The neural plexuses are intricate networks of nerve fibers interposed between the spinal cord or anterior primary rami proximally and the most proximal portions of peripheral nerves distally. If the lumbar and sacral plexuses are considered as a single entity, then they constitute the largest peripheral nervous system structure. Each of the plexuses varies substantially from the others in its overall vulnerability to injury, the specific types of trauma or disease that most often affects it, and the ease with which it is assessed by the two laboratory diagnostic procedures in current use for doing so: neuroimaging studies and electrodiagnostic examinations.