A Didactic Ultrasound Manual for identifying lumbar Plexus Peripheral Nerves in the lower limb: Lower Abdominal Wall,...

The lumbar plexus, formed by the anterior rami of T12/L1 to L4/L5, provides the main neural supply to the lower abdominal wall, groin, and anterior-medial thigh. Its principal peripheral branches (the iliohypogastric, ilioinguinal, genitofemoral, lateral femoral cutaneous, femoral, and obturator nerves) are clinically relevant targets for invasive diagnostic and therapeutic procedures, including nerve blocks and neuromodulatory techniques. This manual aims to describe how to visualize these six main lumbar plexus branches using ultrasound guidance.

For each nerve, this guide summarizes its typical anatomical course, key clinical considerations related to neuropathy or iatrogenic injury, the most relevant anatomical landmarks, recommended transducer positioning, and characteristic sonographic appearance. The text is complemented by illustrations of probe placement, schematic depictions of nerve pathways, and representative ultrasound images.

This manual provides a structured ultrasound-based approach for identifying the main lumbar plexus branches in the lower abdominal wall, groin, and thigh. It details the anatomical and sonographic features that facilitate nerve recognition and supports precise probe positioning and needle guidance when these nerves are targeted in clinical practice.

Ultrasound guidance is encouraged when performing procedures involving lumbar plexus branches, as it may improve procedural accuracy and patient safety by enabling precise needle placement while reducing the risk of injury to adjacent non-target structures. This manual offers a practical anatomical and sonographic reference for clinicians performing ultrasound-guided interventions in this region.