![]() ![]() The nerve exits from the pelvis below the inguinal ligament in a fibromuscular channel that includes the inguinal ligament, the iliopsoas, and the iliopectineal fascia. In the pelvis, the nerve courses downwards between the iliacus and psoas muscles and immediately lateral to the femoral artery and vein. It is the largest branch of the lumbar plexus. ![]() The femoral nerve originates from the posterior rami of the L2, 元, and L4 nerve roots. The sciatic nerve has both motor and sensory functions: The sciatic nerve then divides in tibial (medial) and common peroneal (lateral) trunks in the distal third of the thigh. In the thigh, it courses between the adductor magnus and the hamstring muscles. The sciatic nerve exits in the pelvis through the greater sciatic foramen, below the inferior margin of the piriformis muscle, and curves around the ischial spine and descends laterally to the common hamstring tendons and posteriorly to the external rotators of the hip as tibial and peroneal divisions (enclosed in a common sheath). The sciatic nerve may descend anteriorly, above, or within the piriformis muscle, with the anterior course being the most common. Later it divides in tibial nerve, comum peroneal nerve, and posterior femoral cutaneous nerve. The sciatic nerve is formed by the ventral rami of the L4 to S3 nerve roots and is the largest peripheral nerve of the body due to its rich perineural fat, being easily assessed in all imaging planes on MRN. (i) Anterior and medial aspects of the mid and distal thigh (iii) Mons pubis and superior labia majora ![]() This article aims to review MRN as a highly precise method to study peripheral nerves, describing anatomy, protocols, applications, pitfalls, and pathologies involved, along with an extensive case presentation and literature review. MRN can directly assess nerve pathologies based on size and signal intensity changes, or indirectly by signs of muscle denervation. Recently, MRN has been performed with higher magnetic field strengths (1.5 or 3.0-T) and high-resolution multiplanar sequences. Although they have high sensitivity, they lack specificity and displaying the anatomic detail needed to localize the nerve lesion and treatment planning. Electromyography (EMG) studies have limitations, mostly related to patient pain, nonspecific results in almost 1/3 of cases, and limited information on location, extent, and etiology of the nerve injury. Historically, evaluation of peripheral neuropathies relied exclusively on neurophysiology and clinical examination to determine the exact location of the pathology. MRN: magnetic resonance neurography MR: magnetic resonance EMG: electromyography. Besides that, common clinical conditions coexist, such as lumbar discogenic pain, hip osteoarthritis, and diabetes. Clinical findings are sometimes confusing with lack of a specific diagnosis of the affected neural segment, or to detect involvement of multiple nerves, as seen in lumbar plexopathy. A wide range of etiologies may be involved in neuropathies: compressions, stretching, penetrating injuries, iatrogenic insults, frictions, entrapments, inflammation, metabolic, toxic, radiation conditions, and tumor diseases. There are several clinical conditions that may require MRI of the lumbosacral plexus ( Table 1). MRN uses superior resolution imaging with the principles of highly weighted fat-suppressed T2 or STIR sequences, large-FOV, three-dimensional sequences, and postcontrast and diffusion-based MR imaging. MRN is an extraordinary and revolutionary technique that meticulously evaluates peripheral nerve diseases, since it allows the visualization of the anatomic origin of the nerves, their trunks course, and their path towards the lower limbs. Recently, technical advances in MRI and particularly with the advent of dedicated high-resolution magnetic resonance neurography (MRN) have optimized such task. In the last two decades, peripheral nerve evaluation was limited from a technical standpoint. Magnetic resonance imaging (MRI) of the peripheral nervous system has been performed since the 1980s and high-resolution neurographic sequences appeared in the 1990s. The lumbosacral plexus represents an intricate network of nerve unifications and divisions that results in terminal nerves responsible for sensory and motor innervation of the pelvis and the lower extremities.
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