpsoas Interbody Fusion (LLIF)

Abstract

Introduction The lateral transpsoas approach for lumbar interbody fusion (LLIF) is a minimally invasive surgical technique that is now frequently used to treat common spinal disorders. During LLIF, the course of the plexus within the surgical corridor places it at risk for iatrogenic intraoperative injury. Several previous studies have suggested that the risk of neurological injury during LLIF is higher at L4–L5. Current imaging techniques of assessing the proximity of neural tissue to the L4–L5 disc space have limited capabilities. Magnetic resonance neurography (MRN) is a noninvasive MR imaging tool developed for peripheral nerve imaging. A myriad of clinical applications exist including imaging assessment of lumbosacral plexopathies. In this study, we explored an additional clinical application for this technology as a preoperative planning tool for LLIF. Material and Methods Consecutive lumbar plexus MR neurograms ( n = 27 patients, 54 sides) were studied. All scans were performed on a Siemens 3 T Skyra MRI scanner. The imaging protocol included axial and coronal T1-weighted, axial and coronal T2-weighted spectral adiabatic inversion recovery (SPAIR; Siemens Healthcare), and coronal T2-weighted 3D inversion recovery (3D SPACE; Siemens Healthcare) sequences. Following acquisition, the images were postprocessed using TeraRecon Aquarius iNtuition v4.4 to generate T1- and T2- color-coded fusion maps. 3D models of the lumbosacral plexus with attention to the L4–L5 interspace were generated using the GE AW Suite v2 (General Electric). The L4–L5 intervertebral space was divided into six zones according to Moro method. Zones I to IV were distributed equidistantly between the anterior and posterior margins. The position of the plexus and the shape of the psoas muscle at the L4–L5 interspace was evaluated and recorded. Results Direct imaging of the lumbar plexus using MR neurography revealed variability in the position of the plexus relative to the L4–L5 interbody space. In this series of 27 patients, there was significant variability in the anatomic position of the lumbar plexus from patient-to-patient and right-to-left in individual patients. The left-side lumbar plexus was identified in zones III (55%) and zone IV (44%) ( p = 0.56). On the right side the plexus was most frequently identified in zones III (44%) or zone IV (44%) however was also identified in zone II (7.4%) or posterior (3.7%) ( p = 0.009). Right–left symmetry of the plexus relative to the disc space was found in 44% of the subjects. There was no correlation between the position of the plexus and the shape the overlying psoas muscle identified. Conclusion MRN is a noninvasive imaging technique for visualizing the lumbosacral plexus. The course of the lumbosacral plexus traversing the L4–5 disc space may be more variable than has been suggested by previous studies. MRN may provide a more reliable means of preoperatively identifying the plexus when compared with current methods. The ability to assess the location of the plexus may aid in preoperative planning and reduce neurological complications.