Clinical Implications of Anatomical Variations in Nerves and Adjacent Structures for Regional Anesthesia: A Narrative Review.

Anatomical variations in nerves are common and can significantly impact ultrasound-guided regional anesthesia. They directly influence needle trajectory, local anesthetic spread, and block efficacy, contributing to procedural failure or complications. However, the literature specifically addressing the clinical implications of neural variations for regional anesthesia remains limited. This narrative review synthesizes evidence on three key aspects: (1) variations of common peripheral nerves and their clinical significance in regional anesthesia (including the terminal branches of the trigeminal nerve, suprascapular nerve, phrenic nerve, lumbar plexus, saphenous nerve, obturator nerve, and sciatic nerve); (2) variations of major vessels relevant to regional anesthesia and their clinical significance in regional anesthesia (including the Adamkiewicz artery and vertebral artery); (3) variations of the spine and spinal nerve roots and their clinical significance in regional anesthesia. This review systematically synthesizes current evidence on these anatomical variations and introduces practical resources, including regional ultrasound guidance and tables correlating specific variants with technical modifications, to enhance ultrasound recognition and clinical decision-making, thereby serving as a valuable reference for clinicians.