Ultrasound localization of the sacral plexus using a parasacral approach.

In this report, we describe the feasibility of locating the sacral plexus nerve using a parasacral approach and an ultrasound-guided technique. The parasacral region using a curved probe (2-5 MHz) was scanned in 17 patients in search of the medial border of the ischial bone and the lateral border of the sacrum, which represent the limit of the greater sciatic foramen. In addition, attempts were made to identify the piriformis muscles and the gluteal arteries. The sacral plexus was identified at the level of the sciatic foramen as a round hyperechoic structure. The gluteal arteries were identified in 10 of 17 patients, but we failed to positively identify the piriformis muscle in any patient. To confirm localization of the sacral plexus, an insulated needle attached to a nerve stimulator was advanced and, in each case, a sacral plexus motor response was elicited (plantar flexion-12, dorsal flexion-1, hamstring muscle stimulation-3, gastrocnemius muscle stimulation-1-not recorded) at a current between 0.2 and 0.5 mA. No complications were observed. This report confirms the feasibility of using ultrasound to locate the sacral plexus using a parasacral approach.