A new anatomical brachial plexus variation during interscalene block.

We aimed to present our anesthetic management for an ultrasound-guided (USG) interscalene block in the presence of a new brachial plexus variation in a 59-year-old male patient underwent shoulder arthroscopy. An accessory muscle between the anterior scalene (ASM) and middle scalene muscle (MSM) was viewed via ultrasound. When four roots that the accessory muscle separated into two groups, which should be normally present between the ASM and MSM were displayed, we decided to use nerve stimulator to perform block. The contraction response from the deltoid muscle group from both root groups was regarded as a possible new brachial plexus variation in the C5 nerve root. For interscalene block, 30 ml of 0.375% bupivacaine was used via multi-injection. We confirmed this new brachial plexus variation with magnetic resonance neurography for the first time in a patient. Interscalene block should be definitely performed under USG and when a new anatomical variation is suspected, roots should be separated with a nerve stimulator to increase the success of the block.