Magnetic Resonance Neurography of the Lumbar Plexus at the L4-L5 Disc: Development of a Preoperative Surgical Planning Tool for Lateral Lumbar Transpsoas Interbody Fusion (LLIF).

STUDY DESIGN: Observational study. OBJECTIVE: To demonstrate use of magnetic resonance (MR) neurography to visualize the course of the lumbar plexus at the L4-L5 disc space. SUMMARY OF BACKGROUND DATA: Risk of injury to the lumbar plexus during lateral transpsoas approach for lumbar interbody fusion (LLIF) is significant. We describe a new technique for preoperative mapping using magnetic resonance neurography to directly visualize the course of the plexus relative to the L4-L5 disc space. METHODS: Consecutive lumbar plexus MR neurograms (n=35 patients, 70 sides) were studied. Scans were obtained on a Siemens 3-Tesla Skyra magnetic resonance imaging scanner. T1- and T2-color-coded fusion maps were generated along with 3-dimensional models of the lumbosacral plexus with attention to the L4-L5 interspace. The position of the plexus and the shape of the psoas muscle at the L4-L5 interspace were evaluated and recorded. RESULTS: Direct imaging of the lumbar plexus using MR neurography revealed a substantial variability in the position of the lumbar plexus relative to the L4-L5 disc space. The left-side plexus was identified in zone 2 (5.7%), zone 3 (54.3%), and zone 4 (40%) (P = 0.0014); on the right, zone 2 (8.6%), zone 3 (42.9%) or zone 4 (45.7%), and zone 5 (2.9%) (P = 0.01). Right-left symmetry was found in 18 of 35 subjects (51.4%) (P = 0.865). There was no association between the position of the plexus and the shape of the overlying psoas muscle identified. In patients with an elevated psoas (n = 12), the lumbar plexus was identified in zone 3 in 75% and 66% (left and right) compared with patients without psoas elevation (n = 23), 30.4% and 43.5% (left and right). CONCLUSION: The course of the lumbosacral plexus traversing the L4-L5 disc space may be more variable than has been suggested by previous studies. Magnetic resonance neurography may provide a more reliable means of preoperatively identifying the plexus when compared with current methods. LEVEL OF EVIDENCE: 3.

Temporal bone imaging.

Temporal bone imaging is performed for a variety of clinical conditions addressed in the outpatient and acute care setting ranging from hearing loss to trauma. Recent advances in magnetic resonance technology have enhanced the assessment of fine anatomic temporal bone detail and improved the diagnostic sensitivity for important pathology. For example, non-echo planar diffusion weighted imaging increases detection rate and diagnostic confidence of recurrent cholesteatoma. This chapter will focus on relevant temporal bone clinical entities and new MR developments that have come into clinical practice.