Lumbar Plexus Disorders Presenting as Low Back Pain: A Narrative Review of a Practical Diagnostic Imaging Approach

Low back pain (LBP) is one of the most common causes of medical consultation worldwide and is typically attributed to degenerative spinal disorders. However, a subset of patients presents with LBP related to extra-spinal conditions, including disorders of the lumbar plexus. These conditions are often underrecognized and may mimic lumbar radiculopathy, leading to delayed diagnosis or inappropriate management. The lumbar plexus, formed by the anterior rami of L1-L4 nerve roots, lies deep within the psoas muscle and can be affected by a wide range of pathological processes, including traumatic, compressive, inflammatory, infectious, and neoplastic conditions. A targeted literature search of the PubMed/MEDLINE database was performed to identify relevant English-language articles on lumbar plexus disorders, their imaging features, and diagnostic strategies published from inception to June 2026; representative imaging examples were selected from the co-authors' clinical archives. The review summarizes the relevant anatomy, clinical presentation, and key imaging features of the most common plexus pathologies, including retroperitoneal tumors, psoas hematomas, inflammatory plexopathies, and iatrogenic injuries. Advances in imaging techniques, particularly magnetic resonance imaging (MRI) and magnetic resonance neurography (MRN), have significantly improved the ability to visualize the lumbar plexus and detect pathological changes involving peripheral nerves and surrounding structures. Additionally, a practical diagnostic imaging approach is proposed to assist radiologists and clinicians in recognizing lumbar plexus involvement in patients with atypical low back pain.