Axial diffusion weighted MRI at the level of the cranial border of the sacral ala, demonstrating a possible anterior approach to the lumbosacral plexus in the supine position. A needle (white arrow) can be inserted close to the anterior superior iliac spine and advanced between the psoas major and iliacus muscles. A first injection of local anesthetic into the retropsoas subcompartment will spread to the femoral nerve (red arrow) and the lateral femoral cutaneous nerve (green arrow). A second injection of local anesthetic into the parapsoas compartment will spread to the anterior rami of spinal nerves L4 and L5, the lumbosacral trunk (yellow arrow) and the obturator nerve (pink arrow).