The role of high resolution 3T MR neurography in the diagnosis of lumbosacral plexopathy and sciatic lesions

Abstract

The ventral rami of L1–L4 and the ventral rami of L4–S3 coalesce to form the lumbar and sacral plexuses, respectively. Together, via the lum¬bosacral trunk, they form the lumbosacral plexus, which innervates the lower extremity . The LS plexus may be affected by a variety of pathologies which can be categorized based on the etiology into systemic ,local and functional causes or based on the anatomy into affection of NMJ ,axon and myelin sheath. The term MR neurography is used to describe the new techniques for nerve imaging that greatly improve the reliability of identification of peripheral nerves in images and often help to identify the exact localization of nerve lesions and spatial lesion patterns which had been the major limitation of clinical and electrophysiological examination . It is mainly T2-based and diffusion-based sequences .Nerve T2 signal , Nerve caliber and the denervation pattern of muscles add crucial are highly sensitive andspecific diagnostic signs for the presenceof neuropathy While Contrast enhancement of peripheral nerves helps in cases of peripheral nerve sheath tumors such as neurofibromas, schwannomas and perineuriomas. With high-resolution 3 tesla (T) magnetic resonance neurography (MRN) techniques, there is significant advancement in the visualization of normal , abnormal lumbosacral (LS) plexus as well as its peripheral nerves. Chhabra et alin 2012 have proposed certain indications for MRN examination which are: 1. Plexus imaging: Nonspecific clinical presentation and suspected lumbosacral plexopathy. 2. Preoperative planning before neurolysis: Evaluate anatomy and confirm nerve morphologic abnormalities in nerve entrapment syndrome. 3. Grading nerve injury: Evaluate and differentiate simple stretch injury from neuroma in continuity and nerve discontinuity. 4. Patient management planning: Characterize and evaluate the extent of the space occupying lesions, such as hematoma, nerve sheath tumor, metastatic disease, pancoast tumor compressing the nerve. 5. Radiation versus recurrent malignancy: Patients presenting with symptoms of plexopathy with history of regional radiation therapy to exclude recurrent malignancy/confirm radiation plexopathy. 6. Known diffuse polyneuropathy with atypical/worsening symptoms: amyloid, lymphoma. 7. Postoperative evaluation: Exclude nerve re-entrapment/persistent impingement in failed surgery cases. 8. Prior to MR guided injection: Perineural (anesthetic/steroid) and scalene/piriformis muscle (Botox) medication injections. 9. Reassure the patients: Chronic pain subjects by demonstrating normal nerves and no lesion.